Scorching storms on distant worlds revealed

Astronomers have created the most detailed weather report so far for two distant worlds beyond our own solar system.

The international study -- the first of its kind -- reveals the extreme atmospheric conditions on the celestial objects, which are swathed in swirling clouds of hot sand amid temperatures of 950C.

Using NASA's powerful James Webb Space Telescope (JWST), researchers set out to capture the weather on a pair of brown dwarfs -- cosmic bodies that are bigger than planets but smaller than stars.

These brown dwarfs, named collectively as WISE 1049AB, are the brightest and closest objects of their type to Earth, around six light years away.

The team tracked each brown dwarf's atmosphere by measuring the light waves emitted from their surfaces, which change as more or less cloudy regions revolve in and out of view.

By visualising this data through light curves -- a plot of how the brightness of light from each object changes over time -- the team was able to build up a detailed 3D picture of how the brown dwarfs' weather changed over the course of a full rotation or day, between five and seven hours.

The team was also able to plot how the light from each object varied by wavelength, to demonstrate the presence and complex interplay of gases such as water, methane, and carbon monoxide in their atmospheres.

The insights may help astronomers develop the understanding of brown dwarfs as a potential missing link between stars and planets -- promising new insights into both.

By observing the infrared part of the light spectrum, the JWST is able to observe wavelengths of light that are blocked by our own atmosphere.

This capability opens frontiers in the study of the early universe, star formation, and so-called exoplanets such as brown dwarfs which lie beyond our solar system.

The latest study builds on previous studies of brown dwarfs, which have mainly been confined to capturing static snapshots of their atmosphere on only one side. This approach is limited, as brown dwarfs are known to rotate relatively quickly and their weather can vary greatly over time, researchers say.

Their findings will pave the way for more detailed studies into brown dwarfs and other distant celestial objects.

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NASA's Webb maps weather on planet 280 light-years away

An international team of researchers has successfully used NASA's James Webb Space Telescope to map the weather on the hot gas-giant exoplanet WASP-43 b.

Precise brightness measurements over a broad spectrum of mid-infrared light, combined with 3D climate models and previous observations from other telescopes, suggest the presence of thick, high clouds covering the nightside, clear skies on the dayside, and equatorial winds upwards of 5,000 miles per hour mixing atmospheric gases around the planet.

The investigation is just the latest demonstration of the exoplanet science now possible with Webb's extraordinary ability to measure temperature variations and detect atmospheric gases trillions of miles away.

Tidally Locked "Hot Jupiter"

WASP-43 b is a "hot Jupiter" type of exoplanet: similar in size to Jupiter, made primarily of hydrogen and helium, and much hotter than any of the giant planets in our own solar system. Although its star is smaller and cooler than the Sun, WASP-43 b orbits at a distance of just 1.3 million miles -- less than 1/25th the distance between Mercury and the Sun.

With such a tight orbit, the planet is tidally locked, with one side continuously illuminated and the other in permanent darkness. Although the nightside never receives any direct radiation from the star, strong eastward winds transport heat around from the dayside.

Since its discovery in 2011, WASP-43 b has been observed with numerous telescopes, including NASA's Hubble and now-retired Spitzer space telescopes.

"With Hubble, we could clearly see that there is water vapor on the dayside. Both Hubble and Spitzer suggested there might be clouds on the nightside," explained Taylor Bell, researcher from the Bay Area Environmental Research Institute and lead author of a study published today in Nature Astronomy. "But we needed more precise measurements from Webb to really begin mapping the temperature, cloud cover, winds, and more detailed atmospheric composition all the way around the planet."

Mapping Temperature and Inferring Weather

Although WASP-43 b is too small, dim, and close to its star for a telescope to see directly, its short orbital period of just 19.5 hours makes it ideal for phase curve spectroscopy, a technique that involves measuring tiny changes in brightness of the star-planet system as the planet orbits the star.

Since the amount of mid-infrared light given off by an object depends largely on how hot it is, the brightness data captured by Webb can then be used to calculate the planet's temperature.

The team used Webb's MIRI (Mid-Infrared Instrument) to measure light from the WASP-43 system every 10 seconds for more than 24 hours. "By observing over an entire orbit, we were able to calculate the temperature of different sides of the planet as they rotate into view," explained Bell. "From that, we could construct a rough map of temperature across the planet."

The measurements show that the dayside has an average temperature of nearly 2,300 degrees Fahrenheit (1,250 degrees Celsius) -- hot enough to forge iron. Meanwhile, the nightside is significantly cooler at 1,100 degrees Fahrenheit (600 degrees Celsius). The data also helps locate the hottest spot on the planet (the "hotspot"), which is shifted slightly eastward from the point that receives the most stellar radiation, where the star is highest in the planet's sky. This shift occurs because of supersonic winds, which move heated air eastward.

"The fact that we can map temperature in this way is a real testament to Webb's sensitivity and stability," said Michael Roman, a co-author from the University of Leicester in the U.K.

To interpret the map, the team used complex 3D atmospheric models like those used to understand weather and climate on Earth. The analysis shows that the nightside is probably covered in a thick, high layer of clouds that prevent some of the infrared light from escaping to space. As a result, the nightside -- while very hot -- looks dimmer and cooler than it would if there were no clouds.

Missing Methane and High Winds

The broad spectrum of mid-infrared light captured by Webb also made it possible to measure the amount of water vapor (H2O) and methane (CH4) around the planet. "Webb has given us an opportunity to figure out exactly which molecules we're seeing and put some limits on the abundances," said Joanna Barstow, a co-author from the Open University in the U.K.

The spectra show clear signs of water vapor on the nightside as well as the dayside of the planet, providing additional information about how thick the clouds are and how high they extend in the atmosphere.

Surprisingly, the data also shows a distinct lack of methane anywhere in the atmosphere. Although the dayside is too hot for methane to exist (most of the carbon should be in the form of carbon monoxide), methane should be stable and detectable on the cooler nightside.

"The fact that we don't see methane tells us that WASP-43b must have wind speeds reaching something like 5,000 miles per hour," explained Barstow. "If winds move gas around from the dayside to the nightside and back again fast enough, there isn't enough time for the expected chemical reactions to produce detectable amounts of methane on the nightside."

The team thinks that because of this wind-driven mixing, the atmospheric chemistry is the same all the way around the planet, which wasn't apparent from past work with Hubble and Spitzer.

Read more at Science Daily

Scientists capture X-rays from upward positive lightning

Globally, lightning is responsible for over 4,000 fatalities and billions of dollars in damage every year; Switzerland itself weathers up to 150,000 strikes annually. Understanding exactly how lightning forms is key for reducing risk, but because lightning phenomena occur on sub-millisecond timescales, direct measurements are extremely difficult to obtain.

Now, researchers from the Electromagnetic Compatibility Lab, led by Farhad Rachidi, in EPFL's School of Engineering have for the first time directly measured an elusive phenomenon that explains a lot about the birth of a lightning bolt: X-ray radiation. In a collaborative study with the University of Applied Sciences of Western Switzerland and Uppsala University in Sweden, they recorded lightning strikes at the Säntis tower in northeastern Switzerland, identifying X-rays associated with the beginning of upward positive flashes. These flashes start with negatively charged tendrils (leaders) that ascend stepwise from a high-altitude object, before connecting with a thundercloud, transferring positive charge to the ground.

