Greenland's ice sheet is melting -- and being replaced by vegetation

An estimated 11,000 sq miles or 28,707 sq kilometres of Greenland's ice sheet and glaciers have melted over the last three decades, according to a major analysis of historic satellite records.

The total area of ice loss is equivalent to the size of Albania, and represents about 1.6 % of Greenland's total ice and glacier cover.

Where there was once ice and snow, there is now barren rock, wetlands and areas of shrub.

A team of scientists from the University of Leeds, who have tracked the changes across Greenland from the 1980s through to the 2010s, say warmer air temperatures are causing the ice to retreat, which in turn is having an impact on the temperature of the land surface, greenhouse gas emissions and the stability of the landscape.

Permafrost -- a permanently frozen layer below the Earth's surface -- is being "degraded" by the warming and in some areas, the scientists warn that it could have an impact on the infrastructure, buildings and communities that exist above it.

Their findings -- "Land cover changes across Greenland dominated by a doubling of vegetation in three decades"- are reported today (13/02) in the journal Scientific Reports.

Impact of global warming

Greenland is part of the Arctic region. It is the world's biggest island, around 836,330 sq miles in size (2.1 million sq km). Most of the land is covered by ice and glaciers and it is home to almost 57,000 people.

Since the 1970s, the region has been warming at double the global mean rate. On Greenland, average annual air temperatures between 2007 and 2012 were 3 degrees C warmer, compared with the 1979 to 2000 average.

And the researchers warn that more extreme temperatures are likely in the future.

Jonathan Carrivick, an Earth scientist based in the Faculty of Environment at Leeds and one of the authors of the study, said: "Warmer temperatures are linked to the land cover changes that we are seeing on Greenland.

"By analysing high resolution satellite images, we have been able to produce a detailed record of the land cover changes that are taking place."

Ice disappears to be replaced by bare rock and shrubs

Ice loss was concentrated around the edges of present-day glaciers but also in the north and south- west of Greenland. There were also high-levels of ice loss in localised areas in the west, mid-north-west and south-east.

Over the three decades, the amount of land with vegetation growing on it increased by 33,774 sq miles (87,475 sq km), more than doubling over the study period.

A pronounced increase in vegetation was seen across the south-west, east and north-east. The greatest increase in dense wetland vegetation occurred in the vicinity of Kangerlussuaq in the south-west and in isolated areas in the north-east.

Analysis by the researchers revealed that vegetation had increased along a latitudinal gradient between 63 degrees North and 69 degrees North and declined north of this.

Jonathan Carrivick said: "We have seen signs that the loss of ice is triggering other reactions which will result in further loss of ice and further 'greening' of Greenland, where shrinking ice exposes bare rock that is then colonised by tundra and eventually shrub.

"At the same time, water released from the melting ice is moving sediment and silt, and that eventually forms wetlands and fenlands."

Loss of ice triggers further warming

The loss of ice affects land surface temperatures because of albedo, which is the measure of how reflective a surface is.

Snow and ice are good reflectors of the sun's energy hitting the Earth's surface and this helps to keep the Earth cooler. As the ice retreats, it exposes bedrock which absorbs more solar energy, raising the temperature of the land surface.

Similarly, as ice melts it increases the quantity of water in lakes. Water absorbs more solar energy than snow and this also increases the temperature of the land surface.

Greenhouse gas emitter

The analysis shows a near quadrupling of wetlands across Greenland, particularly in the east and north-east. The wetlands are a source of methane emissions.

Writing in the paper, the researchers noted: "Expansion of vegetation and especially in wetland areas indicates but also exacerbates permafrost thaw, active layer thickening and thus emissions of greenhouse gasespreviously stored in these Arctic soils."

The researchers also developed a model to predict those areas on Greenland that are likely to see "marked and accelerated" change in the future.

Dr Michael Grimes, the lead author of the report who conducted the research as part of their PhD, added: "The expansion of vegetation, occurring in tandem with the retreat of glaciers and the ice sheet, is significantly altering the flow of sediments and nutrients into coastal waters.

"These changes are critical, particularly for the indigenous populations whose traditional subsistence hunting practices rely on the stability of these delicate ecosystems.

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To restore ecosystems, think about thwarting hungry herbivores

Re-establishing plantings of trees, grasses and other vegetation is essential for restoring degraded ecosystems, but a new survey of almost 2,600 restoration projects from nearly every type of ecosystem on Earth finds that most projects fail to recognize and control one of the new plants' chief threats: hungry critters that eat plants.

