Tundra study uncovers impact of climate warming in the Arctic

Scientists are using ring growth data, like these shown in a willow shrub, to assess the age and growth of shrubs in a huge study of the Arctic tundra.
Credit: Isla Myers-Smith

Significant changes in one of Earth’s most important ecosystems are not only a symptom of climate change, but may fuel further warming, research suggests.

One of the biggest studies to date of key vegetation in the Arctic tundra provides strong evidence that dramatic changes in the region are being driven by climate warming.

Studies of tundra shrubs — which act as a barometer of the Arctic environment — show that they grow more when temperatures are warmer. Increased shrub growth, driven by recent and future warming in the Arctic, could cause more warming in tundra ecosystems and for the planet as a whole.

Taller shrubs prevent snow from reflecting heat from the sun back into space, warming Earth’s surface. They can also influence soil temperatures and thaw permafrost. Increased shrubs can change the cycling of nutrients and carbon in soil, affecting its decomposition and the amount of carbon released to the atmosphere. All these factors can contribute to climate warming both in the Arctic and on a global scale.

Shrub species in wet landscapes at mid-latitudes of the Arctic are the most sensitive to climate warming, the study found. These areas are vulnerable to change as they store large amounts of carbon in frozen soil, which could be released by warming and permafrost thaw.

An international team of scientists at 37 sites in nine countries, led by the University of Edinburgh, studied records of shrub growth spanning 60 years by analysing annual growth rings in the plant stems, to explore links between climate and vegetation change.

The study, published in Nature Climate Change, was funded by the International Arctic Science Committee. The findings will help improve models of future changes to tundra ecosystems and the impacts of these changes on the global climate.

Dr Isla Myers-Smith, of the University of Edinburgh’s School of GeoSciences, who co-ordinated the study, said: “Arctic shrub growth in the tundra is one of the most significant examples on Earth of the effect that climate change is having on ecosystems. Our findings show there is a lot of variation across this landscape. Understanding this should help improve predictions of climate change impacts across the tundra.”


Story Source:

The above post is reprinted from materials provided byUniversity of EdinburghNote: Materials may be edited for content and length.


Journal Reference:

  1. Isla H. Myers-Smith, Sarah C. Elmendorf, Pieter S. A. Beck, Martin Wilmking, Martin Hallinger, Daan Blok, Ken D. Tape, Shelly A. Rayback, Marc Macias-Fauria, Bruce C. Forbes, James D. M. Speed, Noémie Boulanger-Lapointe, Christian Rixen, Esther Lévesque, Niels Martin Schmidt, Claudia Baittinger, Andrew J. Trant, Luise Hermanutz, Laura Siegwart Collier, Melissa A. Dawes, Trevor C. Lantz, Stef Weijers, Rasmus Halfdan Jørgensen, Agata Buchwal, Allan Buras, Adam T. Naito, Virve Ravolainen, Gabriela Schaepman-Strub, Julia A. Wheeler, Sonja Wipf, Kevin C. Guay, David S. Hik, Mark Vellend. Climate sensitivity of shrub growth across the tundra biomeNature Climate Change, 2015; DOI: 10.1038/nclimate2697
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Tundra study uncovers impact of climate warming in the Arctic

Polar bears threatened: Experience limited energy savings in summer

A young polar bear stands on pack ice over deep waters in the Arctic Ocean in October 2009, during a major research project headed by the University of Wyoming.
Credit: Shawn Harper

Polar bears are unlikely to physiologically compensate for extended food deprivation associated with the ongoing loss of sea ice, according to one-of-its-kind research conducted by University of Wyoming scientists and others, and published today in the journal Science.

“We found that polar bears appear unable to meaningfully prolong their reliance on stored energy, confirming their vulnerability to lost hunting opportunities on the sea ice — even as they surprised us by also exhibiting an unusual ability to minimize heat loss while swimming in Arctic waters,” says John Whiteman, the UW doctoral student who led the project.

The loss of sea ice in the Arctic, which is outpacing predictions, has raised concern about the future of polar bears, leading to their listing as a globally threatened species under the U.S. Endangered Species Act in 2008. The bears depend on hunting seals on the surface of the sea ice over the continental shelf, most successfully from April to July. In parts of the polar bears’ range, the lengthening period of sea ice retreat from shelf waters — caused by increasing temperatures — can reduce their opportunities to hunt seals, leading to declines in bear nutritional condition.

