The hidden role of the Milky Way in ancient Egyptian mythology

Ancient Egyptians were known for their religious beliefs and astronomical knowledge of the Sun, Moon, and planets, but up until now it has been unclear what role the Milky Way played in Egyptian religion and culture.

A new study by a University of Portsmouth astrophysicist sheds light on the relationship between the Milky Way and the Egyptian sky-goddess Nut.

Nut is goddess of the sky, who is often depicted as a star-studded woman arched over her brother, the earth god Geb.

She protects the earth from being flooded by the encroaching waters of the void, and plays a key role in the solar cycle, swallowing the Sun as it sets at dusk and giving birth to it once more as it rises at dawn.

The paper draws on ancient Egyptian texts and simulations to argue that the Milky Way might have shone a spotlight, as it were, on Nut's role as the sky.

It proposes that in winter, the Milky Way highlighted Nut's outstretched arms, while in summer, it traced her backbone across the heavens.

Associate Professor in Astrophysics, Dr Or Graur, said: "I chanced upon the sky-goddess Nut when I was writing a book on galaxies and looking into the mythology of the Milky Way. I took my daughters to a museum and they were enchanted by this image of an arched woman and kept asking to hear stories about her.

"This sparked my interest and I decided to combine both astronomy and Egyptology to do a double analysis -- astronomical and cross-cultural -- of the sky-goddess Nut, and whether she really could be linked to the Milky Way."

Dr Graur drew from a rich collection of ancient sources including the Pyramid Texts, Coffin Texts, and the Book of Nut and compared them alongside sophisticated simulations of the Egyptian night sky.

He found compelling evidence that the Milky Way highlighted Nut's divine presence.

Furthermore, Dr Graur connected Egyptian beliefs with those of other cultures, showing similarities in how different societies interpret the Milky Way.

He said: "My study also shows that Nut's role in the transition of the deceased to the afterlife and her connection to the annual bird migration are consistent with how other cultures understand the Milky Way. For example, as a spirits' road among different peoples in North and Central America or as the Birds' Path in Finland and the Baltics.

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Arctic could become 'ice-free' within a decade

The Arctic could see summer days with practically no sea ice as early as the next couple of years, according to a new study out of the University of Colorado Boulder.

The findings, published March 5 in the journal Nature Reviews Earth & Environment, suggest that the first ice-free day in the Arctic could occur over 10 years earlier than previous projections, which focused on when the region would be ice-free for a month or more. The trend remains consistent under all future emission scenarios.

By mid-century, the Arctic is likely to see an entire month without floating ice during September, when the region's sea ice coverage is at its minimum. At the end of the century, the ice-free season could last several months a year, depending on future emissions scenarios. For example, under a high-emissions, or business-as-usual, scenario, the planet's northernmost region could become consistently ice-free even in some winter months.

For scientists, an ice-free Arctic doesn't mean there would be zero ice in the water.

Instead, researchers say the Arctic is ice-free when the ocean has less than 1 million square kilometers (386,000 square miles) of ice. The threshold represents less than 20% of what the region's seasonal minimum ice cover was in the 1980s. In recent years, the Arctic Ocean had around 3.3 million square kilometers of sea ice area at its minimum in September.

Alexandra Jahn, associate professor of atmospheric and oceanic sciences and fellow at CU Boulder's Institute of Arctic and Alpine Research, set out to analyze existing literature on sea ice projections. She and her collaborators also analyzed sea ice coverage data from computational climate models to assess how the Arctic might change daily in the future.

They found that the first day when sea ice coverage dips below the 1-square-kilometer threshold would occur on average four years earlier than the monthly averages, but could occur up to 18 years earlier.

"When it comes to communicating what scientists expect to happen in the Arctic, it is important to predict when we might observe the first ice-free conditions in the Arctic, which will show up in the daily satellite data," Jahn said.

The team projected the Arctic Ocean could become ice-free for the first time on a late August or early September day between the 2020s to 2030s under all emissions scenarios.