"At sea level, upward flashes are rare, but could become the dominant type at high altitudes. They also have the potential to be more damaging, because in an upward flash, lightning remains in contact with a structure for longer than it does during a downward flash, giving it more time to transfer electrical charge," explains Electromagnetic Compatibility Lab PhD candidate Toma Oregel-Chaumont.

Although X-ray emissions have previously been observed from other types of lightning, this is the first time they have been captured from upward positive flashes. Oregel-Chaumont, the first author on a recent Nature Scientific Reports paper describing the observations, says that they offer valuable insights into how lightning -- and upward lightning in particular -- forms.

"The actual mechanism by which lightning initiates and propagates is still a mystery. The observation of upward lightning from tall structures like the Säntis tower makes it possible to correlate X-ray measurements with other simultaneously measured quantities, like high-speed video observations and electric currents."

A unique observation opportunity

It's perhaps not surprising that the novel observations were made in Switzerland, as the Säntis tower offers unique and ideal measurement conditions. The 124-meter tower is perched atop a high peak of the Appenzell Alps, making it a prime lightning target. There is a clear line of sight from neighboring peaks, and the expansive research facility is packed with

high-speed cameras, X-ray detectors, electric field sensors, and current-measuring devices.

Crucially, the speed and sensitivity of this equipment allowed the team to see a difference between negative leader steps that emitted X-rays and those that did not, supporting a theory of lightning formation known as the cold runaway electron model. In a nutshell, the association of X-rays with very rapid electric field changes supported the theory that sudden increases in the air's electric field causes ambient electrons to "run away" and become a plasma: lightning.

"As a physicist, I like to be able to understand the theory behind observations, but this information is also important for understanding lightning from an engineering perspective: More and more high-altitude structures, like wind turbines and aircraft, are being built from composite materials. These are less conductive than metals like aluminum, so they heat up more, making them vulnerable to damage from upward lightning," Oregel-Chaumont says.

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Meteorology: Weak polar vortex makes weather more predictable

Events in the stratosphere are making long-range weather in Northern Europe easier to forecast, researchers at LMU have discovered.

Weather is a chaotic system and predicting weather conditions several weeks in advance poses considerable challenges.

The accuracy of such long-range forecasts remains generally quite low.

Accordingly, even moderate improvements can prove valuable for various sectors.

For instance, farmers rely on these forecasts to determine optimal sowing and harvesting times, energy providers use them to anticipate fluctuations in renewable energy production, and public health officials use them to prepare for outbreaks of diseases such as malaria or dengue fever, which are correlated with specific weather conditions.

Researchers at LMU are now investigating a phenomenon that has its origin in the stratosphere, the layer of our atmosphere situated 15 to 50 kilometers above our heads.

"Previous work has shown that during Northern winter the state of the circulation in the polar stratosphere may provide useful information for improved long-range forecasts, especially for weather over the North Atlantic and Eurasia," explains Thomas Birner, Professor of Theoretical Meteorology at LMU.

In particular, when the polar vortex (a band of strong eastward circumpolar flow at stratospheric levels) strongly weakens or breaks down, the North Atlantic jetstream tends to shift southward and the likelihood of cold spells over Eurasia increases.

Such vortex breakdowns are relatively rare events that only happen approximately every other winter.

But its time has come round again: "One such event is currently unfolding with corresponding expected impacts on Eurasian weather in the coming weeks."

And now for the weather: cold, but less chaotic

In a study published recently in the journal Communications Earth & Environment, LMU meteorologists highlight an additional aspect of stratospheric influence on long-range weather forecasts: Weak polar vortex states, such as the one currently prevailing, are typically followed by reduced uncertainty of 3-5 week forecasts over Northern Europe.

The authors found that ensembles of forecasts show a reduced range of possible weather conditions by about 25%. Such ensembles are made up of a large number of individual forecasts, which typically diverge at longer forecasting periods.

After weak polar vortex events there is less spread among these forecasts over Northern Europe, making the weather more predictable.

"We attribute this reduced forecast uncertainty to the southward shift of the North Atlantic jetstream," says Jonas Spaeth, doctoral student at LMU's Meteorological Institute and lead author of the new study.

The associated southward shift of the tracks of winter storms, which are the main source of forecast uncertainty during this season, causes less storm activity and thereby reduced forecast uncertainty over Northern Europe.

Conversely, forecast uncertainty increases over Southern Europe.

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Butterflies could lose spots as climate warms

Female Meadow Brown butterflies have fewer spots if they develop in warmer weather -- so climate change could make them less spotty, new research shows.

University of Exeter scientists found females that developed at 11°C had six spots on average, while those developing 15°C had just three.

The findings challenge long-held scientific views about why these butterflies have varying numbers of spots.

"Meadow Browns always have large 'eyespots' on their forewings, probably for startling predators," said Professor Richard ffrench-Constant, from the Centre for Ecology and Conservation on Exeter's Penryn Campus in Cornwall.

"They also have smaller spots on their hindwings, probably useful for camouflage when the butterfly is at rest.

"Our findings show that fewer of these hindwing spots appear when females experience higher temperatures during their pupal stage (in a chrysalis before emerging as a butterfly).

"This suggests the butterflies adapt their camouflage based on the conditions. For example, with fewer spots they may be harder to spot on dry, brown grass that would be more common in hot weather.

"We did not observe such a strong effect in males, possibly because their spots are important for sexual selection (attracting females)."

Since the classic work of biologist EB Ford, eyespot variation in the Meadow Brown butterfly has been used as an example of "genetic polymorphism" (the co-existence of multiple genetic forms in a single population).

However, the new study shows the eyespot variation is caused by thermal plasticity (the ability to react to changing temperatures).

"This is a family story for me, as my father collected butterflies for EB Ford here in Cornwall," Professor ffrench-Constant said.

"In the new study, we looked at current Cornish populations -- collecting males and females from the same field every day throughout the flight season -- and historical collections from Eton and Buckingham."

The researchers predict that spotting will decrease year on year as our climate warms.

Professor ffrench-Constant added: "This is an unexpected consequence of climate change. We tend to think about species moving north, rather than changing appearance."

Read more at Science Daily

Not so silver lining: Microplastics found in clouds could affect the weather

From the depths of the seas to snow on mountains and even the air above cities, microplastics are turning up increasingly often. Now, in ACS' Environmental Science & Technology Letters, researchers have analyzed microplastics in clouds above mountains. They suggest that these tiny particles could play a role in cloud formation and, in turn, affect weather.

Microplastics -- plastic fragments smaller than five millimeters -- originate from a myriad of items used daily, such as clothing, packaging and car tires. As research in the field evolves, scientists are not only detecting microplastics in the atmosphere but also investigating how they may play a role in cloud formation. For example, a group of researchers recently detected plastic granules, which had water-attracting surfaces, in Japanese mountaintop clouds. So, to learn more, Yan Wang and colleagues set out to look for microplastics in mountain clouds, used computer models to figure out how they could have gotten there, and tested how the particles could have impacted -- and been impacted by -- the clouds.

Wang and the team first collected 28 samples of liquid from clouds at the top of Mount Tai in eastern China. Then they analyzed the samples and found:

• Low-altitude and denser clouds contained greater amounts of microplastics.
• Particles were made of common polymers, including polyethylene terephthalate, polypropylene, polyethylene, polystyrene and polyamide.
• The microplastics tended to be smaller than 100 micrometers in length, although some were as long as 1,500 micrometers.
• Older, rougher particles had more lead, mercury and oxygen attached to their surfaces, which the researchers suggest could facilitate cloud development.

