Rising sea levels could lead to more methane emitted from wetlands

As sea levels rise due to global warming, ecosystems are being altered. One small silver lining, scientists believed, was that the tidal wetlands found in estuaries might produce less methane -- a potent greenhouse gas -- as the increasing influx of seawater makes these habitats less hospitable to methane-producing microbes.

However, research from biologists at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley indicates that these assumptions aren't always true. After examining the microbial, chemical, and geological features of 11 wetland zones, the team found that a wetland region exposed to a slight amount of seawater was emitting surprisingly high levels of methane -- far more than any of the freshwater sites.

Their results, now published in mSystems, indicate that the factors governing how much greenhouse gas is stored or emitted in natural landscapes are more complex and difficult to predict than we thought.

"We looked at how many methanogens, the organisms that make methane, are present in soils at these sites and it wasn't really well correlated with the amount of methane observed," said senior author Susannah Tringe, director of Berkeley Lab's Environmental Genomics & Systems Biology Division. "And even if you look at the amount of methanotrophs, organisms that eat methane, in combination with methanogens, that doesn't seem to fully explain it."

Tringe and her colleagues took soil samples from the 11 sites and used high-throughput sequencing to analyze DNA from organisms found in the samples, including bacteria, viruses, and fungi. They examined what genes were present in the sequences and mapped them to known functions -- for example, identifying genes known to be involved in metabolizing nitrogen or genes from bacteria that use sulfate during respiration. Then they worked to model how the genetic information they found, combined with chemical factors in the soil and water, could result in the methane emissions they observed.

Across most of the sites, which ranged from freshwater to full seawater salinities, the amount of methane emitted was inversely related to the amount of salt water that was flowing in and mingling with the river water. But at one site, which had been restored in 2010 from a seasonal grassy pasture for livestock grazing back to its original wetland habitat, the team saw high methane emissions despite the moderate amount of salt water.

Seawater contains more sulfate (an ion with sulfur and oxygen) than freshwater, leading to the assumption that increased influx of seawater in these environments would lead to less methane production as the methanogens that use CO2 to make cellular energy are outcompeted by the bacteria that use sulfate instead.

"Ultimately, we found that there were significant influences from other bacterial groups like the ones that break down carbon and even organisms that are better known as nitrogen cyclers, and we couldn't readily explain the methane emissions by something as simple as, for example, how much sulfate is available or how many methanogens are there," said Tringe.

Another concept in ecology is that restoring habitats to their native state can boost carbon storage, improve water quality, and increase wildlife populations. In recent decades, wetlands have been increasingly recognized as critical ecosystems for these environmental services, leading to widespread efforts to restore ecosystems by removing barriers, pollution, and non-native organisms.

Modeling work by co-author Dennis D. Baldocchi, Executive Associate Dean and professor of Biometeorology at UC Berkeley, suggests that although the restored wetland is adding greenhouse gas to the atmosphere currently, the ecosystem will stabilize and begin to serve as a net carbon sink within 100 to 150 years. This may not be the timeline that stakeholders were hoping for when they restored the area with the goal of carbon sequestration.

"We want to know if these systems will act as long-term carbon sinks," said Baldocchi. "And these microbiological investigations can help refine our models and predictions."

Tringe noted that other labs have observed increased methane production from wetland soils with increased salinity. Scientists from Duke University took soil core samples from a coastal freshwater wetland and exposed them to artificial seawater, and artificial seawater lacking sulfate. In both cases, methane production went up. Tringe's lab recently collaborated with Marcelo Ardón of North Carolina State University to analyze the microbial communities in those soils.

"There was this expectation that sulfate would be the most important thing. And in those studies, not only did salt water stimulate methane production, which again is kind of counter to the dogma that sulfate is important, it happened whether you had sulfate there or not; in fact the sulfate didn't have a big effect on the methane emissions," said Tringe. "So I think these experimental manipulations are reconfirming the story that there's more nuanced effects of seawater intrusion than just a sulfate addition, and also more nuanced factors behind ecosystem restoration."

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Stability inspection for West Antarctica shows: marine ice sheet is not destabilized yet, but possibly on a path to tipping

Antarctica's vast ice masses seem far away, yet they store enough water to raise global sea levels by several meters. A team of experts from European research institutes has now provided the first systematic stability inspection of the ice sheet's current state. Their diagnosis: While they found no indication of irreversible, self-reinforcing retreat of the ice sheet in West Antarctica yet, global warming to date could already be enough to trigger the slow but certain loss of ice over the next hundreds to thousands of years.

"With more and more ice being lost in Antarctica over the last years, concerns have been raised whether a tipping point has already been crossed and an irreversible, long-term collapse of the West Antarctic Ice Sheet has already been initiated," explains Ronja Reese from the Potsdam Institute for Climate Impact Research (PIK) and the Northumbria University, Newcastle. "The results of our studies deliver two messages: First, while a number of glaciers in Antarctica are retreating at the moment, we find no indication of irreversible, self-reinforcing retreat yet, which is reassuring. However, our calculations also clearly indicate that an onset of an irreversible retreat of the ice sheet in West Antarctica is possible if the current state of the climate is sustained."

The main driver of ice loss in West Antarctica is relatively warm ocean water that amplifies melting underneath the ice shelves, which are the floating extensions of the grounded ice sheet. Melting of these ice shelves can enhance ice loss as it speeds up the grounded sections of the ice sheet. That is why the Antarctic margin with its grounding lines -- the zone where the grounded and the floating ice are connected -- is a key indicator of ice sheet health. An accelerated retreat of the grounding lines could indicate a forthcoming collapse of large marine regions of West Antarctica's ice sheet -- those parts of the ice sheet that are grounded below sea level.

Evolving over 10,000 years, triggered today: irreversible ice-loss and sea-level rise

Using state-of-the-art ice sheet models, the researchers not only conducted a thorough inspection of signs of irreversible retreat of marine sectors of the Antarctic ice sheet at present, they also ran simulations to investigate how the ice sheet would evolve over the next 10,000 years if current conditions remained unchanged. These hypothetical experiments indicate that even with no additional warming beyond what we have already experienced today, an irreversible collapse of some marine regions of West Antarctica's ice sheet is possible. Because the ice reacts to changes in temperature very slowly, the authors find that collapse occurs in their simulations at the earliest in 300 to 500 years from now, under current climate forcing. A full collapse would take centuries to millennia.

"The thing with sea-level rise from Antarctica is not that changes would happen overnight as an immediate threat to coastal communities. The process of melting would happen over hundreds or thousands of years. However, the cause could be human actions today, as they have the power to trigger and commit a future of 10,000 years to several meters of global sea-level rise. And stronger warming in the future would even speed up this process," Julius Garbe from PIK stresses.

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Scientists discover 36-million-year geological cycle that drives biodiversity

Movement in the Earth's tectonic plates indirectly triggers bursts of biodiversity in 36-million-year cycles by forcing sea levels to rise and fall, new research has shown.

Researchers including geoscientists at the University of Sydney believe these geologically driven cycles of sea level changes have a significant impact on the diversity of marine species, going back at least 250 million years.

As water levels rise and fall, different habitats on the continental shelves and in shallow seas expand and contract, providing opportunities for organisms to thrive or die. By studying the fossil record, the scientists have shown that these shifts trigger bursts of new life to emerge.

The research has been published in the journal Proceedings of the National Academy of Sciences, led by Associate Professor Slah Boulila from Sorbonne University in Paris.

Study co-author Professor Dietmar Müller, from the School of Geosciences at the University of Sydney, said: "In terms of tectonics, the 36-million-year cycle marks alterations between faster and slower seafloor spreading, leading to cyclical depth changes in ocean basins and in the tectonic transfer of water into the deep Earth.

"These in turn have led to fluctuations in the flooding and drying up of continents, with periods of extensive shallow seas fostering biodiversity.

"This work was enabled by the GPlates plate tectonic software, developed by the EarthByte Group at the University of Sydney, supported by Australia's National Collaborative Research Infrastructure Strategy (NCRIS) via AuScope."

The team based their findings on the discovery of strikingly similar cycles in sea-level variations, Earth's interior mechanisms and marine fossil records.

Scientists now have overwhelming evidence that tectonic cycles and global sea level change driven by Earth's dynamics have played a crucial role in shaping the biodiversity of marine life over millions of years.

"This research challenges previous ideas about why species have changed over long periods," Professor Müller said.