Jahn said greenhouse gas emissions are the main contributors to sea ice loss. A decrease in snow and ice cover increases the amount of heat from sunlight absorbed by the ocean, exacerbating ice melt and warming in the Arctic.

Sea ice declines have significant impacts on Arctic animals that rely on sea ice for survival, including seals and polar bears. In addition, as the ocean warms up, researchers are concerned that non-native fish could move into the Arctic Ocean. The impact of these invasive species on local ecosystems remains unclear.

Sea ice loss also poses a risk to the communities living near the coastal region. Sea ice plays a significant role in buffering the impacts of ocean waves on the coastal land, Jahn said. As sea ice retreats, ocean waves would get bigger, causing coastal erosion.

While an ice-free Arctic is inevitable, Jahn said future emissions levels will still determine how often the conditions occur. Under an intermediate emissions scenario, a path the current society is on, the Arctic might become ice-free only during late summer and early fall from August to October. But under the highest emissions scenario, the Arctic could be ice-free for up to nine months by late this century.

"This would transform the Arctic into a completely different environment, from a white summer Arctic to a blue Arctic. So even if ice-free conditions are unavoidable, we still need to keep our emissions as low as possible to avoid prolonged ice-free conditions," Jahn said.

The good news: Arctic sea ice is resilient and can return quickly if the atmosphere cools down.

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Polar bears unlikely to adapt to longer summers

More time stranded on land means greater risk of starvation for polar bears, a new study indicates.

During three summer weeks, 20 polar bears closely observed by scientists tried different strategies to maintain energy reserves, including resting, scavenging and foraging.

Yet nearly all of them lost weight rapidly: on average around 1 kilogram, or 2.2 pounds, per day.

Some have speculated that polar bears might adapt to the longer ice-free seasons due to climate warming by acting like their grizzly bear relatives and either rest or eat terrestrial food.

The polar bears in this study tried versions of both strategies -- with little success.

"Neither strategy will allow polar bears to exist on land beyond a certain amount of time. Even those bears that were foraging lost body weight at the same rate as those that laid down," said Charles Robbins, director of the Washington State University Bear Center and co-author of the study in the journal Nature Communications.

"Polar bears are not grizzly bears wearing white coats. They're very, very different."

Usually larger than grizzly bears, adult male polar bears can reach 10 feet in length and weigh 1,500 pounds compared to grizzly bears' 8 feet and 800 pounds.

To maintain that great mass, polar bears rely on the energy-rich fat of seals, which they best catch on the ice.

Little has been known about polar bear energy expenditure and behavior when confined to land, so researchers used collars with video cameras and GPS to track polar bears summering in the western Hudson Bay region of Manitoba, Canada.

They wanted to see what the specialized ice-hunters ate and did during the extended time on land when their preferred seal prey was out of reach.

The researchers also weighed the bears before and after the observation period and measured their energy expenditures.

"We found a real diversity of bear behaviors, and as a result, we saw a diverse range of energy expenditures," said lead author Anthony Pagano, research wildlife biologist with the U.S. Geological Survey Polar Bear Research Program and former WSU post-doctoral researcher.

Many of the adult male polar bears simply laid down to conserve energy, burning calories at rates similar to hibernation.

Others, actively searched for food, consuming bird and caribou carcasses as well as berries, kelp and grasses.

In all, the researchers found a five-fold range in energy expenditure from an adult male that rested 98% of the time to the most active who clocked 330 kilometers (205 miles). Some adult females spent as much as 40% of their time foraging.

Yet all that activity didn't pay off.

"The terrestrial foods did give them some energetic benefit, but ultimately, the bears had to spend more energy to access those resources," said Pagano.

Three polar bears went for long swims -- one swimming 175 kilometers (about 110 miles) across the bay.

Two found carcasses in the water, a beluga and a seal, but neither bear could feed on their finds while swimming nor bring them back to land.

Only one bear out of the 20 gained weight after stumbling across a dead marine mammal on land.

The study focused on the southern-most extent of polar bear range in the western Hudson Bay, where climate warming is likely impacting the bears at a faster rate than other Arctic regions.

The polar bear population in the area has already declined by an estimated 30% since 1987.