"While most of the projects took steps to exclude competing plant species, only 10% took steps to control or temporarily exclude herbivores, despite the fact that in the early stages these plants are like lollipops -- irresistible little treats for grazers," said Brian Silliman, Rachel Carson Distinguished Professor of Marine Conservation Biology at Duke University's Nicholas School of the Environment.

By not protecting plants in their early states, conservationists are missing out on great opportunity to significantly speed restoration, improve its outcomes, and lower its costs, he said.

"Our analysis of the surveyed projects shows that introducing predators to keep herbivore populations in check or installing barriers to keep them at bay until plantings become more established and less vulnerable, can increase plant re-growth by 89% on average," said Silliman, who helped conceptualize the study and was one of its coauthors.

Those gains are equal to or greater than the gains realized by excluding competing plant species, the new survey shows.

"This begs the question: Why aren't we doing it more?" he asks.

The new survey was conducted with input from an international team of researchers affiliated with 20 universities and institutions. They published their peer-reviewed findings Nov. 3 in Science.

Qiang He, professor of coastal ecology at Fudan University and a former postdoctoral research associate of Silliman's at Duke, co-led the study with Changlin Xu, a member of He's Coastal Ecology Lab at Fudan.

The survey's findings have far-reaching implications for efforts to restore vegetation at a time of climate change, He said.

"Herbivores' effects were particularly pronounced in regions with higher temperatures and lower precipitation," He noted.

All of which leads to one inescapable conclusion, Silliman said.

"If we want more plants, we have to let more predators in or restore their populations," Silliman said. "Indeed, the decline of large predators, like wolves, lions, and sharks, that normally keep herbivore populations in check, is likely an important indirect cause of high grazing pressures."

"Conventional restoration is slowing our losses, but it's not expanding vegetation in many places, and climate change could make that even more difficult," he said.

Using predators to keep herbivores in check at restored sites is a relatively untapped approach that could help us boost plant diversity and restore ecosystems that are vital to human and environmental health, in less time and at lower costs," Silliman said. "It's like learning a new gardening trick that doubles your yield."

Once a planting is established, the herbivores are essential too, he added. "Plants just need a small break from being eaten to get restarted making ecosystems. Once they establish, herbivores are key to maintaining plant ecosystem diversity and function."

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How a massive North Atlantic cooling event disrupted early human occupation in Europe

A new study published in the journal Science finds that around 1.12 million years ago a massive cooling event in the North Atlantic and corresponding shifts in climate, vegetation and food resources disrupted early human occupation of Europe.

The study published by an international group of scientists from the UK, South Korea and Spain presents observational and modelling evidence documenting that unprecedented climate stress changed the course of early human history.

Archaic humans, known as Homo erectus moved from Africa into central Eurasia around 1.8 million years. From there on they spread towards western Europe, reaching the Iberian peninsula around 1.5 million years ago (Ma). Experiencing initially rather mild climatic conditions, these groups eventually established a foothold in southern Europe, as documented by several dated fossils and stone tools from this period. But given the increasing intensity of glacial cycles in Europe from 1.2 Ma onwards, it remains unknown for how long early humans lived in this area and whether the occupation was interrupted by worsening climate conditions.

To better understand the environmental conditions, which early human species in Europe experienced, the team of pollen experts, oceanographers, climate modelers, archeologists, and anthropologists combined data of a deep ocean sediment cores from the eastern subtropical Atlantic with new supercomputer climate model and human habitat model simulations covering the period of the depopulation event.

Sieving through thousands of small plant pollen stored in the ocean sediment core and analyzing preserved temperature-sensitive organic compounds left by tiny algae, which lived over a million years ago, the scientists discovered that around 1.127 million years ago, the climate over the eastern North Atlantic and the adjacent land suddenly cooled by 7oC.

"This massive cooling marks one of the first terminal stadial events in the paleoclimatic record. It occurred during the last phase of a glacial cycle, when ice-sheets disintegrated, releasing large amounts of freshwater into the ocean, and causing ocean circulation changes and a southward expansion of sea ice," says Prof. Chronis Tzedakis from University College London (UCL), senior author of the study.

The pollen data extracted from the ocean sediment core further add to this scenario "Rivers and winds bring tiny pollen from the adjacent land to the ocean, where they sink and get deposited in the deep ocean. According to our ocean sediment core pollen analysis, the North Atlantic cooling event switched western European vegetation to an inhospitable semi-desert landscape.," adds Dr. Vasiliki Margari from UCL, lead author of the study.