"The cycles are 36 million years long because of regular patterns in how tectonic plates are recycled into the convecting mantle, the mobile part of the deep Earth, similar to hot, thick soup in a pot, that moves slowly."

Professor Müller said the Cretaceous Winton Formation in Queensland serves as a prime example of how sea-level changes have shaped ecosystems and influenced biodiversity in Australia.

The formation, renowned for its collection of dinosaur fossils and precious opal, provides a valuable window into a time when much of the Australian continent was flooded.

As sea levels rose and fell, the flooding of the continent created expanding and contracting ecological recesses in shallow seas, providing unique habitats for a wide range of species.

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Prehistoric human migration in Southeast Asia driven by sea-level rise

An interdisciplinary team of scientists at Nanyang Technological University, Singapore (NTU, Singapore) has found that rapid sea-level rise drove early settlers in Southeast Asia to migrate during the prehistoric period, increasing the genetic diversity of the region today.

The Malay Peninsula and the islands of Sumatra, Borneo, and Java were originally part of a large landmass of rainforests and coastal mangroves in the South Asia continental shelf known as 'The Sundaland' some 26,000 years ago.

But during the last major period of global warming in Earth's history, from the Last Glacial Maximum period (approximately 26,000 -- 20,000 years ago) to the mid-50 Holocene (approximately 6,000 years ago), sea level rose 130 metres. The rise in sea level flooded and submerged half of The Sundaland, breaking land bridges and splitting the large landmass into smaller islands of the region today.

To understand the impact on humans living in The Sundaland during one of the most dramatic sea-level rises in the Earth's history, the team of NTU Singapore scientists reconstructed the history of the landmass using two different approaches: paleogeography -- the study of historical physical landscapes, and population genetics.

Lead investigator, Assistant ProfessorKim Hie Lim from NTU's Asian School of the Environment (ASE), and the Singapore Centre for Environmental Life Sciences Engineering (SCELSE) at NTU said, "Environmental changes have profound impacts on human history, driving population migration, growth, and distribution. However, less discussed is how environmental changes can shape the genetics of populations. Our work is the first reported instance to provide proof that sea-level rise changed the genetic makeup of human populations in Southeast Asia -- a legacy that continues to impact current populations."

Using data for Southeast and South Asia's sea-level history, including ancient Singapore records established by the NTU's Earth Observatory of Singapore (EOS) and ASE, the research team constructed paleogeographic maps dating from 26,000 years ago to the present.

The NTU team also used whole-genome sequence data from 59 ethnic groups, including that belonging to populations native to Southeast and South Asia from 50,000 years ago. By analysing the high-quality genome data, the team was able to infer the genetic ancestry and demographic history of the groups, including their population size and distribution.

While researchers elsewhere have studied population history based on genetics, most of them used mitochondrial DNA (genes inherited from the mother), which does not tell the full picture of individual ancestry.

By using whole-genome sequence data -- precise information of an individual's entire genetic makeup inherited from both the mother and the father -- the NTU study offers an unbiased demographic history of the indigenous populations inhabiting The Sundaland.

The whole-genome sequence data was generated by the non-profit organisation GenomeAsia 100K. Launched in 2016 and hosted by NTU, the initiative aims to better understand the genome diversity of Asian ethnicities by sequencing 100,000 genomes of people living in Asia.

Contributing author, Professor Stephan Schuster, President's Chair in Genomics at NTU's School of Biological Sciences, Research Director of SCELSE, and Scientific Chair of GenomeAsia 100K, said, "GenomeAsia 100K systematically generates maps of Asian human genetic diversity, including indigenous ethnicities who have occupied the region for a long time. Integrating those maps with paleoclimatic data allows us now to understand exactly how past climatic events have resulted in ancient human migrations, as well as their impact on today's population structure."

The research is aligned with the NTU 2025 strategy, where the University adopts more collaborative, global and interdisciplinary means of research to address Singapore's national research priorities, such as health & society.

Piecing together the story of human migration in ancient Sundaland

Combining findings from the two approaches, the scientists inferred the changes in population density from the high quality historical paleogeographic maps generated.

The map paints a picture of prehistoric human migration in The Sundaland, showing that the earliest documented instance of forced human migration was driven by sea level rise.

The scientists found that two periods of rapid sea level rise (rates of sea level rise at46 mm/year and 22 mm/year)promoted the separation of populations into smaller groups across The Sundaland, as the large landmass became split into smaller islands, forcing people to disperse.

Even as the landmass decreased after the rapid sea level rises, temperature increased from the Last Glacial Maximum, creating a favourable living environment to support human population growth. This caused population density to surge by at least eight times from the Last Glacial Maximum, especially in the Island Southeast Asian region, including Malay Peninsula, Sumatra, and Borneo.

As a result, overpopulation drove people to migrate in search of new places to settle and the people in The Sundaland later migrated back northwards, towards Mainland Southeast Asia and South Asia.

This finding is supported by evidence of migration by the ancestors of the Malaysian indigenous group (Malaysia Negrito, or commonly referred to as 'Orang Asli') into South Asian tribal groups (Austroasiatic speakers). Genetic analysis confirmed common genetic ancestry between the Malaysian and South Asian indigenous groups.

The entire process of migration therefore shaped the diverse ethnicities across Southeast and South Asian regions, as early settlers of The Sundaland interbred across different indigenous groups.

Co-author of the study, Dr Li Tanghua, Senior Research Fellow at NTU's EOS said, "Based on our findings, the Orang Asli Malaysian indigenous group can be considered the first 'casualties' of sea-level rise, or what are known as 'climate refugees' today. The population had no choice but to move from their original territory due to environmental pressures. This forced migration caused an indelible change to the genetic footprint of South Asians, contributing to one of the most ethnically diverse regions in the world."

Findings useful to understand impact of sea level rise on human ancestry

The study, published in the peer-reviewed journal Communications Biology in February, is the first to trace the impact of prehistoric sea level rise to human ancestry in Southeast Asia.

Co-author of the study, Professor Benjamin Horton, Director of NTU's EOS, said, "The study of past sea levels is essential to predicting how increasing amounts of atmospheric carbon dioxide will alter Earth's climate and raise future sea levels. These projections inform how societies can mitigate and adapt to climate change impacts."

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What crocodile DNA reveals about the Ice Age

What drives crocodile evolution? Is climate a major factor or changes in sea levels? Determined to find answers to these questions, researchers from McGill University discovered that while changing temperatures and rainfall had little impact on the crocodiles' gene flow over the past three million years, changes to sea levels during the Ice Age had a different effect.

"The American crocodile tolerates huge variations in temperature and rainfall. But about 20,000 years ago - when much of the world's water was frozen, forming the vast ice sheets of the last glacial maximum - sea levels dropped by more than 100 metres. This created a geographical barrier that separated the gene flow of crocodiles in Panama," says postdoctoral fellow José Avila-Cervantes, working under the supervision of McGill professor Hans Larsson.

The researchers point out that the crocodiles are good swimmers, but they can't travel long distances on land. As a result, the Caribbean and Pacific crocodile populations were isolated from each other, and consequently have undergone different genetic mutations.

The team compared the climate tolerance of living populations of American crocodiles (Crocodylus acutus) to the paleoclimate estimates for the region over the past 3 million years - the time span of extreme climate variation during the Ice Age.

"This is one of the first times Ice Age effects have been found in a tropical species. It's exciting to discover effects of the last Ice Age glaciation still resonate in the genomes of Pacific and Caribbean American crocodiles today," says Larsson, Professor of Biology at the Redpath Museum of McGill University.

"Discovering that these animals would have easily tolerated the climate swings of the Ice Age speaks to their resilience over geological time. Only humans in recent decades of hunting and land development seem to really affect crocodiles," he says. The findings offer new insight into how environmental drivers affect genetic evolution and where conservation efforts of particular crocodile populations in Panama should be focused.

From Science Daily

Bering Land Bridge formed surprisingly late during last ice age

A new study that reconstructs the history of sea level at the Bering Strait shows that the Bering Land Bridge connecting Asia to North America did not emerge until around 35,700 years ago, less than 10,000 years before the height of the last ice age (known as the Last Glacial Maximum).

The new findings, published the week of December 26 in Proceedings of the National Academy of Sciences, indicate that the growth of the ice sheets -- and the resulting drop in sea level -- occurred surprisingly quickly and much later in the glacial cycle than previous studies had suggested.