To investigate where the plastic particles in the clouds originated, Wang and the team developed computer models that approximated how the particles traveled to Mount Tai. These models suggested that airflow from highly populated inland areas, rather than from over the ocean or other nearby mountains, served as the major source of the fragments. In laboratory experiments, the researchers demonstrated that microplastics exposed to cloud-like conditions -- ultraviolet light and filtered cloud-sourced water -- had smaller sizes and rougher surfaces than those exposed to pure water or air. Additionally, particles impacted by the cloud-like conditions had more lead, mercury and oxygen-containing groups. These results suggest that clouds modify microplastics in ways that could enable the particles to affect cloud formation and the fate of airborne metals. The researchers conclude that more work is needed to fully understand how microplastics affect clouds and the weather.

Read more at Science Daily

Rider on the storm: Shearwater seabird catches an 11 hour ride over 1,000 miles in a typhoon

New research from Japan published in the Ecological Society of America's journal Ecology suggests that increasingly severe weather driven by climate change may push oceangoing seabirds to their limits.

In August 2019, Kozue Shiomi, a seabird biologist at Tohoku University, attached GPS bio-loggers to 14 adult streaked shearwaters (Calonectris leucomelas) from a nesting colony on Mikurajima, a small island near Tokyo, as part of a study on the species homing behavior.

In September of that same year, an exceptionally powerful storm, Typhoon Faxai, barreled into southeastern Japan, causing considerable physical damage to the mainland. But the typhoon, with windspeeds nearing 200 km/hr, also provided scientists with a rare glimpse into the capacity of seabirds to withstand extreme storm conditions -- conditions that seabirds may increasingly be faced with under future climates.

Analysis of tracking data following the passage of Typhoon Faxai revealed that, while most of the tagged shearwaters appeared to be either unaffected by or had managed to circumvent the storm, one male had not been so lucky. Over the 11-hour period during which this shearwater bird was tracked, it completed five full circular loops of 50-80 km diameter each and was transported a total distance of 1,146 km.

Under normal conditions, streaked shearwaters typically fly at speeds of 10-60 km/hr and altitudes below 100 m, and remain at sea; by contrast, tracking data indicated that the bird caught in the storm had attained speeds of 90-170 km/hr, soared to an altitude of 4700 m, and was carried over mainland Japan before the typhoon swung back into the Pacific Ocean.

Although it cannot be known for certain, it is possible that the shearwater was capable of escaping from the typhoon but instead chose to ride it out until the storm moved back over the ocean. Like most birds adapted to a life at sea, streaked shearwaters typically fly at very low altitudes, an efficient flight strategy over the open ocean that also puts them at higher risk of collisions with buildings, power lines and vehicles when over land. Moreover, they are clumsy on solid ground, and if forced to land have difficulty taking off, rendering them highly vulnerable to predation.

Pelagic birds resort to a wide range of tactics to avoid being caught within the tumult of large storms. Red-footed boobies and great frigatebirds, for instance, often take to the wing and ascend to high altitudes, allowing storms to pass below, whereas Eastern brown pelicans simply sit them out, remaining grounded until conditions improve. Still others elect to stay within the eye of the storm, where winds are calmer.

Read more at Science Daily

Three things to know: Climate change's impact on extreme-weather events

In an article published in the Proceedings of the National Academy of Sciences, Michael Mann, professor in the Department of Earth and Environmental Science in the University of Pennsylvania's School of Arts & Sciences, and colleagues from Clemson University, the University of California Los Angeles, and Columbia University investigate the effects of climate change on exacerbating compounding heat and drought situations.

Their findings offer new insights into predicting their interplay, which will provide scientists and policymakers with a clearer and more holistic approach to preventing and preparing for extreme-weather events.

"We wanted to see how the state-of-the-art climate models used in the most recent assessment reports of the Intergovernmental Panel on Climate Change address the episodes of heat waves and droughts that have given rise to some of the worst wildfires we've witnessed in recent history," Mann says.

"We also wanted to get a better understanding of how often these events were occurring, their typical durations, and their intensity to improve not only our forecasting but approaches to mitigating further damage to human life."

Compound drought and heat wave events and their effects

The researchers document the deleterious effects of increasingly severe droughts and wildfires occurring in the past three years.

"Two standout events," Mann says, "were the 2020 California wildfires and the 2019-20 Australian bush fire season, which lasted nearly one whole year and came to be known as the Black Summer. These are known as compound drought and heat wave (CDHW) events and refer to situations wherein a region experiences both prolonged hot temperatures and a shortage of water."

These conditions can occur together and worsen each other's impacts, the researchers say, and could potentially lead to heat-related illnesses and deaths, water scarcity for drinking and agriculture, reduced crop yields, increased wildfire risk, and ecological stress. They also note that anthropogenic climate change -- climate change that is driven by human activity -- can contribute to the frequency and severity of these events.

Projected impact of a worst-case versus moderate-case scenario

The researchers compared two contrasting socioeconomic pathways: the high-end or worst-case scenario, wherein society fails to mitigate the effects of anthropogenic climate change, and a moderate scenario, wherein some conservative measures are put in place and efforts are made to abide by them.

In the worst-case scenario, they found that by the late 21st century approximately 20% of global land areas are expected to witness approximately two CDHW events per year. These events could last for around 25 days and a fourfold increase in severity.

"Comparatively, the average CDHW frequency over the recent observed reference period was approximately 1.2 events per year, lasting less than 10 days, with far less severity," Mann says.

The most vulnerable geographical regions, such as eastern North America, southeastern South America, Central Europe, East Africa, Central Asia, and northern Australia, are projected to experience the largest increases in CDHW frequency by the end of the 21st century.

"Interestingly, places like Philadelphia and some of the regions in the eastern U.S. are where we expect to see an increase in these sorts of events; urban environments in the summertime will witness the highest relative frequency of these events," Mann says.

Critical need for proactive measures

The researchers emphasize the profound threat posed by more frequent and intense CDHW events in the coming decades and the dependence the emissions pathway chosen has on the severity of these events.

As climate change continues to unfold, addressing the escalating risks associated with CDHW events becomes crucial. This study contributes to the growing understanding of the projected changes in CDHWs and highlights the need for proactive measures, including emission reductions and adaptation strategies, to build resilience and safeguard vulnerable regions from the impacts of compound drought and heat wave events.

"Our findings provide important scientific context for the record heat and wildfire that we're witnessing right now here in the United States," Mann says.

"They underscore that we need to get off fossil fuels as quickly as possible to prevent a worsening of these dangerous combinations of heat and drought."

Read more at Science Daily

120-year-old storm's secrets key to understanding weather risks

A severe windstorm that battered the UK more than a century ago produced some of the strongest winds[OS1] that Britain has ever seen, a team of scientists have found after recovering old weather records.

Old weather measurements, first recorded on paper after Storm Ulysses hit the UK in February 1903, have shed new light on what was one of the most severe storms to have hit the British Isles.

By turning hand-written weather data into digital records, the research team has laid the way to better understand other historical storms, floods and heatwaves. These observations from the past can help experts to understand the risks of extreme weather now and in the future.

Professor Ed Hawkins, a climate scientist at the University of Reading and the National Centre for Atmospheric Science, led the research. He said: "We knew the storm we analysed was a big one, but we didn't know our rescued data would show that it is among the top four storms for strongest winds across England and Wales.

