Constantine Alexander's blog

UCLA life scientists present new insights on climate change and species interactions

UCLA life scientists provide important new details on how climate change will affect interactions between species in research published online May 21 in the Journal of Animal Ecology. This knowledge, they say, is critical to making accurate predictions and informing policymakers of how species are likely to be impacted by rising temperatures.

"There is a growing recognition among biologists that climate change is affecting how species interact with one another, and that this is going to have very important consequences for the stability and functioning of ecosystems," said the senior author of the research, Van Savage, an assistant professor of ecology and evolutionary biology and of biomathematics at UCLA. "However, there is still a very limited understanding of exactly what these changes will be. Our paper makes progress on this very important question."

Climate change is causing global increases in mean temperature, as well as more fluctuations and greater variability in temperature. Growing evidence suggests these changes are altering when and how species interact, and even which species are able to interact without going extinct, Savage said.

Already, climatic warming is rapidly altering the timing and rate of flowering in plants, as well as breeding and migration in animals — changes that are likely to disrupt interactions between species.

"These changes may bring about novel and potentially unstable species interactions by causing warm-adapted species to seek out geographic regions and to experience seasonal periods that have historically been too cold for them until temperatures begin to rise," said lead author Anthony Dell, a former UCLA postdoctoral researcher now at Germany's University of Gottingen.

Such changes could destabilize entire ecosystems, such as rainforests or coral reefs, said co-author Samraat Pawar, a former UCLA postdoctoral researcher currently at the University of Chicago, who noted that although biologists are becoming increasingly aware that changes in species interactions are likely to be one of most important biological impacts of climate change, they have found it challenging to understand and predict.

Savage's research team has recently made significant progress on this front by developing a biotraits database. This massive dataset has been compiled from the literature and has been standardized and organized so that data can be combined and compared. This group has already used statistical analysis and mechanistic mathematical models to provide information on how various biological traits of organisms respond to changes in temperature and other environmental factors.

In particular, Savage and his team have looked at the impact temperature changes can have on the rate at which an organism uses energy, known as the metabolic rate. This fundamental process governs many aspects of an organism's life, including how much food it will eat, how fast it can move, how much it sleeps and how fast its heart beats. The team makes predictions about how an organism's activity — and thus the broader ecology — are affected by temperature.

In the current research, Savage and his colleagues examined how organisms' different physiological responses to rising temperatures could impact what are known as consumer–resource interactions. These are interactions between two organisms that lead to a "feeding" event — a prime example being a predator (consumer) and its prey (resource). Taken as a whole, a collection of consumer–resource interactions constitutes the food chain or food web that drives the diversity, dynamics and stability of particular communities and ecosystems.

Their model accounts for the fact that a change in temperature is likely to result in some predators becoming better at capturing prey while some prey animals become more efficient at evading capture, leading to imbalances in the food chain and potential repercussions for ecosystems.

A key biological trait driving different responses to temperature change among consumers and resources is body velocity — the speed at which an animal moves. Cold-blooded animals, for example, tend to move faster as their body temperature increases. The biologists predict that one of the primary impacts of global warming will be increasing the amount of time and speed with which organisms move around a landscape and thus encounter and interact with one another.

Specifically, the researchers say, the effects of climatic warming will be determined by the ways in which predators seek their prey — by moving around the landscape in search of mobile prey (active-capture), by remaining stationary and waiting for moving prey (sit-and-wait) or by moving around in search of immobile prey (grazing) — as well as by whether interacting predator–prey species are both cold-blooded, both warm-blooded or one of each.

Because of the effect of temperature on body velocity, biologists predict that encounter rates between predators and prey will increase with rising temperatures if the foraging strategy is active-capture (both predator and prey moving through the landscape), as with an eagle hunting a fish. However, if both species respond to temperature in identical ways, these changes may not lead to significant shifts in their interactions.