"It means that more than 50 percent of the global ice volume at the Last Glacial Maximum grew after 46,000 years ago," said Tamara Pico, assistant professor of Earth and planetary sciences at UC Santa Cruz and a corresponding author of the paper. "This is important for understanding the feedbacks between climate and ice sheets, because it implies that there was a substantial delay in the development of ice sheets after global temperatures dropped."

Global sea levels drop during ice ages as more and more of Earth's water gets locked up in massive ice sheets, but the timing of these processes has been hard to pin down. During the Last Glacial Maximum, which lasted from about 26,500 to 19,000 years ago, ice sheets covered large areas of North America. Dramatically lower sea levels uncovered a vast land area known as Beringia that extended from Siberia to Alaska and supported herds of horses, mammoths, and other Pleistocene fauna. As the ice sheets melted, the Bering Strait became flooded again around 13,000 to 11,000 years ago.

The new findings are interesting in relation to human migration because they shorten the time between the opening of the land bridge and the arrival of humans in the Americas. The timing of human migration into North America remains unresolved, but some studies suggest people may have lived in Beringia throughout the height of the ice age.

"People may have started going across as soon as the land bridge formed," Pico said.

The new study used an analysis of nitrogen isotopes in seafloor sediments to determine when the Bering Strait was flooded during the past 46,000 years, allowing Pacific Ocean water to flow into the Arctic Ocean. First author Jesse Farmer at Princeton University led the isotope analysis, measuring nitrogen isotope ratios in the remains of marine plankton preserved in sediment cores collected from the seafloor at three locations in the western Arctic Ocean. Because of differences in the nitrogen composition of Pacific and Arctic waters, Farmer was able to identify a nitrogen isotope signature indicating when Pacific water flowed into the Arctic.

Pico, whose expertise is in sea level modeling, then compared Farmer's results with sea level models based on different scenarios for the growth of the ice sheets.

"The exciting thing to me is that this provides a completely independent constraint on global sea level during this time period," Pico said. "Some of the ice sheet histories that have been proposed differ by quite a lot, and we were able to look at what the predicted sea level would be at the Bering Strait and see which ones are consistent with the nitrogen data."

The results support recent studies indicating that global sea levels were much higher prior to the Last Glacial Maximum than previous estimates had suggested, she said. Average global sea level during the Last Glacial Maximum was about 130 meters (425 feet) lower than today. The actual sea level at a particular site such as the Bering Strait, however, depends on factors such as the deformation of the Earth's crust by the weight of the ice sheets.

"It's like punching down on bread dough -- the crust sinks under the ice and rises up around the edges," Pico said. "Also, the ice sheets are so massive they have gravitational effects on the water. I model those processes to see how sea level would vary around the world and, in this case, to look at the Bering Strait."

The findings imply a complicated relationship between climate and global ice volume and suggest new avenues for investigating the mechanisms underlying glacial cycles.

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Scientists chart 45 million years of Antarctic temperature change

Molecular fossils and machine learning have enabled scientists to build the first charts of Antarctic ocean temperatures over the past 45 million years, offering important insights into future sea level changes.

The team, led by scientists from Victoria University of Wellington (NZ) and Birmingham (UK) say their results suggest we are nearing a 'tipping point' where ocean warming caused by atmospheric CO2 will cause catastrophic rises in sea levels because of melting ice sheets. Their results are published today (15 September 2022) in Nature Geoscience.

In the study, the team examined molecular fossils from core samples taken during ocean drilling projects. The fossil remains are in fact single lipid (insoluble in water) molecules produced by archaea -- single-celled organisms which are similar to bacteria. The archaea adjust the composition of their outer membrane lipids in response to changing sea temperatures. By studying these changes, scientists can draw conclusions about the ancient sea temperature which would have surrounded a particular sample as it died.

While these molecular fossil techniques are well used by palaeoclimatologists, the team from Wellington (NZ) and Birmingham (UK) went a step further. They used machine learning to refine the technique, giving the first record to date of changing Antarctic sea temperatures throughout much of the Cenozoic period -- covering the past 45 million years.

That means scientists are able to pinpoint much more accurately the historic temperatures which caused ice sheets to grow and shrink during that period. The future loss of ice sheets and the retreat of glaciers in the Antarctic is critically important as melting ice in the region could sea levels to rise by up to 50 m.

"The record we've produced offers a much more robust overview of fluctuating Antarctic temperatures and how these relate to changes in the amount of ice, and the topography of Antarctica, over this period and paves the way for improved estimates of future events," explains the Birmingham lead author Dr James Bendle.

The link between CO2, sea-surface temperatures and the amount of ice on Antarctica is clear through the last 45 million years. But one surprising finding was that ocean cooling did not always correspond to increases in Antarctic ice. Specifically for a 1 million year long period of ocean cooling from 25 to 24 million years ago. "We show that this is likely related to tectonic subsidence and the influx of relatively warm ocean water in the Ross Sea region," says Dr Bendle.

"We can see that ice in Antarctica is currently changing -- not least with the loss of some ice-shelves and cracks appearing recently in the Thwaites Glacier, one of the largest glaciers in the region. This new study of Earth's past is one of the clearest indications yet that humans continue to produce CO2 levels for which we can expect major ice loss at the Antarctic margins and global sea-level rise over the coming decades and centuries."

The team plan to continue to apply biomarker and machine learning approaches to reconstruct the climatic evolution of Antarctica and implications for future warming and sea-level rise.

Read more at Science Daily

Faster in the Past: New seafloor images of West Antarctic Ice Sheet upend understanding of Thwaites Glacier retreat

The Thwaites Glacier in West Antarctica -- about the size of Florida -- has been an elephant in the room for scientists trying to make global sea level rise predictions.

This massive ice stream is already in a phase of fast retreat (a "collapse" when viewed on geological timescales) leading to widespread concern about exactly how much, or how fast, it may give up its ice to the ocean.

The potential impact of Thwaites' retreat is spine-chilling: a total loss of the glacier and surrounding icy basins could raise sea level from three to 10 feet.

A new study in Nature Geoscience led by marine geophysicist Alastair Graham at the University of South Florida's College of Marine Science adds cause for concern. For the first time, scientists mapped in high-resolution a critical area of the seafloor in front of the glacier that gives them a window into how fast Thwaites retreated and moved in the past.

The stunning imagery shows geologic features that are new to science, and also provides a kind of crystal ball to see into Thwaites' future. In people and ice sheets alike, past behavior is key to understanding future behavior.

The team documented more than 160 parallel ridges that were created, like a footprint, as the glacier's leading edge retreated and bobbed up and down with the daily tides.

"It's as if you are looking at a tide gauge on the seafloor," Graham said. "It really blows my mind how beautiful the data are."

Beauty aside, what's alarming is that the rate of Thwaites' retreat that scientists have documented more recently are small compared to the fastest rates of change in its past, said Graham.

To understand Thwaites' past retreat, the team analyzed the rib-like formations submerged 700 meters (just under half a mile) beneath the polar ocean and factored in the tidal cycle for the region, as predicted by computer models, to show that one rib must have been formed every single day.

At some point in the last 200 years, over a duration of less than six months, the front of the glacier lost contact with a seabed ridge and retreated at a rate of more than 2.1 kilometers per year (1.3 miles per year) -- twice the rate documented using satellites between 2011 and 2019.

"Our results suggest that pulses of very rapid retreat have occurred at Thwaites Glacier in the last two centuries, and possibly as recently as the mid-20th Century," Graham said.

"Thwaites is really holding on today by its fingernails, and we should expect to see big changes over small timescales in the future-even from one year to the next-once the glacier retreats beyond a shallow ridge in its bed," said marine geophysicist and study co-author Robert Larter from the British Antarctic Survey.

To collect the imagery and supporting geophysical data, the team, which included scientists from the United States, the United Kingdom and Sweden, launched a state-of-the-art orange robotic vehicle loaded with imaging sensors called 'Rán'from the R/V Nathaniel B. Palmer during an expedition in 2019.

Rán, operated by scientists at the University of Gothenburg in Sweden, embarked on a 20-hour mission that was as risky as it was serendipitous, Graham said. It mapped an area of the seabed in front of the glacier about the size of Houston -- and did so in extreme conditions during an unusual summer notable for its lack of sea ice.

This allowed scientists to access the glacier front for the first time in history.

"This was a pioneering study of the ocean floor, made possible by recent technological advancements in autonomous ocean mapping and a bold decision by the Wallenberg foundation to invest into this research infrastructure," said Anna Wåhlin, a physical oceanographer from the University of Gothenburg who deployed Rán at Thwaites. "The images Ran collected give us vital insights into the processes happening at the critical junction between the glacier and the ocean today."