"This study is a great example of how rescuing old paper records can help us to better understand storms from decades gone by. Unlocking these secrets from the past could transform our understanding of extreme weather and the risks they pose to us today."

Into the archives

Published today (Monday, 24 April) in Natural Hazards and Earth System Sciences, the research indicates that many storms that occurred before 1950 are left unstudied as billions of pieces of data exist only on paper, stored in archives around the world.

But a team of scientists led by Professor Hawkins delved into the archives to convert hand-written observations relating to Storm Ulysses from paper to digital. The cyclone caused multiple deaths and heavily damaged infrastructure and ships when it passed across Ireland and the UK between 26 and 27 February 1903.

Using the new digital data, the research team was able to use techniques similar to modern weather forecasting to simulate the storm and accurately assess the strength of Storm Ulysses' winds. Comparisons with independent weather observations, such as rainfall data, as well as photographs and written accounts from 1903 that outlined the devastation caused by the cyclone, helped to provide credibility for the reconstruction.

The reanalysis is beneficial for understanding the risks of extreme weather events as it showed that the winds experienced in some locations during Storm Ulysses would be rarer than once in 100 years. Having information about such a rare event provides valuable insight into the potential damage a similar storm could cause now in the future.

The 1903 storm is named Storm Ulysses because the damage to thousands of trees in Dublin is mentioned in the novel Ulysses by James Joyce, the events of which are set the year after the storm.

Rescuing the weather

The rescuing of atmospheric observations related to Storm Ulysses is not the first time Professor Ed Hawkins has led weather record recovery. National rainfall data from as far back as 1836 became available in 2022 after the University's Department of Meteorology and 16,000 volunteers helped to restore 5.2 million observations.

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Researchers correlate Arctic warming to extreme winter weather in midlatitude and its future

A warmer Arctic has been linked to extreme winter weather in the midlatitude regions. But, it is not clear how global warming affects this link. In a new study, researchers from Korea and USA show, using weather data and climate models, that while the "Warm Arctic-Cold Continent" pattern will continue as the climate continues to warm, Arctic warming will become a less reliable predictor of extreme winter weather in the future.

Pictures of melting glaciers and stranded polar bears on shrinking sea ice in the Arctic are perhaps the most striking images that have been used to highlights the effects of global warming. However, they do not convey the full extent of the consequences of warmer Arctic. In recent years, there has been growing recognition of the Arctic's role in driving extreme weather events in other parts of the world. While the Arctic has been warming at a rate twice as fast as the global average, winters in the midlatitude regions have experienced colder and more severe weather events. For instance, the winter of 2022-2023 saw record-breaking cold temperatures and snowfall in Japan, China, and Korea. Similarly, many parts of Eurasia and North America have experienced severe cold snaps, with heavy snowfall and prolonged periods of sub-zero temperatures.

While there are multiple theories for this climate phenomenon, an international team of researchers led by Professor Jin-Ho Yoon from Gwangju Institute of Science and Technology (GIST), Korea set out to examine the relationship between the severe winters in the Northern Hemisphere and the melting sea ice in the Arctic region, a phenomenon referred to as the "Warm Arctic-Cold Continent" (WACC), and how this relationship changed with the warming climate.

In their study published online on 27 March 2023 in the journal npj Climate and Atmospheric Science, the researchers looked at historic climate data and turned to climate projection models to explore the potential connection and assess how this phenomenon might be influenced by different global warming scenarios.

Based on the climate data from the European Center for Medium-Range Weather Forecasting (ECMWF) going back almost 40 years, the researchers correlated winter temperatures in East Asia and North America to the temperatures of the Barents-Kara Sea and the East Siberian-Chukchi Sea in the Arctic region. They observed that lower winter temperatures in East Asia and North America are usually accompanied by warmer Arctic Sea temperatures. However, they also found that in some winters, such as the 2017/18 winter in East Asia, this pattern did not hold, suggesting that this linkage include uncertainty likely due to factors other than Arctic Sea temperatures were at play.

Nonetheless, using climate projections from the Half degree Additional warming, Prognosis and Projected Impacts (HAPPI) experiments which were targeted to project future climate under 1.5°C to 2°C warming scenarios, the researchers found the WACC pattern to persist even when global temperatures rose. However, they found that the correlation between the Arctic Sea temperature and the East Asia temperatures became more uncertain with the intensification of global warming. "We found that the relationship between Arctic warming and cold weather events in midlatitude would become more uncertain under warmer climates, challenging the forecast of winter temperature in the future," says Mr. Yungi Hong, a Ph.D. student at GIST and a member of the research team.

"Our study shows that while one can expect the Arctic warming-triggered cold waves in the midlatitudes to persist in a warmer future, they will become more difficult to predict," adds Prof. Jin-Ho Yoon.

Read more at Science Daily

Monitoring an 'anti-greenhouse' gas: Dimethyl sulfide in Arctic air

Data stored in ice cores dating back 55 years bring new insight into atmospheric levels of a molecule that can significantly affect weather and climate.

Dimethyl sulfide (C2H6S) is a small molecule released by phytoplankton in the ocean, which can play a big role in regulating the Earth's climate. It encourages cloud formation above the sea, and is often called an 'anti-greenhouse gas', since clouds block radiation from the sun and lower sea surface temperatures. At least some blocked heat will be retained in the atmosphere, however, so the effects can be complex. Researchers at Hokkaido University have charted evidence for increasing dimethyl sulfide emissions linked to the retreat of sea ice from Greenland as the planet warms. They report their findings in the journal Communications Earth & Environment.

Modelling studies have long suggested that the decline in Arctic sea ice could lead to increased dimethyl sulfide emission, but direct evidence for this has been lacking. Assistant Professor Sumito Matoba and colleagues have inferred dimethyl sulfide levels over 55 years by quantifying the related compound, methane sulfonic acid (MSA), in ice core samples from the south-east Greenland ice sheet. MSA is directly produced from dimethyl sulfide, serving as a stable record of dimethyl sulfide levels. This process is part of a variety of chemical interactions among aerosols in the atmosphere.

The team, including researchers from Nagoya University and Japan's Aerospace Exploration Agency, reconstructed the annual and seasonal MSA flux from 1960 to 2014, at a monthly resolution. The annual MSA levels decreased from 1960 to 2001, but then markedly increased after 2002.

"We found that July to September MSA fluxes were three to six times higher between 2002 and 2014 than between 1972 and 2001," says Matoba. "We attribute this to the earlier retreat of sea ice in recent years."

Supporting evidence comes from satellite data that has monitored the levels of the crucial sunlight-absorbing green pigment chlorophyll-a in the surrounding seas. The chlorophyll-a serves as an indicator of phytoplankton abundance, which in turn should correlate well with the amount of dimethyl sulfide released by the phytoplankton.

Arctic temperatures are rising twice as fast as the global average, and the summer seasonal sea ice extent has declined sharply in recent decades. This increases the amount of light striking the ocean and promotes the growth of phytoplankton.

Read more at Science Daily

17-pound meteorite discovered in Antarctica

Antarctica is a tough place to work, for obvious reasons -- it's bitterly cold, remote, and wild. However, it's one of the best places in the world to hunt for meteorites. That's partly because Antarctica is a desert, and its dry climate limits the degree of weathering the meteorites experience. On top of the dry conditions, the landscape is ideal for meteorite hunting: the black space rocks stand out clearly against snowy fields. Even when meteorites sink into the ice, the glaciers' churning motion against the rock below helps re-expose the meteorites near the surface of the continent's blue ice fields.