With a sit-and-wait strategy, often used by snakes and lizards, the effects of temperature change would arise primarily via the moving prey species, potentially creating a very strong asymmetry between predator and prey. In this case, the asymmetry may profoundly alter the nature of the interaction, so that the two species have much higher or lower abundances and may no longer be able to coexist in the feeding relationship without one or both going extinct.

Similarly, increasing temperatures are likely to have significant impacts on interactions between warm-blooded and a cold-blooded animals, such as warm-blooded birds that feed on cold-blooded lizards, or snakes that feed on squirrels. In these cases, the internal body temperature of the cold-blooded animal — the lizard or snake — will vary when the climate changes. As a result, the organism's physiology will change and, in turn, influence its body velocity, activity and reaction rates. In contrast, warm-blooded animals, whose body temperature is largely independent of external climate, will not experience much change, again creating an asymmetry between species.

Using the biotraits database, the authors show that trait-specific asymmetries exist in organisms' responses to temperature change and are likely to be a major factor in determining the effects of climate change on species interactions.

Naturally, the researchers say, it is impossible to study all the species on the planet, but with their new mathematical model, predictions can be made about effects of warming on different types of consumer–resource interactions.

"The large diversity of species that make up natural ecosystems mean it is logistically infeasible to study every species interaction in a community and make predictions about how these interactions will be affected by climate warming," Savage noted. "However, models that assume all species respond to temperature in the same way will both miss the large diversity in ecological systems and therefore miss the most important consequences that arise from differential and asymmetric responses to temperature among species."

"In this paper we forge a middle ground between these two extremes," Dell said. "We allow different species to have different thermal responses and show this is essential for predicting species responses to climate change, while also having our categories be much broader than every species on the planet. This new model can help form the foundation for a more predictive framework for understanding the effects of climate change on communities and ecosystems."

Citation: Dell, A. I., Pawar, S., Savage, V. M. (2013), Temperature dependence of trophic interactions are driven by asymmetry of species responses and foraging strategy. Journal of Animal Ecology. doi: 10.1111/1365-2656.12081

Contact: Stuart Wolpert
swolpert@support.ucla.edu
310-206-0511
University of California - Los Angeles 

Climate change and wildfire

Synthesis of recent findings

Concerns continue to grow about the effects of climate change on fire. Wildfires are expected to increase 50 percent across the United States under a changing climate, over 100 percent in areas of the West by 2050 as projected by some studies. Of equal concern to scientists and policymakers alike are the atmospheric effects of wildfire emissions on climate.

A new article published in the journal Forest Ecology and Management by U.S. Forest Service scientists synthesizes recent findings on the interactions between fire and climate and outlines future research needs. Authored by research meteorologists Yongqiang Liu and Scott Goodrick from the Forest Service Southern Research Station (SRS) and Warren Heilman from the Northern Research Station, the article homes in on the effect of emissions from wildfires on long-term atmospheric conditions.

"While research has historically focused on fire-weather interactions, there is increasing attention paid to fire-climate interactions," says Liu, lead author and team leader with the SRS Center for Forest Disturbance Science. "Weather, the day-to-day state of the atmosphere in a region, influences individual fires within a fire season. In contrast, when we talk about fire climate, we're looking at the statistics of weather over a certain period. Fire climate sets atmospheric conditions for fire activity in longer time frames and larger geographic scales."

Wildfires impact atmospheric conditions through emissions of gases, particles, water, and heat. Some of the article focuses on radiative forcing from fire emissions. Radiative forcing refers to the change in net (down minus up) irradiance (solar plus longwave) at the tropopause, the top of the troposphere where most weather takes place.

Smoke particles can generate radiative forcing mainly through scattering and absorbing solar radiation (direct radiative forcing), and modifying the cloud droplet concentrations and lifetime, and hence the cloud radiative properties (indirect radiative forcing). The change in radiation can cause further changes in global temperatures and precipitation.

"Wildfire emissions can have remarkable impacts on radiative forcing," says Liu. "During fire events or burning seasons, smoke particles reduce overall solar radiation absorbed by the atmosphere at local and regional levels. At the global scale, fire emissions of carbon dioxide contribute substantially to the global greenhouse effect."