"It was truly a once in a lifetime mission," said Graham, who said the team would like to sample the seabed sediments directly so they can more accurately date the ridge-like features.

"But the ice closed in on us pretty quickly and we had to leave before we could do that on this expedition," he said.

While many questions remain, one thing's for sure: It used to be that scientists thought of the Antarctic ice sheets as sluggish and slow to respond, but that's simply not true, said Graham.

"Just a small kick to Thwaites could lead to a big response," he said.

According to the United Nations, roughly 40 percent of the human population lives within 60 miles of the coast.

"This study is part of a cross-disciplinary collective effort to understand the Thwaites Glacier system better," said Tom Frazer, dean of the USF College of Marine Science, "and just because it's out of sight, we can't have Thwaites out of mind. This study is an important step forward in providing essential information to inform global planning efforts."

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Hidden in caves: Mineral overgrowths reveal 'unprecedented' sea level rise

The early 1900s were an exciting time across the world, with rapid advances in the steel, electric and automobile industries. The industrial changes also mark an inflection point in our climate. According to an international team of researchers led by the University of South Florida (USF), the sea level has risen 18 centimeters since the start of the 20th century.

The study, featured on the cover of the July 1 issue of Science Advances, works to identify preindustrial sea levels and examines the impact of modern greenhouse warming on sea-level rise.

The team, which includes USF graduate students, traveled to Mallorca, Spain -- home to more than 1,000 cave systems, some of which have deposits that formed millions of years ago. For this study, they focused on analyzing deposits from 4,000 years ago to present day.

The team found evidence of a previously unknown 20 centimeter sea-level rise that occurred nearly 3,200 years ago when ice caps melted naturally over the course of 400 years at a rate of 0.5 millimeters per year. Otherwise, despite major climatic events like Medieval Warm Period and the Little Ice Age, the sea level remained exceptionally stable until 1900.

"The results reported in our study are alarming," said lead author Bogdan P. Onac, geology professor at USF. "The sea-level rise since the 1900s is unprecedented when compared to the natural change in ice volumes over the last 4,000 years. This implies that if global temperatures continue to rise, sea levels could eventually reach higher levels than scientists previously estimated."

To create the timeline, the team gathered 13 samples from eight caves along the coastline of the Mediterranean Sea. The deposits are rare -- only forming near the coastline in cave passages that were repeatedly flooded by sea water, making them accurate markers of sea-level changes overtime. Each deposit holds valuable insight into both the past and future, helping researchers determine how quickly the sea level will rise in the coming decades and centuries.

The samples were taken to the University of New Mexico and University of Bern in Switzerland, where special instruments were used to determine their age by uranium-series method. Over time, uranium decays into other elements such as thorium and lead, allowing researchers to create a timeline of the sea level documented in each deposit.

A complex software at Harvard University helped generate predictions using various ice models and Earth's parameters to showcase an accurate history of the sea level. These predictions are essential because they allow researchers to estimate past global mean sea level, which is key in addressing future sea-level rise.

"If humans continue to be the main driver and the temperature increases 1.5 degrees in the near future, there will be irreversible damage," Onac said. "There will be no turning back from that point on."

Based on ice mass loss from the Antarctic and Greenland, the average sea-level rise since 2008 is 1.43 millimeters per year.

Permanent flooding from the rising sea level won't happen overnight, but Onac says it will be seen more and more during storm surges and hurricanes. With nearly 40 percent of the world's population living within 62 miles of a coast, the rising sea level could be catastrophic with substantial societal and economic impacts.

"Even if we stop right now, sea level will continue to rise for at least a couple of decades, if not centuries, simply because the system is warmed up."

In June, Onac received a new research grant from the National Science Foundation to continue his research to predict future sea-level rise due to global warming. The grant will allow Onac to expand the research further into history by 130,000 years and create a better understanding of sea level globally. Starting in September, Onac and his team will begin analyzing cave deposits from around the globe, including Italy, Greece, Mexico and Cuba.

Read more at Science Daily

New link between greenhouse gasses and sea level rise

A new study provides the first evidence that rising greenhouse gases have a long-term warming effect on the Amundsen Sea in West Antarctica. Scientists from British Antarctic Survey (BAS) say that while others have proposed this link, no one has been able to demonstrate it.

Ice loss from the West Antarctic Ice Sheet in the Amundsen Sea is one of the fastest growing and most concerning contributions to global sea level rise. If the West Antarctic Ice Sheet were to melt, global sea levels could rise by up to three metres. The patterns of ice loss suggest that the ocean may have been warming in the Amundsen Sea over the past one hundred years, but scientific observations of the region only began in 1994.

In the study -- published in the journal Geophysical Research Letters -- oceanographers used advanced computer modelling to simulate the response of the ocean to a range of possible changes in the atmosphere between 1920-2013.

The simulations show the Amundsen Sea generally became warmer over the century. This warming corresponds with simulated trends in wind patterns in the region which increase temperatures by driving warm water currents towards and beneath the ice. Rising greenhouse gases are known to make these wind patterns more likely, and so the trend in winds is thought to be caused in part by human activity.

This study supports theories that ocean temperatures in the Amundsen Sea have been rising since before records began. It also provides the missing link between ocean warming and wind trends which are known to be partly driven by greenhouse gasses. Ocean temperatures around the West Antarctic Ice Sheet will probably continue to rise if greenhouse gas emissions increase, with consequences for ice melt and global sea levels. These findings suggest, however, that this trend could be curbed if emissions are sufficiently reduced and wind patterns in the region are stabilised.

Dr Kaitlin Naughten, ocean-ice modeller at BAS and lead author of this study, says,

"Our simulations show how the Amundsen Sea responds to long-term trends in the atmosphere, specifically the Southern Hemisphere westerly winds. This raises concerns for the future because we know these winds are affected by greenhouse gases. However, it should also give us hope, because it shows that sea level rise is not out of our control."

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Rapid glacial advance reconstructed during the time of Norse occupation in Greenland

The Greenland Ice Sheet is the second largest ice body in the world, and it has the potential to contribute significantly to global sea-level rise in a warming global climate. Understanding the long-term record of the Greenland Ice Sheet, including both records of glacial advance and retreat, is critical in validating approaches that model future ice-sheet scenarios. However, this reconstruction can be extremely challenging. A new study published Thursday in the journal Geology reconstructed the advance of one of the largest tidewater glaciers in Greenland to provide a better understanding of long-term glacial dynamics.

"In the news, we're very used to hearing about glacial retreat, and that's because in a warming climate scenario -- which is what we're in at the moment -- we generally document ice masses retreating. However, we also want to understand how glaciers react if there is a climate cooling and subsequent advance. To do this, we need to reconstruct glacier geometry from the past," said Danni Pearce, co-lead author of the study.

An interdisciplinary team of researchers studied the advance of Kangiata Nunaata Sermia (KNS) -- the largest tidewater glacier in southwest Greenland -- during a period of cooling when the Norse had settlements in Greenland. Differing from glaciers that are strictly on land, tidewater glaciers extend and flow all the way to the ocean or a sea, where they can then calve and break up into icebergs.

Reconstructing the advance of glaciers can be exceptionally difficult, because the glacier typically destroys or reworks everything in its path as it advances forward. The research team undertook multiple field seasons in Greenland, traveling on foot to remote sites -- many of which hadn't been visited since the 1930s -- to try and uncover the record of KNS advance.

"When we went out into the field, we had absolutely no idea whether the evidence would be there or not, so I was incredibly nervous. Though we did a huge amount of planning beforehand, until you go out into the field you don't know what you're going to find," said James Lea, the other co-lead author of the study.

By traveling on foot, the research team was able to more closely examine and explore sites that otherwise may have been missed if traveling by helicopter. The team's planning paid off, and the sedimentary sequences they studied and sampled held the clues they were looking for to date and track the advance of the glacier.

The research team found that during the twelfth and thirteenth centuries CE, KNS advanced at least 15 km, at a rate of ~115 m/yr. This rate of advance is comparable to modern rates of glacial retreat observed over the past ~200 years, indicating that when climate is cooler glaciers can advance equally as fast as they are currently retreating. The glacier reached its maximum extent by 1761 CE during the Little Ice Age, culminating in a total advance of ~20 km. Since then, KNS has retreated ~23 km to its present position.