An international team of researchers who just got back from Antarctica can attest to the continent's meteorite-hunter-friendliness: they returned with five new meteorites, including one that weighs 16.7 pounds (7.6 kg).

Maria Valdes, a research scientist at the Field Museum and the University of Chicago, estimates that of the roughly 45,000 meteorites retrieved from Antarctica over the past century, only about a hundred or so are this size or larger. "Size doesn't necessarily matter when it comes to meteorites, and even tiny micrometeorites can be incredibly scientifically valuable," says Valdes, "but of course, finding a big meteorite like this one is rare, and really exciting."

Valdes was one of four scientists on the mission, led by Vinciane Debaille of the Université Libre de Bruxelles (FNRS-ULB); the research team was rounded out by Maria Schönbächler (ETH-Zurich) and Ryoga Maeda (VUB-ULB). The researchers were the first to explore potential new meteorite sites mapped using satellite imagery by Veronica Tollenaar, a thesis student in glaciology at the ULB.

"Going on an adventure exploring unknown areas is exciting," says Debaille, "but we also had to deal with the fact that the reality on the ground is much more difficult than the beauty of satellite images." Despite timing their trip for Antarctica's summertime in late December, temperatures hovered around 14° F (-10° C). Valdes notes that some days during their trip, it was actually colder in Chicago than it was in Antarctica, but spending days riding snowmobiles and trekking through ice fields and then sleeping in a tent made the Antarctic weather feel more extreme.

The five meteorites recovered by the team will be analyzed at the Royal Belgian Institute of Natural Sciences; meanwhile, sediment potentially containing tiny micrometeorites was divided among the researchers for study at their institutions.

Valdes says she's eager to see what the analyses of the meteorites reveal, because "studying meteorites helps us better understand our place in the universe. The bigger a sample size we have of meteorites, the better we can understand our Solar System, and the better we can understand ourselves."

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Earth-sun distance dramatically alters seasons in the equatorial Pacific in a 22,000-year cycle

Weather and climate modelers understand pretty well how seasonal winds and ocean currents affect El Niño patterns in the eastern equatorial Pacific Ocean, impacting weather across the United States and sometimes worldwide.

But new computer simulations show that one driver of annual weather cycles in that region -- in particular, a cold tongue of surface waters stretching westward along the equator from the coast of South America -- has gone unrecognized: the changing distance between Earth and the sun.

The cold tongue, in turn, influences the El Niño-Southern Oscillation (ENSO), which impacts weather in California, much of North America, and often globally.

The Earth-sun distance slowly varies over the course of the year because Earth's orbit is slightly elliptical. Currently, at its closest approach -- perihelion -- Earth is about 3 million miles closer to the sun than at its farthest point, or aphelion. As a result, sunlight is about 7% more intense at perihelion than at aphelion.

Research led by the University of California, Berkeley, demonstrates that the slight yearly change in our distance from the sun can have a large effect on the annual cycle of the cold tongue. This is distinct from the effect of Earth's axial tilt on the seasons, which is currently understood to cause the annual cycle of the cold tongue.

Because the period of the annual cycle arising from the tilt and distance effects are slightly different, their combined effects vary over time, said lead researcher John Chiang, UC Berkeley professor of geography.

"The curious thing is that the annual cycle from the distance effect is slightly longer than that for tilt -- around 25 minutes, currently -- so over a span of about 11,000 years, the two annual cycles go from being in phase to out of phase, and the net seasonality undergoes a remarkable change, as a result," Chiang said.

Chiang noted that the distance effect is already incorporated into climate models -- though its effect on the equatorial Pacific was not recognized until now -- and his findings will not alter weather predictions or climate projections. But the 22,000-year phase cycle may have had long-term, historical effects. Earth's orbital precession is known to have affected the timing of the ice ages, for example.

The distance effect -- and its 22,000-year variation -- also may affect other weather systems on Earth. The ENSO, which also originates in the equatorial Pacific, is likely affected because its workings are closely tied to the seasonal cycle of the cold tongue.

"Theory tells us that the seasonal cycle of the cold tongue plays a key role in the development and termination of ENSO events," said Alyssa Atwood, a former UC Berkeley postdoctoral fellow who is now an assistant professor at Florida State University in Tallahassee. "Because of this, many of ENSO's key characteristics are synced to the seasonal cycle."

For example, ENSO events tend to peak during Northern Hemisphere winters, she said, and they don't typically persist beyond northern or boreal spring months, which scientists refer to as the "spring predictability barrier." Because of these linkages, it is reasonable to expect that the distance effect could also have a major impact on ENSO -- something that should be examined in future studies.

"Very little attention has been paid to the cold tongue seasonal cycle because most people think it's solved. There's nothing interesting there," Chiang said. "What this research shows is that it's not solved. There's still a mystery there. Our result also begs the question whether other regions on Earth may also have a significant distance effect contribution to their seasonal cycle."

"We learn in science classes as early as grade school that the seasons are caused by the tilt of Earth's axis," added co-author Anthony Broccoli of Rutgers University. "This is certainly true and has been well understood for centuries. Although the effect of the Earth-sun distance has also been recognized, our study indicates that this 'distance effect' may be a more important effect on climate than had been recognized previously."

Chiang, Atwood and Broccoli and their colleagues reported their findings today in the journal Nature.

Two distinct yearly cycles affect Pacific cold tongue

The main driver of global weather changes is seasonal change. Earth's equator is tilted relative to its orbit around the sun, so the Northern and Southern hemispheres are illuminated differently. When the sun shines directly overhead in the north, it's warmer in the north and colder in the south, and vice versa.

These yearly changes have major effects on the Pacific equatorial trade winds, which blow from southeast to northwest across the south and equatorial Pacific and push surface waters westward, causing upwelling of cold water along the equator that creates a tongue of cold surface water that stretches from Ecuador across the Pacific -- almost one-quarter the circumference of the planet.

The yearly hemispheric changes in seasonal temperature alters the strength of the trades, and thus cause a yearly cycle in the temperature of the cold tongue. This, in turn, has a major influence on ENSO, which typically peaks during Northern Hemisphere winter.

The occurrence of El Niño -- or its opposite, La Niña -- helps determines whether California and the West Coast will have a wet or dry winter, but also whether the Midwest and parts of Asia will have rain or drought.

"In studying past climates, much effort has been dedicated to trying to understand if variability in the tropical Pacific Ocean -- that is, the El Niño/La Niña cycle -- has changed in the past," Broccoli said. "We chose to focus instead on the yearly cycle of ocean temperatures in the eastern Pacific cold tongue. Our study found that the timing of perihelion -- that is, the point at which the earth is closest to the sun -- has an important influence on climate in the tropical Pacific."

In 2015, Broccoli, co-director of the Rutgers Climate Institute, along with his then-graduate student Michael Erb, employed a computer climate model to show that the distance changes caused by Earth's elliptical orbit dramatically altered the cold tongue yearly cycle. But climate modelers mostly ignored the result, Chiang said.

"Our field is focused on El Niño, and we thought that the seasonal cycle was solved. But then we realized that the result by Erb and Broccoli challenged this assumption," he said.

Chiang and his colleagues, including Broccoli and Atwood, examined similar simulations using four different climate models and confirmed the result. But the team went further to show how the distance effect works.