To quantify how early humans may have reacted to such an unprecedented climate anomaly, scientists from the IBS Center for Climate Physics (ICCP) in South Korea, conducted new computer model simulations for this period. By adding glacial freshwater to the North Atlantic, Dr. Kyung-Sook Yun, and Ms. Hyuna Kim from the ICCP were able to reproduce key features of the terminal stadial event, such as the cooling and drying over southern Europe. "We then used this global climate model simulation as an input for a human habitat model, which determines whether certain environmental conditions were suitable for early Homo erectus or not. We found that over many areas of southern Europe, early human species such as Homo erectus would have not been able to survive" describes Prof. Axel Timmermann, Director of the ICCP at Pusan National University and co-corresponding author of the study.

Even though the cooling event only lasted for about 4,000 years, a lack of stone tools and human remains over the next 200,000 years further raises the possibility of a long-lasting hiatus in European occupation. Europe was again repopulated around 900 thousand years ago by a group that is often referred to as Homo antecessor. This group and its descendants were much more resilient, because they were able to adapt to the increasing intensity of glacial conditions over Europe.

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Humidity may increase heat risk in urban climates

As temperatures across the globe reach record-level highs, urban areas are facing increased heat stress. Cities are generally warmer and dryer than adjacent rural land. But in the Global South, there is an additional complicating factor -- urban humid heat.

A new study, led by Yale School of the Environment scientists and published in Nature, investigated the combined effect of temperature and humidity on urban heat stress using observational data and an urban climate model calculation. Researchers found that the heat stress burden is dependent on local climate and a humidifying effect can erase the cooling benefits that would come from trees and vegetation.

"A widely held view is that urban residents suffer more heat burden than the general population owing to the urban heat island phenomenon. This view is incomplete because it omits another ubiquitous urban microclimate phenomenon called the urban dry island -- that urban land tends to be less humid than the surrounding rural land," says Xuhui Lee, Sara Shallenberger Brown Professor of Meteorology, who directed the study. "In dry, temperate, and boreal climates, urban residents are actually less heat-stressed than rural residents. But in the humid Global South, the urban heat island is dominant over the urban dry island, resulting in two to six extra dangerous heat stress days per summer."

Lee and YSE doctoral student Keer Zhang, lead author of the study, say they were motivated to investigate the issue for several reasons: a large percentage of the global population lives in urban areas; many people in informal urban settlements do not have access to air conditioning; and the problem is going to get worse as temperatures rise and more people move to cities. About 4.3 billion people, or 55% of the world's population, live in urban settings, and the number is expected to rise to 80% by 2050, according to the World Economic Forum.

The researchers developed a theoretical framework on how urban land modifies both air temperature and air humidity and showed that these two effects have equal weight in heat stress as measured by the wet-bulb temperature, in contrary to other heat indexes, which weigh temperature more heavily than humidity. Wet-bulb temperature combines dry air temperature with humidity to measure humid heat. The results of the study, the authors note, raise important questions.

"Green vegetation can lower air temperature via water evaporation, but it can also increase heat burden because of air humidity. The question then is to what extent this humidifying effect erases the cooling benefit arising from temperature reduction. We hope to answer this question in a follow-up study, where we are comparing observations of the wet-bulb temperature in urban greenspaces (with dense tree cover) and those in built-up neighborhoods," Lee says.

Zhang says she hopes the study can lead to further research on how cities can mitigate heat stress.

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Changes in vegetation shaped global temperatures over last 10,000 years

Follow the pollen. Records from past plant life tell the real story of global temperatures, according to research from a climate scientist at Washington University in St. Louis.

Warmer temperatures brought plants -- and then came even warmer temperatures, according to new model simulations published April 15 in Science Advances.

Alexander Thompson, a postdoctoral research associate in earth and planetary sciences in Arts & Sciences, updated simulations from an important climate model to reflect the role of changing vegetation as a key driver of global temperatures over the last 10,000 years.

Thompson had long been troubled by a problem with models of Earth's atmospheric temperatures since the last ice age. Too many of these simulations showed temperatures warming consistently over time.

But climate proxy records tell a different story. Many of those sources indicate a marked peak in global temperatures that occurred between 6,000 and 9,000 years ago.

Thompson had a hunch that the models could be overlooking the role of changes in vegetation in favor of impacts from atmospheric carbon dioxide concentrations or ice cover.

"Pollen records suggest a large expansion of vegetation during that time," Thompson said.