The period when the glacier was advancing coincided with when the Norse were present in Greenland. Prior to its maximum extent during the Little Ice Age, the researchers found that KNS advanced to a location within only 5 km of a Norse farmstead.

"Even though KNS was rapidly coming down the fjord, it did not seem to affect the Norse, which we found really unusual," said Pearce. "So the team started to think about the surrounding environment and the amount of iceberg production in the fjord during that time. At the moment, the fjord is completely filled with icebergs, making boat access challenging, and we know from historical record that it has been like this for the last 200 years while the glacier has been retreating. However, for KNS to advance at 115 m/yr, it needed to hang onto its ice and could not have been producing a lot of icebergs. So we actually think that the fjord would have looked very different with few icebergs, which allowed the Norse far more easy access to this site for farming, hunting, and fishing."

In the 1930s, archaeologists who visited the site hypothesized that conditions in the fjord must have been different from the present day in order for the Norse to have occupied the site, and this current research study provides data to support these long-held ideas.

"So we have this counterintuitive notion that climate cooling and glacier advance might have actually helped the Norse in this specific circumstance and allowed them to navigate more of the fjord more easily," said Lea.

The Norse left Greenland during the fifteenth century CE, and these results are consistent with the idea that a cooling climate was likely not the cause of their exodus; rather, a combination of economic factors likely led the Norse to abandon Greenland.

The results from this research reconstructing rapid glacial advance are also shown to be consistent with the ways ice sheet models work, which brings confidence to the projections from these models. Having accurate models and projections are crucial in understanding and preparing for future scenarios of continued retreat of the Greenland Ice Sheet and associated sea-level rise.

"Melt from Greenland not only impacts sea-level change but also the ecology around the ice sheets, fisheries, the biological productivity of the oceans -- how much algae is growing. And also because the types of glaciers we're looking at produce icebergs these can cause hazards to shipping and trade, especially if the Northwest Passage opens up as it is expected to," said James Lea.

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U.S. coastline to see up to a foot of sea level rise by 2050

The United States is expected to experience as much sea level rise by the year 2050 as it witnessed in the previous hundred years. That's according to a NOAA-led report updating sea level rise decision-support information for the U.S. released in partnership with half a dozen other federal agencies.

The Sea Level Rise Technical Report provides the most up-to-date sea level rise projections for all U.S. states and territories by decade for the next 100 years and beyond, based on a combination of tide gauge and satellite observations and all the model ensembles from the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). The report projects sea levels along the coastline will rise an additional 10-12 inches by 2050 with specific amounts varying regionally, mainly due to land height changes.

The report updates the federal government's 2017 sea level rise projections, and provides additional information on tide, wind, and storm-driven extreme water levels affecting current and future coastal flood risk. A suite of federal tools are using this data, including the NOAA Sea Level Rise Viewer, which are critical to the Administration's commitment to tackle the climate crisis by making actionable climate data accessible to those who need it.

"For businesses along the coast, knowing what to expect and how to plan for the future is critical," said U.S. Secretary of Commerce Gina M. Raimondo. "These updated projections will help businesses, and the communities they support, understand risks and make smart investments in the years ahead."

"This new data on sea rise is the latest reconfirmation that our climate crisis -- as the President has said -- is blinking 'code red,'" said Gina McCarthy, National Climate Advisor. "We must redouble our efforts to cut the greenhouse gases that cause climate change while, at the same time, help our coastal communities become more resilient in the face of rising seas."

"This is a global wake-up call and gives Americans the information needed to act now to best position ourselves for the future," said Rick Spinrad, Ph.D., NOAA Administrator. "As we build a Climate Ready Nation, these updated data can inform coastal communities and others about current and future vulnerabilities in the face of climate change and help them make smart decisions to keep people and property safe over the long run."

The report also finds that the sea level rise expected by 2050 will create a profound increase in the frequency of coastal flooding, even in the absence of storms or heavy rainfall.

"By 2050, moderate flooding ⁠ -- which is typically disruptive and damaging by today's weather, sea level and infrastructure standards ⁠ -- is expected to occur more than 10 times as often as it does today," said Nicole LeBoeuf, NOAA National Ocean Service Director. "These numbers mean a change from a single event every 2-5 years to multiple events each year, in some places."

"This report supports previous studies and confirms what we have long known: Sea levels are continuing to rise at an alarming rate, endangering communities around the world. Science is indisputable and urgent action is required to mitigate a climate crisis that is well underway," said Bill Nelson, NASA Administrator. "NASA is steadfast in our commitment to protecting our home planet by expanding our monitoring capabilities and continuing to ensure our climate data is not only accessible but understandable."

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Hidden mangrove forest in the Yucatan peninsula reveals ancient sea levels

Deep in the heart of the Yucatan Peninsula, an ancient mangrove ecosystem flourishes more than 200 kilometers (124 miles) from the nearest ocean. This is unusual because mangroves -- salt-tolerant trees, shrubs, and palms -- are typically found along tropical and subtropical coastlines.

A new study led by researchers across the University of California system in the United States and researchers in Mexico focuses on this luxuriant red mangrove forest. This "lost world" is located far from the coast along the banks of the San Pedro Martir River, which runs from the El Petén rainforests in Guatemala to the Balancán region in Tabasco, Mexico.

Because the red mangrove (Rhizophora mangle) and other species present in this unique ecosystem are only known to grow in salt water or somewhat salty water, the binational team set out to discover how the coastal mangroves were established so deep inland in fresh water completely isolated from the ocean. Their findings were published Oct. 4 in the Proceedings of the National Academy of Sciences.

Integrating genetic, geologic, and vegetation data with sea-level modeling, the study provides a first glimpse of an ancient coastal ecosystem. The researchers found that the San Pedro mangrove forests reached their current location during the last interglacial period, some 125,000 years ago, and have persisted there in isolation as the oceans receded during the last glaciation.

The study provides a snapshot of the global environment during the last interglacial period, when the Earth became very warm and polar ice caps melted entirely, making global sea levels much higher than they are today.

"The most amazing part of this study is that we were able to examine a mangrove ecosystem that has been trapped in time for more than 100,000 years," said study co-author Octavio Aburto-Oropeza, a marine ecologist at Scripps Institution of Oceanography at UC San Diego and a PEW Marine Fellow. "There is certainly more to discover about how the many species in this ecosystem adapted throughout different environmental conditions over the past 100,000 years. Studying these past adaptations will be very important for us to better understand future conditions in a changing climate."

Combining multiple lines of evidence, the study demonstrates that the rare and unique mangrove ecosystem of the San Pedro River is a relict -- that is, organisms that have survived from an earlier period -- from a past warmer world when relative sea levels were six to nine meters (20 to 30 feet) higher than at present, high enough to flood the Tabasco lowlands of Mexico and reach what today are tropical rainforests on the banks of the San Pedro River.

The study highlights the extensive landscape impacts of past climate change on the world's coastlines and shows that during the last interglacial, much of the Gulf of Mexico coastal lowlands were under water. Aside from providing an important glimpse of the past and revealing the changes suffered by the Mexican tropics during the ice ages, these findings also open opportunities to better understand future scenarios of relative sea-level rise as climate change progresses in a human-dominated world.

Carlos Burelo, a botanist at the Universidad Juárez Autónoma de Tabasco and a native of the region, drew the attention of the rest of the team towards the existence of this relict ecosystem in 2016. "I used to fish here and play on these mangroves as a kid, but we never knew precisely how they got there," said Burelo. "That was the driving question that brought the team together."

Burelo's field work and biodiversity surveys in the region established the solid foundation of the study. His remarkable discovery of the ancient ecosystem is documented in "Memories of the Future: the modern discovery of a relict ecosystem," anaward-winning short film produced by Scripps alumnus Ben Fiscella Meissner (MAS MBC '17).

Felipe Zapata and Claudia Henriquez of UCLA led the genetic work to estimate the origin and age of the relict forest. Sequencing segments of the genomes of the red mangrove trees, they were able to establish that this ecosystem migrated from the coasts of the Gulf of Mexico into the San Pedro River over 100,000 years ago and stayed there in isolation after the ocean receded when temperatures dropped. While mangroves are the most notable species in the forest, they found nearly 100 other smaller species that also have a lineage from the ocean.

"This discovery is extraordinary," said Zapata. "Not only are the red mangroves here with their origins printed in their DNA, but the whole coastal lagoon ecosystem of the last interglacial has found refuge here."