Earth's 'marine' and 'continental' hemispheres

The key distinction is that changes in the sun's distance from Earth don't affect the Northern and Southern hemispheres differently, which is what gives rise to the seasonal effect due to Earth's axial tilt. Instead, they warm the eastern "continental hemisphere" dominated by the North and South American and African and Eurasian landmasses, more than it warms the Western Hemisphere -- what he calls the marine hemisphere, because it is dominated by the Pacific Ocean.

"The traditional way of thinking about monsoons is that the Northern Hemisphere warms up relative to the Southern Hemisphere, generating winds onto land that bring monsoon rains," Chiang said. "But here, we're actually talking about east-west, not north-south, temperature differences that cause the winds. The distance effect is operating through the same mechanism as the seasonal monsoon rains, but the wind changes are coming from this east-west monsoon."

The winds generated by this differential heating of the marine and continental hemispheres alter the yearly variation of the easterly trades in the western equatorial Pacific, and thereby the cold tongue.

"When Earth is closest to the sun, these winds are strong. In the offseason, when the sun is at its furthest, these winds become weak," Chiang said. "Those wind changes are then propagated to the Eastern Pacific through the thermocline, and basically it drives an annual cycle of the cold tongue, as a result."

Today, Chiang said, the distance effect on the cold tongue is about one-third the strength of the tilt effect, and they enhance one another, leading to a strong annual cycle of the cold tongue. About 6,000 years ago, they canceled one another, yielding a muted annual cycle of the cold tongue. In the past, when Earth's orbit was more elliptical, the distance effect on the cold tongue would have been larger and could have led to a more complete cancellation when out of phase.

Though Chiang and his colleagues did not examine the effect of such a cancellation, this would potentially have had a worldwide effect on weather patterns.

Chiang emphasized that the distance effect on climate, while clear in climate model simulations, would not be evident from observations because it cannot be readily distinguished from the tilt effect.

"This study is purely model based. So, it is a prediction," he said. "But this behavior is reproduced by a number of different models, at least four. And what we did in this study is to explain why this happens. And in the process, we've discovered another annual cycle of the cold tongue that's driven by Earth's eccentricity."

Atwood noted that, unlike the robust changes to the cold tongue seasonal cycle, changes to ENSO tend to be model-dependent.

"While ENSO remains a challenge for climate models, we can look beyond climate model simulations to the paleoclimate record to investigate the connection between changes in the annual cycle of the cold tongue and ENSO in the past," she said. "To date, paleoclimate records from the tropical Pacific have largely been interpreted in terms of past changes in ENSO, but our study underscores the need to separate changes in the cold tongue annual cycle from changes in ENSO."

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Scientists discover places on the moon where it's always 'sweater weather'

Future human explorers on the moon might have 99 problems but staying warm or cool won't be one. A team led by planetary scientists at UCLA has discovered shady locations within pits on the moon that always hover around a comfortable 63 degrees Fahrenheit.

The pits, and caves to which they may lead, would make safer, more thermally stable base camps for lunar exploration and long-term habitation than the rest of the moon's surface, which heats up to 260 degrees during the day and drops to 280 degrees below zero at night.

Pits were first discovered on the moon in 2009, and since then, scientists have wondered if they led to caves that could be explored or used as shelters. About 16 of the more than 200 pits are probably collapsed lava tubes, said Tyler Horvath, a UCLA doctoral student in planetary science, who led the new research. Two of the most prominent pits have visible overhangs that clearly lead to some sort of cave or void, and there is strong evidence that another's overhang may also lead to a large cave.

Lava tubes, also found on Earth, form when molten lava flows beneath a field of cooled lava or a crust forms over a river of lava, leaving a long, hollow tunnel. If the ceiling of a solidified lava tube collapses, it opens a pit that can lead into the rest of the cavelike tube.

Horvath processed images from the Diviner Lunar Radiometer Experiment -- a thermal camera and one of six instruments on NASA's robotic Lunar Reconnaissance Orbiter -- to find out if the temperature within the pits diverged from those on the surface.

Focusing on a roughly cylindrical 100-meter-deep depression about the length and width of a football field in an area of the moon known as the Mare Tranquillitatis, Horvath and his colleagues used computer modeling to analyze the thermal properties of the rock and lunar dust and to chart the pit's temperatures over a period of time.

The results, recently published in the journal Geophysical Research Letters, revealed that temperatures within the permanently shadowed reaches of the pit fluctuate only slightly throughout the lunar day, remaining at around 63 degrees. If a cave extends from the bottom of the pit, as images taken by the Lunar Reconnaissance Orbiter Camera suggest, it too would have this relatively comfortable temperature.

The research team, which also included UCLA professor of planetary science David Paige and Paul Hayne of the University of Colorado Boulder, believes the shadowing overhang is responsible for the steady temperature, limiting how hot things get during the day and preventing heat from radiating away at night. Meanwhile, the sunbaked part of the pit floor hits daytime temperatures close to 300 degrees, some 40 degrees hotter than the moon's surface.

"Because the Tranquillitatis pit is the closest to the lunar equator, the illuminated floor at noon is probably the hottest place on the entire moon," said Horvath.

A day on the moon lasts nearly 15 Earth days, during which the surface is constantly bombarded by sunlight and is frequently hot enough to boil water. Unimaginably cold nights also last about 15 Earth days. Inventing heating and cooling equipment that can operate under these conditions and producing enough energy to power it nonstop could prove an insurmountable barrier to lunar exploration or habitation. Solar power -- NASA's most common form of power generation -- doesn't work at night, after all. (NASA currently has no plans to establish an exploration base camp or habitations on the moon.)

Building bases in the shadowed parts of these pits allows scientists to focus on other challenges, like growing food, providing oxygen for astronauts, gathering resources for experiments and expanding the base. The pits or caves would also offer some protection from cosmic rays, solar radiation and micrometeorites.

"Humans evolved living in caves, and to caves we might return when we live on the moon," said Paige, who leads the Diviner Lunar Radiometer Experiment.

Diviner has been mapping the moon continuously since 2009, producing NASA's second largest planetary dataset and providing the most detailed and comprehensive thermal measurements of any object in our solar system, including Earth. The team's current work on lunar pits has improved data from the Diviner experiment.

"Because nobody else had looked at things this small with Diviner, we found that it had a bit of double vision, causing all of our maps to a be a bit blurry," said Horvath. The team worked to align the many images taken by the instrument until they could achieve an accurate thermal reading down to the level of single pixel. This process yielded much higher resolution maps of the moon's surface.

Data from the early stages of this lunar pit thermal modeling project were used to help develop the thermal management system of the rover for NASA's proposed Moon Diver mission. Horvath and Hayne were part of the science team for this mission, which aims to have the rover rappel into the Tranquillitatis pit to research the layers of lava flows seen in its walls and to explore any existing cave.

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Volcano's eruption will help scientists plot weather, climate

As it captivated people around the world, the January eruption of the Hunga Tonga-Hunga Ha'apai volcano gave scientists a once-in-a-lifetime chance to study how the atmosphere works, unlocking keys to better predict the weather and changing climate.

The volcano, located in the South Pacific nation of Tonga, became active Dec. 20, 2021, and erupted Jan. 15, 2022. The blast obliterated one of the country's many islands and was described by NASA as more powerful than an atomic bomb.