This study indicates that polar bears across the Arctic are at risk of starvation as the ice-free period continues to grow.

"As polar bears are forced on land earlier, it cuts into the period that they normally acquire the majority of the energy they need to survive," said Pagano.

"With increased land use, the expectation is that we'll likely see increases in starvation, particularly with adolescents and females with cubs."

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Extremely hot days are warming twice as fast as average summer days in North-West Europe

New study analysed data on near-surface air temperatures recorded for North-West Europe over the past 60 years. The findings show that the maximum temperature of the hottest days is increasing at twice the rate of the maximum temperature of average summer days. The results highlight the need for urgent action by policy makers to adapt essential infrastructure to the impacts of climate change.

New research led by the University of Oxford has found that climate change is causing the hottest days in North-West Europe to warm at double the rate of average summer days. The difference in trends is most pronounced for England, Wales, and Northern France. Worryingly, while current climate models accurately predict the rate of warming for average days, they underestimate the rate at which the hottest days are warming compared to observations.

According to lead researcher Dr Matthew Patterson, from the University of Oxford's Department of Physics, the results indicate that extreme heat events -- such as the UK's record-breaking heatwave last summer -- are likely to become more regular. Dr Patterson said: 'These findings underline the fact that the UK and neighbouring countries are already experiencing the effects of climate change, and that last year's heatwave was not a fluke. Policy makers urgently need to adapt their infrastructure and health systems to cope with the impacts of higher temperatures.'

For the study, published today in Geographical Research Letters, Dr Patterson analysed data from the past 60 years (1960-2021) recording the maximum daily temperature, provided by the European Centre for Medium-Range Weather Forecasts.

Although the maximum recorded temperature varied between years, the overall trend clearly showed that the hottest days for North-West Europe had warmed at twice the rate of average summer days. For England and Wales, the average summer day increased by approximately 0.26°C per decade, whilst the hottest day increased by around 0.58°C per decade. However, this faster warming of the hottest days was not observed to this extent elsewhere in the Northern Hemisphere.

The reason causing this faster warming of the hottest days relative to average summer days is not yet understood. According to Dr Patterson, this may be due to the hottest summer days in North-West Europe often being linked to hot air transported north from over Spain. Because Spain is warming faster than North-West Europe, this means that air carried in from this region is ever more extreme relative to the ambient air in North-West Europe. The hottest days of 2022, for instance, were driven by a plume of hot air carried north from Spain and the Sahara. However, further research is needed to verify this.

Dr Patterson added: 'Understanding the warming rate of the hottest days will be important if we are to improve climate model simulation of extreme events and make accurate predictions about the future intensity of such events. If our models underestimate the rise in extreme temperatures over the coming decades, we will underestimate the impacts this will have.'

Extreme heat has significant negative impacts on many different aspects of society, including energy and transport infrastructure, and agriculture. It also exacerbates conditions including respiratory and cardiovascular diseases, putting a strain on health services.

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Mixing theory, observation to envision warmer world

Climate changes are conjuring a whirlwind ride that seems to present some creatures opportunities to thrive. Scientists scripting supercharged scenarios caution the difference between seasonal coping and long-term adaption is vast -- and tricky to predict.

Michigan State University biologists have studied damselflies -- which resemble dragonflies and are abundant as both predator and prey in wetlands -- to understand what happens throughout their lifecycle from nymph to winged insect, along with what they eat when summers grow warmer and longer.

Their work in this week's Proceedings of the Royal Society B has a twist -- combining seasons of observational and experimental work in the field and lab with input from a theoretical ecologist, a mathematician by training with supersized modeling creds.

The results: A more realistic look at what a hot summer can bring to a nearby pond, and new respect for the blinding speed global warming is bringing.

"We are seeing the pace of climate change is much more rapid than organisms have endured in their evolutionary experience," said co-author Phoebe Zarnetske, an associate professor of integrative biology

PI of the Spatial and Community Ecology (SpaCE) Lab and director, IBEEM. "That rapid pace is going to be even more of an issue with the increase in extreme events like heat waves."