Paula Ezcurra, science program manager at the Climate Science Alliance, carried out the sea-level modeling, noting that the coastal plains of the southern Gulf of Mexico lie so low that a relatively small change in sea level can produce dramatic effects inland. She said a fascinating piece of this study is how it highlights the benefits of working collaboratively among scientists from different disciplines.

"Each piece of the story alone is not sufficient, but when taken together, the genetics, geology, botany, and field observations tell an incredible story. Each researcher involved lent their expertise that allowed us to uncover the mystery of a 100,000+ year-old forest," said Ezcurra, an alumna of Scripps Oceanography (MAS CSP '17).

The field work was led by the ecologists on the team -- Octavio Aburto-Oropeza, Paula Ezcurra, Exequiel Ezcurra of UC Riverside, and Sula Vanderplank of Pronatura Noroeste. Visiting the study sites several times starting in 2016, they collected rocks, sediments and fossils to analyze in the lab, helping them pinpoint evidence from the past that is consistent with a marine environment.

The authors note that the region surrounding the study sites was systematically deforested in the 1970s by a misguided development plan; the banks of the San Pedro River were only spared because the bulldozers could not reach it. The area is still threatened by human activities, so the researchers stressed the need to protect this biologically important area in the future.

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Climate change widespread, rapid, and intensifying: IPCC

Scientists are observing changes in the Earth's climate in every region and across the whole climate system, according to the latest Intergovernmental Panel on Climate Change (IPCC) Report, released today. Many of the changes observed in the climate are unprecedented in thousands, if not hundreds of thousands of years, and some of the changes already set in motion -- such as continued sea level rise -- are irreversible over hundreds to thousands of years.

However, strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change. While benefits for air quality would come quickly, it could take 20-30 years to see global temperatures stabilize, according to the IPCC Working Group I report, Climate Change 2021: the Physical Science Basis, approved on Friday by 195 member governments of the IPCC, through a virtual approval session that was held over two weeks starting on July 26.

The Working Group I report is the first installment of the IPCC's Sixth Assessment Report (AR6), which will be completed in 2022.

"This report reflects extraordinary efforts under exceptional circumstances," said Hoesung Lee, Chair of the IPCC. "The innovations in this report, and advances in climate science that it reflects, provide an invaluable input into climate negotiations and decision-making."

Faster warming

The report provides new estimates of the chances of crossing the global warming level of 1.5°C in the next decades, and finds that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will be beyond reach.

The report shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1°C of warming since 1850-1900, and finds that averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of warming. This assessment is based on improved observational datasets to assess historical warming, as well progress in scientific understanding of the response of the climate system to human-caused greenhouse gas emissions.

"This report is a reality check," said IPCC Working Group I Co-Chair Valérie Masson-Delmotte. "We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare."

Every region facing increasing changes

Many characteristics of climate change directly depend on the level of global warming, but what people experience is often very different to the global average. For example, warming over land is larger than the global average, and it is more than twice as high in the Arctic.

"Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming," said IPCC Working Group I Co-Chair Panmao Zhai.

The report projects that in the coming decades climate changes will increase in all regions. For 1.5°C of global warming, there will be increasing heat waves, longer warm seasons and shorter cold seasons. At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the report shows.

But it is not just about temperature. Climate change is bringing multiple different changes in different regions -- which will all increase with further warming. These include changes to wetness and dryness, to winds, snow and ice, coastal areas and oceans. For example:
 

• Climate change is intensifying the water cycle. This brings more intense rainfall and associated flooding, as well as more intense drought in many regions.
• Climate change is affecting rainfall patterns. In high latitudes, precipitation is likely to increase, while it is projected to decrease over large parts of the subtropics. Changes to monsoon precipitation are expected, which will vary by region.
• Coastal areas will see continued sea level rise throughout the 21st century, contributing to more frequent and severe coastal flooding in low-lying areas and coastal erosion. Extreme sea level events that previously occurred once in 100 years could happen every year by the end of this century.
• Further warming will amplify permafrost thawing, and the loss of seasonal snow cover, melting of glaciers and ice sheets, and loss of summer Arctic sea ice.
• Changes to the ocean, including warming, more frequent marine heatwaves, ocean acidification, and reduced oxygen levels have been clearly linked to human influence. These changes affect both ocean ecosystems and the people that rely on them, and they will continue throughout at least the rest of this century.
• For cities, some aspects of climate change may be amplified, including heat (since urban areas are usually warmer than their surroundings), flooding from heavy precipitation events and sea level rise in coastal cities.

For the first time, the Sixth Assessment Report provides a more detailed regional assessment of climate change, including a focus on useful information that can inform risk assessment, adaptation, and other decision-making, and a new framework that helps translate physical changes in the climate -- heat, cold, rain, drought, snow, wind, coastal flooding and more -- into what they mean for society and ecosystems.

This regional information can be explored in detail in the newly developed Interactive Atlas https://interactive-atlas.ipcc.ch/ as well as regional fact sheets, the technical summary, and underlying report.

Human influence on the past and future climate

"It has been clear for decades that the Earth's climate is changing, and the role of human influence on the climate system is undisputed," said Masson-Delmotte. Yet the new report also reflects major advances in the science of attribution -- understanding the role of climate change in intensifying specific weather and climate events such as extreme heat waves and heavy rainfall events.

The report also shows that human actions still have the potential to determine the future course of climate. The evidence is clear that carbon dioxide (CO2) is the main driver of climate change, even as other greenhouse gases and air pollutants also affect the climate.

"Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate," said Zhai.

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Evidence of Antarctic glacier's tipping point confirmed

 Researchers have confirmed for the first time that Pine Island Glacier in West Antarctica could cross tipping points, leading to a rapid and irreversible retreat which would have significant consequences for global sea level.

Pine Island Glacier is a region of fast-flowing ice draining an area of West Antarctica approximately two thirds the size of the UK. The glacier is a particular cause for concern as it is losing more ice than any other glacier in Antarctica.

Currently, Pine Island Glacier together with its neighbouring Thwaites glacier are responsible for about 10% of the ongoing increase in global sea level.

Scientists have argued for some time that this region of Antarctica could reach a tipping point and undergo an irreversible retreat from which it could not recover. Such a retreat, once started, could lead to the collapse of the entire West Antarctic Ice Sheet, which contains enough ice to raise global sea level by over three metres.

While the general possibility of such a tipping point within ice sheets has been raised before, showing that Pine Island Glacier has the potential to enter unstable retreat is a very different question.

Now, researchers from Northumbria University have shown, for the first time, that this is indeed the case.

Their findings are published in leading journal, The Cryosphere.

Using a state-of-the-art ice flow model developed by Northumbria's glaciology research group, the team have developed methods that allow tipping points within ice sheets to be identified.

For Pine Island Glacier, their study shows that the glacier has at least three distinct tipping points. The third and final event, triggered by ocean temperatures increasing by 1.2C, leads to an irreversible retreat of the entire glacier.

The researchers say that long-term warming and shoaling trends in Circumpolar Deep Water, in combination with changing wind patterns in the Amundsen Sea, could expose Pine Island Glacier's ice shelf to warmer waters for longer periods of time, making temperature changes of this magnitude increasingly likely.

The lead author of the study, Dr Sebastian Rosier, is a Vice-Chancellor's Research Fellow in Northumbria's Department of Geography and Environmental Sciences. He specialises in the modelling processes controlling ice flow in Antarctica with the goal of understanding how the continent will contribute to future sea level rise.

Dr Rosier is a member of the University's glaciology research group, led by Professor Hilmar Gudmundsson, which is currently working on a major £4million study to investigate if climate change will drive the Antarctic Ice Sheet towards a tipping point.

Dr Rosier explained: "The potential for this region to cross a tipping point has been raised in the past, but our study is the first to confirm that Pine Island Glacier does indeed cross these critical thresholds.

"Many different computer simulations around the world are attempting to quantify how a changing climate could affect the West Antarctic Ice Sheet but identifying whether a period of retreat in these models is a tipping point is challenging.

"However, it is a crucial question and the methodology we use in this new study makes it much easier to identify potential future tipping points."

Hilmar Gudmundsson, Professor of Glaciology and Extreme Environments worked with Dr Rosier on the study. He added: "The possibility of Pine Island Glacier entering an unstable retreat has been raised before but this is the first time that this possibility is rigorously established and quantified.

"This is a major forward step in our understanding of the dynamics of this area and I'm thrilled that we have now been able to finally provide firm answers to this important question.