Some earlier research suggested that polar bears could, at least partially, compensate for longer summer food deprivation by entering a state of lowered activity and reduced metabolic rate similar to winter hibernation — a so-called “walking hibernation.” But the new research shows that the summer activity and body temperature of bears on shore and on ice were typical of fasting, non-hibernating mammals, with little indication of “walking hibernation.”

Whiteman and his colleagues concluded in theSciencepublication: “This suggests that bears are unlikely to avoid deleterious declines in body condition, and ultimately survival, that are expected with continued ice loss and lengthening of the ice-melt period.”

The researchers reached that conclusion by capturing more than two dozen polar bears, implanting temperature loggers and tracking their subsequent movements on shore and on ice in the Arctic Ocean’s Beaufort Sea, north of Alaska and Canada, during 2008-2010. The unprecedented effort, logistically supported by the U.S. Geological Survey (USGS) and funded by the National Science Foundation, USGS, U.S. Fish and Wildlife Service (USFWS), as well as the Environmental Protection Agency, required the assistance of numerous personnel, multiple helicopters and deployment of the U.S. Coast Guard ice-breaker, the Polar Sea.

“Many colleagues — even some on our research team — doubted whether the study was possible, until we actually did it,” says Merav Ben-David, the UW professor who developed the research plan along with Professor Hank Harlow, an eco-physiologist and colleague in the Department of Zoology and Physiology, and Steve Amstrup, previously with the USGS and currently the chief scientist at Polar Bears International. “This project was logistically so intense that it may never be replicated.”

At the same time, the scientists found that polar bears use an unusual physiological response to avoid unsustainable heat loss while swimming in the cold Arctic waters. To maintain an interior body temperature that allows them to survive longer and nowadays more frequent swims, the bears temporarily cool the outermost tissues of their core to form an insulating shell — a phenomenon called regional heterothermy.

“This regional heterothermy may represent an adaption to long-distance swims, although its limits remain unknown,” wrote the scientists, who in an earlier publication — in the journalPolar Biology— noted that one of the bears in the study survived a nine-day, 400-mile swim from shore to ice. When recaptured seven weeks later, the bear had lost 22 percent of her body mass, as well as her cub.

By shedding light on potential mechanisms that facilitated that bear’s survival during her long swim, as well as the overall metabolism and activity of bears, the current study “profoundly contributes to understanding the value of summer habitats used by polar bears in terms of their energetics,” Harlow says. Amstrup adds, “It fills a gap in our otherwise extensive knowledge of polar bear ecology and corroborates previous findings that the key to polar bear conservation is arresting the decline of their sea ice habitat.”

In addition to Whiteman, Ben-David, Harlow and Amstrup, co-authors of theSciencepaper are Research Zoologist George Durner of the USGS Alaska Science Center and Wildlife Biologist Eric Regehr of the USFWS Marine Mammals Management in Alaska, both previously Ph.D. students at UW, who also participated in project development and execution; and Professor Richard Anderson-Sprecher of UW’s Department of Statistics and Research Scientist Shannon Albeke of UW’s Wyoming Geographic Information Science Center, who contributed to data analyses.

Additional support for the project was provided by the UW Program in Ecology and Wyoming NASA Space Grant Consortium. Consultation with key Inuit communities in Alaska and Canada ensured the successful completion of the study.

Source: University of Wyoming. “Polar bears threatened: Experience limited energy savings in summer.” ScienceDaily. ScienceDaily, 16 July 2015

Polar bears threatened: Experience limited energy savings in summer

Arctic sea ice rebound shows resilience

North pole unlikely to be ice-free this summer, say UK scientists, but long-term decline continues

Icebergs in eastern Greenland (Flickr/ Mariusz Kluzniak)

By Megan Darby

Arctic sea ice extent has shrunk 40% since the 1970s, prompting speculation as to when it might disappear altogether.

At a scientific gathering last September, Cambridge University’s Peter Wadhams said it could be as soon as summer 2015.

That’s unlikely, according to UK scientists, after the latest data showed sea ice volume had rebounded from low points in 2010 and 2012.

A study published in Nature Geoscience on Monday found an unusually cool summer in 2013 drove a 41% increase in sea ice volume that year.

Models show Arctic sea ice melting over the long term, UCL scientist and lead author Rachel Tilling said. The latest data shows “it can recover by a significant amount if the melting season is cut short”.