The work in "Life-history responses to temperature and seasonality mediate ectotherm consumer-resource dynamics under climate warming" finds that inserting the right level of data gleaned from field experiences, specifically the effects of seasonal changes in temperature on consumer lifecycles, creates a more robust predator-prey simulation model. The work differs from the findings of similar models with less biological realism that predicted warming trends would doom predators. They see Michigan damselflies surviving climate warming by shifting into a lifecycle similar to their southern relatives -- squeaking out two lifecycles in a season rather than one.

The work developed from first author Laura Twardochleb's work as a PhD student in Zarnetske's lab. She had spent time observing damselflies' one-year lifecycle in Michigan. They emerge as adults from ponds in the spring. They mate, reproduce and the juveniles grow over a year in the pond by eating zooplankton. They make good study subjects, she said, because they thrive both outside and in the laboratory.

Twardochleb, now with the California State Water Resources Control Board, was part of MSU's Ecology, Evolution, and Behavior Program and as a part of that took a class by Chris Klausmeier, MSU Foundation Professor of Plant Biology and Integrative Biology.

She saw that early models projecting how warming climates would affect ectothermic predators were significantly simpler than the nature she was observing. For one thing, the models didn't allow for the north's change of seasons. The models also weren't keeping track of a predator's size and growth rate and changes in their lifecycle with warming.

Meanwhile, Klausmeier, a theoretical ecologist, was recognizing the special sauce an experimentalist brings when creating mathematical models that take assumptions about how organisms behave, grow, birth, die.

"I can make up any model I want unconstrained by reality," Klausmeier said. "But that's a little dangerous because of course you want something related to the real world. When you join with an experimentalist you can bring not just the experimental results and parameters, but also bring the deep natural history and knowledge to the system to know the key variables and constraints."

The work, factoring in a warmer, but still seasonal climate shows how the damselflies can grow and breed more quickly. Creating a model that only allowed the virtual damselflies to live a one-year lifecycle in a warmer world, they burned out and died. Extinction was on the horizon.

But allow the bugs the option of bringing two generations into a season, and thriving was a possibility. "A lot of models said [predators] were going to starve," Twardochleb said. "That's what's exciting -- that we can make models more realistic."

Twardochleb said the work is good groundwork to understand how other species will respond to a warmer world, particularly species like mosquitoes which are both nuisances and potentially carry diseases.

Zarnetske added that the continual challenge will be beyond the idea that different species will be adapting to a new world. Climate change is outpacing that kind of evolution in an unprecedented way. And the weather extremes -- heat waves, droughts, floods -- are a whole variable.

Read more at Science Daily

Sea ice will soon disappear from the Arctic during the summer months -- and it has happened before

The "Last Ice Area" north of Greenland and Canada is the last sanctuary of all-year sea ice in this time of rising temperatures caused by climate change. A new study now suggests that this may soon be over.

Researchers from Aarhus University, in collaboration with Stockholm University and the United States Geological Survey, analyzed samples from the previously inaccessible region north of Greenland.

The sediment samples were collected from the seabed in the Lincoln Sea, part of the "Last Ice Area." They showed that the sea ice in this region melted away during summer months around 10,000 years ago. The research team concluded that summer sea ice melted at a time when temperatures were at a level that we are rapidly approaching again today.

"Climate models have suggested that summer sea ice in this region will melt in the coming decades, but it's uncertain if it will happen in 20, 30, 40 years, or more. This project has demonstrated that we're very close to this scenario, and that temperatures only have to increase a little before the ice will melt," says Christof Pearce, Assistant Professor at the Department of Geoscience, Aarhus University.

The researchers have used data from the Early Holocene period to predict when the sea ice will melt today. During this time period, summer temperatures in the Arctic were higher than today. Although this was caused by natural climate variability opposed to the human-induced warming, it still is a natural laboratory for studying the fate of this region in the immediate future.

In Aarhus the marine samples have been analysed in collaboration with Associate Professor Marianne Glasius and academic technical staff Mads Mørk Jensen from the Department of Chemistry. Among other things, they studied molecules from certain algae that are only produced when there is sea ice. The researchers can thereby determine when summer sea ice was present in the area.