"But previous models only show a limited amount of vegetation growth," he said. "So, even though some of these other simulations have included dynamic vegetation, it wasn't nearly enough of a vegetation shift to account for what the pollen records suggest."

In reality, the changes to vegetative cover were significant.

Early in the Holocene, the current geological epoch, the Sahara Desert in Africa grew greener than today -- it was more of a grassland. Other Northern Hemisphere vegetation including the coniferous and deciduous forests in the mid-latitudes and the Arctic also thrived.

Thompson took evidence from pollen records and designed a set of experiments with a climate model known as the Community Earth System Model (CESM), one of the best-regarded models in a wide-ranging class of such models. He ran simulations to account for a range of changes in vegetation that had not been previously considered.

"Expanded vegetation during the Holocene warmed the globe by as much as 1.5 degrees Fahrenheit," Thompson said. "Our new simulations align closely with paleoclimate proxies. So this is exciting that we can point to Northern Hemisphere vegetation as one potential factor that allows us to resolve the controversial Holocene temperature conundrum."

Understanding the scale and timing of temperature change throughout the Holocene is important because it is a period of recent history, geologically speaking. The rise of human agriculture and civilization occurred during this time, so many scientists and historians from different disciplines are interested in understanding how early and mid-Holocene climate differed from the present day.

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Snow cover critical for revegetation following forest fires

With wildfires devastating mountain ecosystems across the western United States, their successful forest revegetation recovery hinges on, among other factors, an adequate lasting snowpack, according to research by the University of Nevada, Reno and Oregon State University.

"Our study illustrated that summer precipitation, snow cover and elevation were all important drivers of revegetation success," said Anne Nolin, a hydrologist and geography professor at the University of Nevada, Reno and formerly at Oregon State University. "In particular, we found that snow cover was a critical explanatory variable for revegetation in the Oregon and Washington Cascades. This could help inform revegetation management practices following severe wildfires."

Climate change has already increased the fraction of winter precipitation that falls as rain rather than snow, reduced the spring snow water equivalent -- a metric for how much water snow contains -- and caused snowmelt to begin earlier in the spring than it used to, Nolin explained. Pacific Northwest snowpacks have seen the greatest declines of any seasonal snow region in the West.

The research, led by Nolin, examined the 260,000-square-mile Columbia River Basin in the Pacific Northwest. She teamed with co-author Andrew Wilson, a graduate research assistant in OSU's College of Earth, Ocean, and Atmospheric Science, and co-author Kevin Bladon of OSU's College of Forestry for the study.

The NASA-supported study featured before-and-after vegetation analyses for two dozen high-severity wildfires. The fires occurred over a 10-year period among the four distinct subregions of the Columbia River Basin. There are many short- and long-term effects from these fires, including erosion, debris flows and water quality issues, which can affect the health of aquatic ecosystems and downstream community water supply, highlighting the importance of understanding post-fire forest rehabilitation.

In their paper published in the Journal of Geophysical Research -- Biogeosciences, "Assessing the Role of Snow Cover for Post-Wildfire Revegetation Across the Pacific Northwest," the findings show that given the trends of increasing wildfire activity, lower snowpacks, and earlier snow disappearance dates across the Pacific Northwest, forests will likely experience more frequent drought conditions, which will negatively impact the success of post?wildfire vegetation recovery with a number of impacts to the ecosystem.

"This knowledge may be used to facilitate adaptive post-fire management policies and decisions to ensure long-term forest health," Nolin, who is also director of the University of Nevada, Reno's Graduate Program of Hydrological Sciences, said. "For example, depending on the sub-region and species composition, reseeding efforts following low snow winters might employ more drought tolerant species or, replanting could be delayed one to two years until snowmelt and soil moisture conditions are more favorable for seedling propagation.

"However, climate change projections and shifting wildfire regimes have increased concerns about post-fire regeneration and, as such it is imperative that we broaden our understanding of the role of snowpacks in post-wildfire forest regeneration. The snowpacks' role in aiding revegetation will become increasingly important across the West. And where snowpacks have declined, there likely will be ecosystem transitions that look like a shift from forest to non-forest and from evergreen to deciduous vegetation."

Wildfires continue to burn more area each year across many regions of the planet, including the Pacific Northwest. The Pacific Northwest's largest watershed, the Columbia River Basin contains a variety of fire-prone landscapes that have seen almost 900 fires since 2010, serves as critical habitat for more than 700 species and is a water source for seven states.