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Early Earth's hot mantle may have led to Archean 'water world'

 A vast global ocean may have covered early Earth during the early Archean eon, 4 to 3.2 billion years ago, a side effect of having a hotter mantle than today, according to new research.

The new findings challenge earlier assumptions that the size of the Earth's global ocean has remained constant over time and offer clues to how its size may have changed throughout geologic time, according to the study's authors.

Most of Earth's surface water exists in the oceans. But there is a second reservoir of water deep in Earth's interior, in the form of hydrogen and oxygen attached to minerals in the mantle.

A new study in AGU Advances, which publishes high-impact, open-access research and commentary across the Earth and space sciences, estimates how much water the mantle potentially could hold today and how much water it could have stored in the past.

The findings suggest that, since early Earth was hotter than it is today, its mantle may have contained less water because mantle minerals hold onto less water at higher temperatures. Assuming that the mantle currently has more than 0.3-0.8 times the mass of the ocean, a larger surface ocean might have existed during the early Archean. At that time, the mantle was about 1,900-3,000 degrees Kelvin (2,960-4,940 degrees Fahrenheit), compared to 1,600-2,600 degrees Kelvin (2,420-4,220 degrees Fahrenheit) today.

If early Earth had a larger ocean than today, that could have altered the composition of the early atmosphere and reduced how much sunlight was reflected back into space, according to the authors. These factors would have affected the climate and the habitat that supported the first life on Earth.

"It's sometimes easy to forget that the deep interior of a planet is actually important to what's going on with the surface," said Rebecca Fischer, a mineral physicist at Harvard University and co-author of the new study. "If the mantle can only hold so much water, it's got to go somewhere else, so what's going on thousands of kilometers below the surface can have pretty big implications."

Earth's sea level has remained fairly constant during the last 541 million years. Sea levels from earlier in Earth's history are more challenging to estimate, however, because little evidence has survived from the Archean eon. Over geologic time, water can move from the surface ocean to the interior through plate tectonics, but the size of that water flux is not well understood. Because of this lack of information, scientists had assumed the global ocean size remained constant over geologic time.

In the new study, co-author Junjie Dong, a mineral physicist at Harvard University, developed a model to estimate the total amount of water that Earth's mantle could potentially store based on its temperature. He incorporated existing data on how much water different mantle minerals can store and considered which of these 23 minerals would have occurred at different depths and times in Earth's past. He and his co-authors then related those storage estimates to the volume of the surface ocean as Earth cooled.

Jun Korenaga, a geophysicist at Yale University who was not involved in the research, said this is the first time scientists have linked mineral physics data on water storage in the mantle to ocean size. "This connection has never been raised in the past," he said.

Dong and Fischer point out that their estimates of the mantle's water storage capacity carry a lot of uncertainty. For example, scientists don't fully understand how much water can be stored in bridgmanite, the main mineral in the mantle.

The new findings shed light on how the global ocean may have changed over time and can help scientists better understand the water cycles on Earth and other planets, which could be valuable for understanding where life can evolve.

"It is definitely useful to know something quantitative about the evolution of the global water budget," said Suzan van der Lee, a seismologist at Northwestern University who did not participate in the study. "I think this is important for nitty-gritty seismologists like myself, who do imaging of current mantle structure and estimate its water content, but it's also important for people hunting for water-bearing exoplanets and asking about the origins of where our water came from."

Dong and Fischer are now using the same approach to calculate how much water may be held inside Mars.

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Greenland ice sheet faces irreversible melting

 

Illustration of northern Canada and Greenland from space.

In a study published this week in The Cryosphere, researchers from the National Centre for Atmospheric Science and University of Reading demonstrate how climate change could lead to irreversible sea level rise as temperatures continue to rise and the Greenland ice sheet continues to decline.

The massive ice sheet faces a point of no return, beyond which it will no longer fully regrow, permanently changing sea levels around the world.

The Greenland ice sheet is seven times the area of the UK, and stores a large amount of the Earth's frozen water. At current rates of melting, it contributes almost 1mm to sea level per year, and accounts for around a quarter of total sea level rise.

Since 2003, despite seasonal periods of growth, Greenland's ice sheet has lost three and a half trillion tonnes of ice.

Rising sea levels are one of the most severe effects of climate change, threatening coastal areas around the world, and putting millions of people who live in low-lying areas at risk. Bangladesh, Florida, and eastern England are among many areas known to be particularly vulnerable.

Under scenarios in which global warming goes beyond 2°C, the Paris Agreement target, we should expect significant ice loss and several metres of global sea level rise to persist for tens of thousands of years, according to the new research. The warmer the climate, the greater the sea-level rise.

In addition, even if temperatures later return to current levels, scientists have shown that the Greenland ice sheet will never fully regrow once it melts beyond a critical point. After that point, sea levels would permanently remain two meters higher than now, regardless of other factors contributing to sea level rise.

This is because the ice sheet is so large that it has a substantial impact on its local climate, and as it declines, Greenland would experience warmer temperatures and less snowfall.

Once the ice-sheet retreats from the Northern part of the island, the area would remain ice-free.

To avoid the irreversible sea level rise the melting would cause, scientists say that climate change must be reversed before the ice sheet has declined to the threshold mass, which would be reached in about 600 years at the highest rate of mass loss within the likely range of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

Professor Jonathan Gregory, Climate Scientist from the National Centre for Atmospheric Science and University of Reading, said: "Our experiments underline the importance of mitigating global temperature rise. To avoid partially irreversible loss of the ice sheet, climate change must be reversed -- not just stabilised -- before we reach the critical point where the ice sheet has declined too far."

To study the ice-sheet, scientists from the National Centre for Atmospheric Science simulated the effects of Greenland ice sheet melting under a range of possible temperature rises, ranging from minimal warming to worst-case scenarios.

Under all future climates like the present or warmer, the ice-sheet declined in size and contributed to some degree of sea-level rise.

Importantly, there were scenarios in which the ice sheet melting could be reversed. But, they rely on actions to counteract global warming before it's too late.

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Greenland is on track to lose ice faster than in any century over 12,000 years

 If human societies don't sharply curb emissions of greenhouse gases, Greenland's rate of ice loss this century is likely to greatly outpace that of any century over the past 12,000 years, a new study concludes.

The research will be published on Sept. 30 in the journal Nature. The study employs ice sheet modeling to understand the past, present and future of the Greenland Ice Sheet. Scientists used new, detailed reconstructions of ancient climate to drive the model, and validated the model against real-world measurements of the ice sheet's contemporary and ancient size.

The findings place the ice sheet's modern decline in historical context, highlighting just how extreme and unusual projected losses for the 21st century could be, researchers say.

"Basically, we've altered our planet so much that the rates of ice sheet melt this century are on pace to be greater than anything we've seen under natural variability of the ice sheet over the past 12,000 years. We'll blow that out of the water if we don't make severe reductions to greenhouse gas emissions," says Jason Briner, PhD, professor of geology in the University at Buffalo College of Arts and Sciences. Briner led the collaborative study, coordinating the work of scientists from multiple disciplines and institutions.

"If the world goes on a massive energy diet, in line with a scenario that the Intergovernmental Panel on Climate Change calls RCP2.6, our model predicts that the Greenland Ice Sheet's rate of mass loss this century will be only slightly higher than anything experienced in the past 12,000 years," Briner adds. "But, more worrisome, is that under a high-emissions RCP8.5 scenario -- the one the Greenland Ice Sheet is now following -- the rate of mass loss could be about four times the highest values experienced under natural climate variability over the past 12,000 years."

He and colleagues say the results reiterate the need for countries around the world to take action now to reduce emissions, slow the decline of ice sheets, and mitigate sea level rise. The research was largely funded by the U.S. National Science Foundation.

Combining ice sheet modeling with field work, real-life observations

The study brought together climate modelers, ice core scientists, remote sensing experts and paleoclimate researchers at UB, NASA's Jet Propulsion Laboratory (JPL), the University of Washington (UW), Columbia University's Lamont-Doherty Earth Observatory (LDEO), the University of California, Irvine (UCI) and other institutions.

This multidisciplinary team used a state-of-the-art ice sheet model to simulate changes to the southwestern sector of the Greenland Ice Sheet, starting from the beginning of the Holocene epoch some 12,000 years ago and extending forward 80 years to 2100.

Scientists tested the model's accuracy by comparing results of the model's simulations to historical evidence. The modeled results matched up well with data tied to actual measurements of the ice sheet made by satellites and aerial surveys in recent decades, and with field work identifying the ice sheet's ancient boundaries.