A wake-up call

When the sea ice in the Lincoln Sea begins to melt during the summer months, it can have major consequences for the climate. Where white ice reflects the rays of the sun, a dark sea will absorb more than ten times as much solar energy and thereby increase global warming. Moreover, it can affect ecosystems:

"The sea ice is a base for many ecosystems. The algae we examined are food for fish, fish are food for birds, etc. How will the marine ecosystems be affected globally if the sea ice disappears? We don't know the answer yet," says Henrieka Detlef, an assistant professor at the Department of Geoscience.

According to the researchers from Aarhus University, the study can be interpreted as good and bad news for the climate.

"The bad news is that we can see this happening very soon. The good news is that our data shows the trend is reversible and we can do something about it if we reduce greenhouse gas emissions and set ambitious political goals. If we can keep temperatures stable or perhaps even make them fall, the sea ice would return to the area," says Henrieka Detlef.

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Over 4% of summer mortality in European cities is attributable to urban heat islands

Over four percent of deaths in cities during the summer months are due to urban heat islands, and one third of these deaths could be prevented by reaching a tree cover of 30%, according to a modelling study published in The Lancet and led by the Barcelona Institute for Global Health (ISGlobal), an institution supported by "la Caixa" Foundation. The study results, obtained with data from 93 European cities, highlight the substantial benefits of planting more trees in cities to attenuate the impact of climate change.

Exposure to heat has been associated with premature mortality, cardiorespiratory disease and hospital admissions. This is particularly true for heat waves, but also occurs with moderately high temperatures in summer. Cities are especially vulnerable to higher temperatures. Less vegetation, higher population density, and impermeable surfaces for buildings and roads, including asphalt, lead to a temperature difference between the city and surrounding areas -- a phenomenon called urban heat island. Given the ongoing global warming and urban growth, this effect is expected to worsen over the next decades.

"Predictions based on current emissions reveal that heat-related illness and death will become a bigger burden to our health services over the next decades," says ISGlobal researcher Tamara Iungman, first author of the study.

An international team led by Mark Nieuwenhuijsen, director of the Urban Planning, Environment and Health Initiative at ISGlobal, estimated mortality rates of residents aged over 20 in 93 European cities (a total of 57 million inhabitants), between June and August 2015, and collected data on daily rural and urban temperatures for each city. The analyses were performed at a high-resolution level (areas of 250m x 250m). First, they estimated the premature mortality by simulating a hypothetical scenario without urban heat island. Second, they estimated the temperature reduction that would be obtained by increasing tree cover to 30% and the associated mortality that could be avoided.

"Our goal is to inform local decision-makers about the benefits of integrating green areas into all neighborhoods in order to promote more sustainable, resilient and healthy urban environments," explains Nieuwenhuijsen.

The protective effect of trees

The results show that, from June to August 2015, cities were on average 1.5oC warmer than the surrounding countryside. In total, 6,700 premature deaths could be attributed to hotter urban temperatures, which represents 4.3% of total mortality during the summer months and 1.8% of year-round mortality. One third of these deaths (2,644) could have been prevented by increasing tree cover up to 30%, thereby reducing temperatures. Overall, cities with the highest excess heat-mortality rates were in Southern and Eastern Europe, with these cities benefiting the most from an increase in tree cover.

The study highlights the substantial benefits of planting more trees in cities, although the authors acknowledge that this can be challenging in some cities due to their design, and that tree planting should be combined with other interventions such as green roofs or other temperature-reducing alternatives.

"Our results also show the need to preserve and maintain the trees that we already have because they are a valuable resource and it takes a long time to grow new trees. It is not only about increasing trees in the city, it is also about how they are distributed," says Nieuwenhuijsen.

The analyses were done for 2015 because population data were not available for later years, but, as Iungman points out, the study provides valuable information for adapting our cities and making them more resilient to the health impact of climate change. "Here we only looked at the cooling effect of trees, but making cities greener has many other health benefits, including longer life expectancy, fewer mental health problems and better cognitive functioning," she adds.