"As wildfire activity continues to increase and intensify in the Northwest, understanding what shapes revegetation on severely burned forested landscapes is vital for guiding management decisions," co-author Bladon said.

After the occurrence of a wildfire, revegetation over the burned area is critical to maintain or re-establish ecosystem functions from forests such as biodiversity, erosion control, water purification and habitat provision.

"Snow matters to regrowing vegetation following fire, and with double impacts of declining snowpacks and increasing wildfires it is critical that we understand how these changes are affecting Pacific Northwest forests," Nolin said. "Positive relationships between snow cover and summer precipitation with post-fire greening suggest that active post-fire revegetation efforts will help facilitate recovery, especially during years when severe wildfires are followed by early snowmelt years or below average summer precipitation."

In the study, summer precipitation consistently appeared as the most important variable driving post-fire revegetation across all four subregions. Snow cover frequency, along with elevation, were shown to be secondary but significantly influential explanatory variables for revegetation in the Oregon and Washington Cascades.

More than 80% of wildfires in the western United States from 2000 to 2012 burned within a seasonal snow zone, a time period that overlaps with the years studied by the scientists.

"As wildfire activity continues to increase and intensify in the Northwest, understanding what shapes revegetation on severely burned forested landscapes is vital for guiding management decisions," Bladon said. "But variables such as snow cover frequency, pre-fire forest composition, and elevation, were also shown to be significantly influential for revegetation in the Oregon and Washington Cascades."

Wildfire season length in the western U.S. overall has increased by roughly 25 days in recent decades, including a massive increase in the Northwest from the mid-1970s, when it was 23 days, to 116 days in the early 2000s. That's attributable mainly to warmer temperatures and drier conditions in the spring and summer.

"Snow cover has a strong influence on postfire vegetation greening, but the influence varied depending on subregion and dominant prefire conifer species, with the biggest impacts at low to moderate elevations in the Washington Cascades, the Oregon Cascades and western Montana Rockies," Nolin said. "And with current climate change projections, snowpacks' role in aiding revegetation will become increasingly important across the West."

Bladon suggests fire can be looked at as an opportunity for forests to reassemble into ecosystems better suited to survive warmer winters, longer fire seasons and more drought stress.

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Bering Sea ice extent is at most reduced state in last 5,500 years

 Through the analysis of vegetation from a Bering Sea island, researchers have determined that the extent of sea ice in the region is lower than it's been for thousands of years.

A newly published paper in the journal Science Advances describes how a peat core from St. Matthew Island is providing a look back in time. By analyzing the chemical composition of the core, which includes plant remains from 5,500 years ago to the present, scientists can estimate how sea ice in the region has changed during that time period.

"It's a small island in the middle of the Bering Sea, and it's essentially been recording what's happening in the ocean and atmosphere around it," said lead author Miriam Jones, a research geologist with the U.S. Geological Survey. Jones worked as a faculty researcher at the University of Alaska Fairbanks when the project began in 2012.

The ancient sea ice record comes in the form of changes in the relative amounts of two isotopes of the element oxygen -- oxygen-16 and oxygen-18. The ratio of those two isotopes changes depending on patterns in the atmosphere and ocean, reflecting the different signatures that precipitation has around the globe. More oxygen-18 makes for an isotopically "heavier" precipitation, more oxygen-16 makes precipitation "lighter."

By analyzing data from a model that tracks atmospheric movement using the isotopic signature of precipitation, the authors found that heavier precipitation originated from the North Pacific, while lighter precipitation originated from the Arctic.

A "heavy" ratio signals a seasonal pattern that causes the amount of sea ice to decrease. A "light" ratio indicates a season with more sea ice. That connection has been confirmed though sea ice satellite data collected since 1979, and to a smaller extent, through the presence of some microorganisms in previous core samples.

UAF's Alaska Stable Isotope Facility analyzed isotope ratios throughout the peat layers, providing a time stamp for ice conditions that existed through the millennia.

After reviewing the isotopic history, researchers determined that modern ice conditions are at remarkably low levels.

"What we've seen most recently is unprecedented in the last 5,500 years," said Matthew Wooller, director of the Alaska Stable Isotope Facility and a contributor to the paper. "We haven't seen anything like this in terms of sea ice in the Bering Sea."

Jones said the long-term findings also affirm that reductions in Bering Sea ice are due to more than recent higher temperatures associated with global warming. Atmospheric and ocean currents, which are also affected by climate change, play a larger role in the presence of sea ice.

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