UMass Lowell's Mathew Barlow, professor of environmental, earth and atmospheric sciences, was among an international team of scientists who studied the atmospheric response to the eruption, the likes of which has never before been recorded. The group's findings were published in Nature.

As part of his work, Barlow created an animated video from satellite data that shows the eruption's dramatic effects. The event saw atmospheric waves pulse around the globe several times and stretch from Earth to the edge of space, some at speeds of 720 mph. The eruption also shot a plume of water vapor, along with volcanic ash, soil and smoke, 31 miles into the air. A short video produced by the researchers summarizes the effects.

"Some of the wave types the Hunga Tonga generated are very important to understanding how the atmosphere works and our ability to make effective computer models for weather forecasting and climate projections," said Barlow, a faculty member in UMass Lowell's Climate Change Initiative. "Through the expulsion of particles into the high atmosphere, some strong eruptions can also have a cooling effect on the climate, though the amount produced by Hunga Tonga does not appear sufficient for a notable climate effect, unlike other volcanic eruptions over the last century, like the Pinatubo eruption in Alaska in 1991."

According to Barlow, the Hunga Tonga explosion appears to be the strongest single burst of volcanic energy released in 140 years, since the eruption of the Krakatoa volcano in Indonesia in 1883. Coupled with advances in satellite imagery, the strength of the Hunga Tonga eruption gave scientists an unprecedented view of atmospheric waves. Barlow said he and fellow researchers were able to analyze its effects in near-real time communication with agencies across the globe.

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Chaos theory provides hints for controlling the weather

Under a project led by the RIKEN Center for Computational Science, researchers have used computer simulations to show that weather phenomena such as sudden downpours could potentially be modified by making small adjustments to certain variables in the weather system. They did this by taking advantage of a system known as a "butterfly attractor" in chaos theory, where a system can have one of two states -- like the wings of a butterfly -- and that it switches back and forth between the two states depending on small changes in certain conditions.

While weather predictions have reached levels of high accuracy thanks to methods such as supercomputer-based simulations and data assimilation, where observational data is incorporated into simulations, scientists have long hoped to be able to control the weather. Research in this area has intensified due to climate change, which has led to more extreme weather events such as torrential rain and storms.

There are methods at present for weather modification, but they have had limited success. Seeding the atmosphere to induce rain has been demonstrated, but it is only possible when the atmosphere is already in a state where it might rain. Geoengineering projects have been envisioned, but have not been carried out due to concerns about what unpredicted long-term effects they might have.

As a promising approach, researchers from the RIKEN team have looked to chaos theory to create realistic possibilities for mitigating weather events such as torrential rain. Specifically, they have focused on a phenomenon known as a butterfly attractor, proposed by mathematician and meteorologist Edward Lorentz, one of the founders of modern chaos theory. Essentially, this refers to a system that can adopt one of two orbits that look like the wings of a butterfly, but can change the orbits randomly based on small fluctuations in the system.

To perform the work, the RIKEN team ran one weather simulation, to serve as the control of "nature" itself, and then ran other simulations, using small variations in a number of variables describing the convection -- how heat moves through the system -- and discovered that small changes in several of the variables together could lead to the system being in a certain state once a certain amount of time elapsed.

According to Takemasa Miyoshi of the RIKEN Center for Computational Science, who led the team, "This opens the path to research into the controllability of weather and could lead to weather control technology. If realized, this research could help us prevent and mitigate extreme windstorms, such as torrential rains and typhoons, whose risks are increasing with climate change."

"We have built a new theory and methodology for studying the controllability of weather," he continues. "Based on the observing system simulation experiments used in previous predictability studies, we were able to design an experiment to investigate predictability based on the assumption that the true values (nature) cannot be changed, but rather that we can change the idea of what can be changed (the object to be controlled)."

Looking to the future, he says, "In this case we used an ideal low-dimensional model to develop a new theory, and in the future we plan to use actual weather models to study the possible controllability of weather."

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Researchers use artificial intelligence to unlock extreme weather mysteries

From lake-draining drought in California to bridge-breaking floods in China, extreme weather is wreaking havoc. Preparing for weather extremes in a changing climate remains a challenge, however, because their causes are complex and their response to global warming is often not well understood. Now, Stanford researchers have developed a machine learning tool to identify conditions for extreme precipitation events in the Midwest, which account for over half of all major U.S. flood disasters. Published in Geophysical Research Letters, their approach is one of the first examples using AI to analyze causes of long-term changes in extreme events and could help make projections of such events more accurate.

"We know that flooding has been getting worse," said study lead author Frances Davenport, a PhD student in Earth system science in Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). "Our goal was to understand why extreme precipitation is increasing, which in turn could lead to better predictions about future flooding."

Among other impacts, global warming is expected to drive heavier rain and snowfall by creating a warmer atmosphere that can hold more moisture. Scientists hypothesize that climate change may affect precipitation in other ways, too, such as changing when and where storms occur. Revealing these impacts has remained difficult, however, in part because global climate models do not necessarily have the spatial resolution to model these regional extreme events.

"This new approach to leveraging machine learning techniques is opening new avenues in our understanding of the underlying causes of changing extremes," said study co-author Noah Diffenbaugh, the Kara J Foundation Professor in the School of Earth, Energy & Environmental Sciences. "That could enable communities and decision makers to better prepare for high-impact events, such as those that are so extreme that they fall outside of our historical experience."

Davenport and Diffenbaugh focused on the upper Mississippi watershed and the eastern part of the Missouri watershed. The highly flood-prone region, which spans parts of nine states, has seen extreme precipitation days and major floods become more frequent in recent decades. The researchers started by using publicly available climate data to calculate the number of extreme precipitation days in the region from 1981 to 2019. Then they trained a machine learning algorithm designed for analyzing grid data, such as images, to identify large-scale atmospheric circulation patterns associated with extreme precipitation (above the 95th percentile).

"The algorithm we use correctly identifies over 90 percent of the extreme precipitation days, which is higher than the performance of traditional statistical methods that we tested," Davenport said.

The trained machine learning algorithm revealed that multiple factors are responsible for the recent increase in Midwest extreme precipitation. During the 21st century, the atmospheric pressure patterns that lead to extreme Midwest precipitation have become more frequent, increasing at a rate of about one additional day per year, although the researchers note that the changes are much weaker going back further in time to the 1980s.

However, the researchers found that when these atmospheric pressure patterns do occur, the amount of precipitation that results has clearly increased. As a result, days with these conditions are more likely to have extreme precipitation now than they did in the past. Davenport and Diffenbaugh also found that increases in the precipitation intensity on these days were associated with higher atmospheric moisture flows from the Gulf of Mexico into the Midwest, bringing the water necessary for heavy rainfall in the region.

The researchers hope to extend their approach to look at how these different factors will affect extreme precipitation in the future. They also envision redeploying the tool to focus on other regions and types of extreme events, and to analyze distinct extreme precipitation causes, such as weather fronts or tropical cyclones. These applications will help further parse climate change's connections to extreme weather.

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Major Atlantic ocean current system might be approaching critical threshold

The major Atlantic ocean current, to which also the Gulf stream belongs, may have been losing stability in the course of the last century. This is shown in a new study published in Nature Climate Change. The Atlantic Meridional Overturning Circulation, or AMOC, transports warm water masses from the tropics northward at the ocean surface and cold water southward at the ocean bottom, which is most relevant for the relatively mild temperatures in Europe. Further, it influences weather systems worldwide. A potential collapse of this ocean current system could therefore have severe consequences.