Though the project focused on southwestern Greenland, research shows that changes in the rates of ice loss there tend to correspond tightly with changes across the entire ice sheet.

"We relied on the same ice sheet model to simulate the past, the present and the future," says co-author Jessica Badgeley, a PhD student in the UW Department of Earth and Space Sciences. "Thus, our comparisons of the ice sheet mass change through these time periods are internally consistent, which makes for a robust comparison between past and projected ice sheet changes."

"We have significantly improved our understanding of how anomalous future Greenland change will be," says co-author Joshua Cuzzone, PhD, an assistant project scientist at UCI who completed much of his work on the study as a postdoctoral researcher at JPL and UCI. "This work represents a massive success for multidisciplinary science and collaboration, and represents a framework for future successful multidisciplinary work."

Cuzzone and other researchers at UCI and JPL led ice sheet modeling, leveraging the work of colleagues at UW, who used data from ice cores to create maps of temperatures and precipitation in the study region that were used to drive the ice sheet model simulations up to the year 1850. Previously published climate data was used to drive the simulations after that date.

UB and LDEO scientists partnered on field work that helped validate the model by identifying the ice sheet's boundaries in southwestern Greenland thousands of years ago.

"We built an extremely detailed geologic history of how the margin of the southwestern Greenland Ice Sheet moved through time by measuring beryllium-10 in boulders that sit on moraines," says co-author Nicolás Young, PhD, associate research professor at LDEO. "Moraines are large piles of debris that you can find on the landscape that mark the former edge of an ice sheet or glacier. A beryllium-10 measurement tells you how long that boulder and moraine have been sitting there, and therefore tells you when the ice sheet was at that exact spot and deposited that boulder.

"Amazingly, the model reproduced the geologic reconstruction really well. This gave us confidence that the ice sheet model was performing well and giving us meaningful results. You can model anything you want and your model will always spit out an answer, but we need some way to determine if the model is doing a good job."

A continuous timeline of changes to the Greenland Ice Sheet

The study makes an important contribution by creating a timeline of the past, present and future of the Greenland Ice Sheet, Briner says. The results are sobering.

"We have long timelines of temperature change, past to present to future, that show the influence of greenhouse gases on Earth's temperature," Briner says. "And now, for the first time, we have a long timeline of the impacts of that temperature -- in the form of Greenland Ice Sheet melt -- from the past to present to future. And what it shows is eye-opening."

"It is no secret that the Greenland Ice Sheet is in rough shape and is losing ice at an increasing rate," Young says. "But if someone wants to poke holes in this, they could simply ask, 'how do you know this isn't just part of the ice sheet's natural variability?' Well, what our study suggests is that the rate of ice loss for this century will exceed the rate of ice loss for any single century over the last 12,000 years. I think this is the first time that the current health of the Greenland Ice Sheet has been robustly placed into a long-term context."

Despite these sobering results, one vital takeaway from the model's future projections is that it's still possible for people and countries around the world to make an important difference by cutting emissions, Briner says. Models of the RCP2.6 and RCP8.5 scenarios yield very different results, with high-emission scenarios producing massive declines in the ice sheet's health, and significant sea level rise.

"Our findings are yet another wake-up call, especially for countries like the U.S.," Briner says. "Americans use more energy per person than any other nation in the world. Our nation has produced more of the CO2 that resides in the atmosphere today than any other country. Americans need to go on an energy diet. The most affluent Americans, who have the highest energy footprint, can afford to make lifestyle changes, fly less, install solar panels and drive an energy-efficient vehicle."

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Sea level rise from ice sheets track worst-case climate change scenario

 Ice sheets in Greenland and Antarctica whose melting rates are rapidly increasing have raised the global sea level by 1.8cm since the 1990s, and are matching the Intergovernmental Panel on Climate Change's worst-case climate warming scenarios.

According to a new study from the University of Leeds and the Danish Meteorological Institute, if these rates continue, the ice sheets are expected to raise sea levels by a further 17cm and expose an additional 16 million people to annual coastal flooding by the end of the century.

Since the ice sheets were first monitored by satellite in the 1990s, melting from Antarctica has pushed global sea levels up by 7.2mm, while Greenland has contributed 10.6mm. And the latest measurements show that the world's oceans are now rising by 4mm each year.

"Although we anticipated the ice sheets would lose increasing amounts of ice in response to the warming of the oceans and atmosphere, the rate at which they are melting has accelerated faster than we could have imagined," said Dr Tom Slater, lead author of the study and climate researcher at the Centre for Polar Observation and Modelling at the University of Leeds.

"The melting is overtaking the climate models we use to guide us, and we are in danger of being unprepared for the risks posed by sea level rise."

The results are published today in a study in the journal Nature Climate Change. It compares the latest results from satellite surveys from the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE) with calculations from climate models. The authors warn that the ice sheets are losing ice at a rate predicted by the worst-case climate warming scenarios in the last large IPCC report.

Dr Anna Hogg, study co-author and climate researcher in the School of Earth and Environment at Leeds, said: "If ice sheet losses continue to track our worst-case climate warming scenarios we should expect an additional 17cm of sea level rise from the ice sheets alone. That's enough to double the frequency of storm-surge flooding in many of the world's largest coastal cities."

So far, global sea levels have increased in the most part through a mechanism called thermal expansion, which means that volume of seawater expands as it gets warmer. But in the last five years, ice melt from the ice sheets and mountain glaciers has overtaken global warming as the main cause of rising sea levels.

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Antarctic ice walls protect the climate

Ice formation in Antarctica

Inland Antarctic ice contains volumes of water that can raise global sea levels by several metres. A new study published in the journal Nature shows that glacier ice walls are vital for the climate, as they prevent rising ocean temperatures and melting glacier ice.

The ocean can store much more heat than the atmosphere. The deep sea around Antarctica stores thermal energy that is the equivalent of heating the air above the continent by 400 degrees.

Now, a Swedish-led international research group has explored the physics behind the ocean currents close to the floating glaciers that surround the Antarctic coast.

"Current measurements indicate an increase in melting, particularly near the coast in some parts of Antarctica and Greenland. These increases can likely be linked to the warm, salty ocean currents that circulate on the continental shelf, melting the ice from below," says Anna Wåhlin, lead author of the study and professor of oceanography at the University of Gothenburg.

"What we found here is a crucial feedback process: the ice shelves are their own best protection against warm water intrusions. If the ice thins, more oceanic heat comes in and melts the ice shelf, which becomes even thinner etc. It is worrying, as the ice shelves are already thinning because of global air and ocean warming," says Céline Heuzé, climate researcher at the Department of Earth Sciences of Gothenburg University.

The stability of ice is a mystery

Inland Antarctic ice gradually moves towards the ocean. Despite the ice being so important, its stability remains a mystery -- as does the answer to what could make it melt faster.

Since the glaciers are difficult to access, researchers have been unable to find out much information about the active processes.

More knowledge has now been obtained from studying the measurement data collected from instruments that Anna Wåhlin and her researcher colleagues placed in the ocean around the Getz glacier in West Antarctica.

The ice's edge blocks warm seawater

Gertz has a floating section that is approximately 300 to 800 metres thick, beneath which there is seawater that connects to the ocean beyond. The glacier culminates in a vertical edge, a wall of ice that continues 300-400 metres down into the ocean. Warm seawater flows beneath this edge, towards the continent and the deeper ice further south.

"Studying the measurement data from the instruments, we found that the ocean currents are blocked by the ice edge. This limits the extent to which the warm water can reach the continent. We have long been stumped in our attempts to establish a clear link between the transport of warm water up on the continental shelf and melting glaciers.

Now, we understand that only a small amount of the current can make its way beneath the glacier. This means that around two-thirds of the thermal energy that travels up towards the continental shelf from the deep sea never reaches the ice."

Can lead to better prognoses

The results of the studies have provided researchers with a greater understanding of how these glacier areas work.

"From the Getz glacier, we are receiving measurements of heat transport in the ocean that correspond with the melting ice being measured by satellites. This also means that the floating glaciers -- the ice fronts in particular -- are key areas that should be closely monitored. If the ice walls were to disappear, much greater levels of thermal energy would be released towards the ice on land.

Consequently, we no longer expect to see a direct link between increasing westerly winds and growing levels of melting ice. Instead, the increased water levels can be caused by the processes that pump up warmer, heavier water to the continental shelf, for example as low-pressure systems move closer to the continent."

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