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Study offers most detailed glimpse yet of planet's last 11,000 summers and winters

By analyzing Antarctic ice cores, CU Boulder scientists and an international team of collaborators have revealed the most detailed look yet at the planet's recent climactic history, including summer and winter temperatures dating back 11,000 years to the beginning of what is known as the Holocene.

Published today in Nature, the study is the very first seasonal temperature record of its kind, from anywhere in the world.

"The goal of the research team was to push the boundaries of what is possible with past climate interpretations, and for us that meant trying to understand climate at the shortest timescales, in this case seasonally, from summer to winter, year-by-year, for many thousands of years," said Tyler Jones, lead author on the study, and assistant research professor and fellow at the Institute of Arctic and Alpine Research (INSTAAR).

The study also validates one aspect of a long-standing theory about Earth's climate that has not been previously proven: how seasonal temperatures in polar regions respond to Milankovitch cycles. Serbian scientist Milutin Milankovitch hypothesized a century ago that the collective effects of changes in Earth's position relative to the sun -- due to slow variations of its orbit and axis -- are a strong driver of Earth's long-term climate, including the start and end of ice ages (prior to any significant human influence on the climate).

"I am particularly excited that our result confirms a fundamental prediction of the theory used to explain Earth's ice-age climate cycles: that the intensity of sunlight controls summertime temperatures in the polar regions, and thus melt of ice, too," said Kurt Cuffey, a co-author on the study and professor at the University of California Berkeley.

These more highly detailed data on long-term climate patterns of the past also provide an important baseline for other scientists, who study the impacts of human-caused greenhouse gas emissions on our present and future climate. By knowing which planetary cycles occur naturally and why, researchers can better identify the human influence on climate change and its impacts on global temperatures.

"This research is something that humans can really relate to because we partly experience the world through the changing seasons -- documenting how summer and winter temperature varied through time translates to how we understand climate," said Jones.

Finer definition amidst diffusion

Scientists around the world have long studied Earth's past climate using ice cores gathered from the poles. These slender, cylindrical columns of ice, drilled from ancient ice sheets (mostly in Antarctica and Greenland), provide valuable long-term data trapped in time about everything from past atmospheric concentrations of greenhouse gases to past temperatures of the air and oceans.

The West Antarctic Ice Sheet (WAIS) Divide ice core, the longest ice core ever drilled by U.S. researchers, measures 11,171 feet (or over 2 miles) long and 4.8-inches in diameter -- containing data from as old as 68,000 years ago. Ice cores like this one are then carefully cut into smaller sections which can be safely transported to and stored or analyzed in ice core labs around the country -- like the Stable Isotope Lab at CU Boulder.

For this study, researchers analyzed a continuous record of water-isotope ratios from the WAIS ice core. The ratios between the concentration of these isotopes (elements with the same number of protons but different numbers of neutrons) reveal data about past temperatures and atmospheric circulation, including transitions between ice ages and warm periods in Earth's past.

Measuring seasonal changes in our planet's history from ice cores is especially difficult, however, due to the fine detail required for their shorter timescales. A process within ice sheets known as diffusion, or natural smoothing, can blur this needed detail.

These water isotopes tend to not stay in one place in the upper ice sheet, but instead move around in interconnected pathways (similar to the air pockets in Styrofoam) as they change states between vapor and ice, over decades or centuries, before sufficiently solidifying. This process can "blur" the data researchers are trying to examine. But by using the high-quality ice cores from the West Antarctic Ice Sheet, extremely high-resolution measurements and advances in ice core analysis from the past 15 years, the team was able to correct for the diffusion present in the data and complete the study.

"Even beyond that, we had to develop new methods entirely to deal with this data, because no one's ever seen it before. We had to go above and beyond what anyone's done in the past," said Jones.

Studying stable isotopes

While the study details the history of Earth's climate, the work behind it has a history of its own.