"The Atlantic Meridional Overturning really is one of our planet's key circulation systems," says the author of the study, Niklas Boers from the Potsdam Institute for Climate Impact Research, Freie Universität Berlin and Exeter University. "We already know from some computer simulations and from data from Earth's past, so-called paleoclimate proxy records, that the AMOC can exhibit -- in addition to the currently attained strong mode -- an alternative, substantially weaker mode of operation. This bi-stability implies that abrupt transitions between the two circulation modes are in principle possible."

Loss of dynamical stability could ultimately lead to collapse

It has been shown previously that the AMOC is currently at its weakest in more than a 1000 years. However, so far it has remained an open question whether the observed weakening corresponds to a change in the mean circulation state, or whether it is associated with an actual loss of dynamical stability. "The difference is crucial," says Niklas Boers, "because the loss of dynamical stability would imply that the AMOC has approached its critical threshold, beyond which a substantial and in practice likely irreversible transition to the weak mode could occur."

Long-term observational data of the strength of the AMOC does unfortunately not exist, but the AMOC leaves so-called fingerprints in sea-surface temperature and salinity patterns of the Atlantic ocean. "A detailed analysis of these fingerprints in eight independent indices now suggests that the AMOC weakening during the last century is indeed likely to be associated with a loss of stability," says Boers. "The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse."

In addition to global warming, freshwater inflow is a factor -- which is also linked to climate change

A number of factors are likely important for the phenomenon -- factors that add to the direct effect that the warming of the Atlantic ocean has on its circulation. These include freshwater inflow from the melting of the Greenland ice sheet, melting sea-ice, increasing precipitation and river run-off. Freshwater is lighter than saltwater and reduces the tendency of the water to sink from the surface to greater depths, which is one of the drivers of the overturning.

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Newly discovered African 'climate seesaw' drove human evolution

While it is widely accepted that climate change drove the evolution of our species in Africa, the exact character of that climate change and its impacts are not well understood. Glacial-interglacial cycles strongly impact patterns of climate change in many parts of the world, and were also assumed to regulate environmental changes in Africa during the critical period of human evolution over the last ~1 million years. The ecosystem changes driven by these glacial cycles are thought to have stimulated the evolution and dispersal of early humans.

A paper published in Proceedings of the National Academy of Sciences (PNAS) this week challenges this view. Dr. Kaboth-Bahr and an international group of multidisciplinary collaborators identified ancient El Niño-like weather patterns as the drivers of major climate changes in Africa. This allowed the group to re-evaluate the existing climatic framework of human evolution.

Walking with the rain

Dr. Kaboth-Bahr and her colleagues integrated 11 climate archives from all across Africa covering the past 620 thousand years to generate a comprehensive spatial picture of when and where wet or dry conditions prevailed over the continent. "We were surprised to find a distinct climatic east-west 'seesaw' very akin to the pattern produced by the weather phenomena of El Niño, that today profoundly influences precipitation distribution in Africa," explains Dr. Kaboth-Bahr, who led the study.

The authors infer that the effects of the tropical Pacific Ocean on the so-called "Walker Circulation" -- a belt of convection cells along the equator that impact the rainfall and aridity of the tropics -- were the prime driver of this climate seesaw. The data clearly shows that the wet and dry regions shifted between the east and west of the African continent on timescales of approximately 100,000 years, with each of the climatic shifts being accompanied by major turnovers in flora and mammal fauna.

"This alternation between dry and wet periods appeared to have governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa," explains Dr. Kaboth-Bahr. "The resultant environmental patchwork was likely to have been a critical component of human evolution and early demography as well."

The scientists are keen to point that although climate change was certainly not the sole factor driving early human evolution, the new study nevertheless provides a novel perspective on the tight link between environmental fluctuations and the origin of our early ancestors.

"We see many species of pan-African mammals whose distributions match the patterns we identify, and whose evolutionary history seems to articulate with the wet-dry oscillations between eastern and western Africa," adds Dr. Eleanor Scerri, one of the co-authors and an evolutionary archaeologist at the Max Planck Institute for the Science of Human History in Germany. "These animals preserve the signals of the environments that humans evolved in, and it seems likely that our human ancestors may have been similarly subdivided across Africa as they were subject to the same environmental pressures."

Ecotones: the transitional regions between different ecological zones

The scientists' work suggests that a seesaw-like pattern of rainfall alternating between eastern and western Africa probably had the effect of creating critically important ecotonal regions -- the buffer zones between different ecological zones, such grassland and forest.

"Ecotones provided diverse, resource-rich and stable environmental settings thought to have been important to early modern humans," adds Dr. Kaboth-Bahr. "They certainly seem to have been important to other faunal communities."

To the scientists, this suggests that Africa's interior regions may have been critically important for fostering long-term population continuity. "We see the archaeological signatures of early members of our species all across Africa," says Dr. Scerri, "but innovations come and go and are often re-invented, suggesting that our deep population history saw a constant saw-tooth like pattern of local population growth and collapse. Ecotonal regions may have provided areas for longer term population continuity, ensuring that the larger human population kept going, even if local populations often went extinct."

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What control the height of mountains? Surprisingly, it is not erosion

Which forces and mechanisms determine the height of mountains? A group of researchers from Münster and Potsdam has now found a surprising answer: It is not erosion and weathering of rocks that determine the upper limit of mountain massifs, but rather an equilibrium of forces in the Earth's crust. This is a fundamentally new and important finding for the earth sciences. The researchers report on it in the scientific journal Nature.

The highest mountain ranges on Earth -- such as the Himalayas or the Andes -- arise along convergent plate boundaries. At such plate boundaries two tectonic plates move toward each other, and one of the plates is forced beneath the other into the Earth's mantle. During this process of subduction, strong earthquakes repeatedly occur on the plate interface, and over millions of years mountain ranges are built at the edges of the continents.

Whether the height of mountain ranges is mainly determined by tectonic processes in the Earth's interior or by erosional processes sculpturing the Earth's surface has long been debated in geosciences.

A new study led by Armin Dielforder of GFZ German Research Centre for Geoscience now shows that erosion by rivers and glaciers has no significant influence on the height of mountain ranges. Together with scientists from the GFZ and the University of Münster (Germany), he resolved the longstanding debate by analysing the strength of various plate boundaries and calculating the forces acting along the plate interfaces.

The researchers arrived at this surprising result by calculating the forces along different plate boundaries on the Earth. They used data that provide information about the strength of plate boundaries. These data are derived, for example, from heat flow measurements in the subsurface. The heat flow at convergent plate boundaries is in turn influenced by the frictional energy at the interfaces of the continental plates.

One can imagine the formation of mountains using a tablecloth. If you place both hands under the cloth on the table top and push it, the cloth folds and at the same time it slides a little over the back of your hands. The emerging folds would correspond, for instance, to the Andes, the sliding over the back of the hands to the friction in the underground. Depending on the characteristics of the rock, tensions also build up in the deep underground which are discharged in severe earthquakes, especially in subduction zones.

The researchers collected worldwide data from the literature on friction in the subsurface of mountain ranges of different heights (Himalayas, Andes, Sumatra, Japan) and calculated the resulting stress and thus the forces that lead to the uplift of the respective mountains. In this way they showed that in active mountains the force on the plate boundary and the forces resulting from the weight and height of the mountains are in balance.

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