It means the Arctic might be more resilient than previously thought, added Andy Shepherd, professor at UCL and at the University of Leeds.

“Understanding what controls the amount of Arctic sea ice takes us one step closer to making reliable predictions of how long it will last, which is important because it is a key component of Earth’s climate system.

“Although the jump in volume means that the region is unlikely to be ice free this summer, we still expect temperatures to rise in the future, and so the events of 2013 will have simply wound the clock back a few years on the long-term pattern of decline.”

The melting icecap has seen the region opened up to shipping and oil exploration in the summer.

Shell’s controversial drilling plans in the region were put on holdlast week after an icebreaker ship got a gash in the hull.

Source: Arctic sea ice rebound shows resilience  – study

Arctic sea ice rebound shows resilience

A New Record Linked to Climate Change Was Just Set in Greenland. It May Seem Esoteric, But It’s Really Important.

esoteric

Back in early July, unusual warmth helped trigger a sudden and dramatic spike in melting at the surface of Greenland’s ice sheet. Exactly what was happening, and whether the trend would continue, was unclear.

Two weeks later, we now know that while the extent of surface melting is still significantly above average, it has not come close to breaking the record (at least not yet).

At the same time, another significant milestone has been reached: The amount of sunlight reflected by snow on the ice sheet’s surface plummeted during the first week of July to the lowest levels seen in the 16 years that it has been measured by satellite.

Reflectivity of snow is not as esoteric as it may seem. It’s actually an important climate variable — one that played a critical role in Greenland’s record-setting surface melt in July of 2012. At that time, just a little less than 100 percent of the surface experienced melting.

It was an astonishing event, and warm temperatures were partly to blame. But so was another factor: darkening of the snow by soot from wildfires burning many hundreds of miles away. And as you’ll see in a minute, soot may have been a factor this summer too.

esoteric

When snow at the surface melts, and even when it warms just shy of the melting point, it will become darker. This causes its reflectivity, or “albedo,” to drop. Although this summer started out cold and snowy in Greenland, by the second half of June, “temperatures were everywhere markedly higher than average,” according to National Snow and Ice Data Center.

Those warm temperatures, as well as bright, sunny skies, were linked to a dome of unusually high atmospheric pressure that formed over Greenland in June. This was in keeping with a trend in recent decades of higher pressures over Greenland and part of the Central Arctic Ocean during summer.

esoteric

The surface of an ice sheet can also become darker when winds carry soot in from distant wildfires. And, in fact, by early July smoke traveling west from wildfires in Alaska, and drifting east from conflagrations in Canada, converged over Greenland.

We’ll have to wait until data from surface surveys are available to know how much of an impact wildfire soot may have had on the surface of the Greenland Ice Sheet in early July.

We do know that during 2012’s record melting, it turned out to be a key factor.

That year, temperatures at the surface were unusually warm, and those balmy conditions were enhanced by a low layer of clouds consisting of tiny water droplets. The cloud layer was thin enough to allow sunlight to pass through and help melt the surface. At the same time it was also thick enough to trap a significant amount of thermal energy being radiated upward from the surface.

But a study published last year suggests those factors alone probably weren’t enough to cause surface melting in the high, dry central region of the ice sheet. Yet melting happened there too — because soot from distant wildfires had lowered the albedo of the snow below a critical threshold, the researchers found.

And that’s why albedo — however esoteric the concept may seem — is really important.

In fact, global warming, wildfires, albedo, and melting snow and ice, are all potentially tied together in a reinforcing feedback loop. Here’s how:

Warmer temperatures due to human activities have been contributing to increased wildfire activity. This has caused darkening of the snow in Greenland, which — as we’ve seen — has helped lead to increased melting at the ice sheet’s surface. More melting of the ice sheet’s surface decreases its albedo, which causes still more melting. Now, add in more global warming from human activities, and you’ve got more fires, lower albedo, more melting, lower albedo, etc., etc.

In 2012, the biggest spike in surface melting in Greenland occurred about mid way through the warm season. That’s where we’re at right now. I wouldn’t bet on a similar event happening this year, because it would take an extraordinary confluence of events.

Extraordinary, but not impossible.

Source: A New Record Linked to Climate Change Was Just Set in Greenland. It May Seem Esoteric, But It’s Really Important.

A New Record Linked to Climate Change Was Just Set in Greenland. It May Seem Esoteric, But It’s Really Important.