For more than three decades, researchers at INSTAAR's Stable Isotope Lab have been studying a variety of stable isotopes -- nonradioactive forms of atoms with unique molecular signatures -- found everywhere from the inside ice cores and the carbon in permafrost to the air in our atmosphere. Jones joined the lab in 2007 as a master's student and has never left.

"I have this distinct memory of walking into my advisor, Jim White's office in about 2013, and showing him that we would be able to pull out summer and winter values in this record for the last 11,000 years -- which is extremely rare. In our understanding, no one had ever done this before," said Jones. "We looked at each other and said, 'Wow, this is going to be a really big deal.'"

It then took almost a decade to figure out the proper way to interpret the data, from ice cores drilled many years before that meeting.

Bruce Vaughn, co-author and a chief scientist on the project, and manager of the Stable Isotope Lab, and Bradley Markle, co-author on the study and assistant professor at INSTAAR and the Department of Geology, were there to collect the ice in West Antarctica that was shipped back and analyzed.

The team's next step is to attempt to interpret high-resolution ice cores in other places -- such as the South Pole and in northeast Greenland, where cores have already been drilled -- to better understand our planet's climate variability.

Read more at Science Daily

Northern Hemisphere summers may last nearly half the year by 2100

 Without efforts to mitigate climate change, summers spanning nearly six months may become the new normal by 2100 in the Northern Hemisphere, according to a new study. The change would likely have far-reaching impacts on agriculture, human health and the environment, according to the study authors.

In the 1950s in the Northern Hemisphere, the four seasons arrived in a predictable and fairly even pattern. But climate change is now driving dramatic and irregular changes to the length and start dates of the seasons, which may become more extreme in the future under a business-as-usual climate scenario.

"Summers are getting longer and hotter while winters shorter and warmer due to global warming," said Yuping Guan, a physical oceanographer at the State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, and lead author of the new study in Geophysical Research Letters, AGU's journal for high-impact, short-format reports with immediate implications spanning all Earth and space sciences.

Guan was inspired to investigate changes to the seasonal cycle while mentoring an undergraduate student, co-author Jiamin Wang. "More often, I read some unseasonable weather reports, for example, false spring, or May snow, and the like," Guan said.

The researchers used historical daily climate data from 1952 to 2011 to measure changes in the four seasons' length and onset in the Northern Hemisphere. They defined the start of summer as the onset of temperatures in the hottest 25% during that time period, while winter began with temperatures in the coldest 25%. Next, the team used established climate change models to predict how seasons will shift in the future.

The new study found that, on average, summer grew from 78 to 95 days between 1952 to 2011, while winter shrank from 76 to 73 days. Spring and autumn also contracted from 124 to 115 days, and 87 to 82 days, respectively. Accordingly, spring and summer began earlier, while autumn and winter started later. The Mediterranean region and the Tibetan Plateau experienced the greatest changes to their seasonal cycles.

If these trends continue without any effort to mitigate climate change, the researchers predict that by 2100, winter will last less than two months, and the transitional spring and autumn seasons will shrink further as well.

"Numerous studies have already shown that the changing seasons cause significant environmental and health risks," Guan said. For example, birds are shifting their migration patterns and plants are emerging and flowering at different times. These phenological changes can create mismatches between animals and their food sources, disrupting ecological communities.

Seasonal changes can also wreak havoc on agriculture, especially when false springs or late snowstorms damage budding plants. And with longer growing seasons, humans will breathe in more allergy-causing pollen, and disease-carrying mosquitoes can expand their range northward.

Going to extremes

This shift in the seasons may result in more severe weather events, said Congwen Zhu, a monsoon researcher at the State Key Laboratory of Severe Weather and Institute of Climate System, Chinese Academy of Meteorological Sciences, Beijing, who was not involved in the new study.

"A hotter and longer summer will suffer more frequent and intensified high-temperature events -- heatwaves and wildfires," Zhu said. Additionally, warmer, shorter winters may cause instability that leads to cold surges and winter storms, much like the recent snowstorms in Texas and Israel, he said.

"This is a good overarching starting point for understanding the implications of seasonal change," said Scott Sheridan, a climate scientist at Kent State University who was not part of the new study.

Read more at Science Daily