Other major findings covered in the synthesis include:

• The radiative forcing of smoke particles can generate significant regional climate effects, leading to lower temperatures at the ground surface.
• Smoke particles mostly suppress cloud formation and precipitation. Fire events could lead to more droughts.
• Black carbon, essentially the fine particles of carbon that color smoke, plays different roles in affecting climate. In the middle and lower atmosphere, its presence could lead to a more stable atmosphere. Black carbon plays a special role in the snow-climate feedback loop, accelerating snow melting.

Land surface changes may be triggered that also play into future effects. "Wildfire is a disturbance of ecosystems," says Liu. "Besides the atmospheric impacts, wildfires also modify terrestrial ecosystem services such as carbon sequestration, soil fertility, grazing value, biodiversity, and tourism. The effects can in turn trigger land use changes that in turn affect the atmosphere."

The article concludes by outlining issues that lead to uncertainties in understanding fire-climate interactions and the future research needed to address them.

Reference: Wildland fire emissions, carbon, and climate: Wildfire–climate interactions. Yongqiang Liua, Scott.

Contact: Yongqiang Liu
yliu@fs.fed.us
706-559-4240
USDA Forest Service ‑ Southern Research Station

Abundance and distribution of Hawaiian coral species predicted by model

Abundant corals are shown in a shallow Hawaiian lagoon. Credit: Keoki Stender

Researchers from the University of Hawaii – Manoa (UHM) School of Ocean and Earth Science and Technology (SOEST) developed species distribution models of the six dominant Hawaiian coral species around the main Hawaiian Islands including two species currently under consideration as threatened or endangered. They found the order of coral abundance (from highest to lowest) around the main Hawaiian Islands to be Porites lobata, Montipora patula, Pocillopora meandrina, Montipora capitata, Porites compressa, and Montipora flabellata.

Environmental factors (wave energy, shape of the seafloor, water clarity, depth, rugosity (roughness of the seafloor), geological island age, and organic sediment content) are known to influence Hawaiian reefs. However, this is the first study to systematically examine the influence of these factors on the distribution and abundance of coral species across the entire seascape of shallow reefs in the main Hawaiian Islands (MHI).

"Average wave height and maximum wave height were the most influential variables explaining coral abundance in the Hawaiian Islands," reported Erik Franklin, lead author of the study and Assistant Research Professor at the UHM Hawaii Institute of Marine Biology. "Our models also identified relationships between coral cover and island age, depth, sunlight, rugosity, slope, and aspect (direction a slope faces)."

In general, coral cover was predicted to be highest in primarily wave-sheltered coastlines and embayments. Reefs with highest cover were concentrated in Kaneohe Bay on Oahu; the wave-sheltered reefs of Molokai, Lanai, Maui, and Kahoolawe; and the Kohala coast of Hawaii.

To construct the species distribution and abundance models, researchers integrated field surveys for corals (data provided by the US National Park Service and US National Oceanic and Atmospheric Administration) with environmental data of wave exposure (data provided by UHM Department of Ocean and Resources Engineering), benthic geomorphology, and sunlight from 2000 to 2009.

Regional-scale mapping of coral species from these models provide a framework for population modeling and marine spatial planning of Hawaiian coral reefs. The geographic characterization of coral reefs would benefit greatly from the improved coral distribution and abundance information generated from coral distribution models. Data from these models can be incorporated into marine conservation plans or used for threat assessments to reefs.

"For example," Franklin says, "our results were recently used in the management plan review process of the Hawaiian Islands Humpback Whale National Marine Sanctuary as they considered the distribution and abundance of animals other than whales."

One advantage of this integrative, modeling approach is that researchers are able to consider a broader range of areas than field surveys alone and, therefore, can provide a truer picture of total abundance. "We were most surprised at the high relative abundance of Montipora patula which is currently under consideration for listing as a threatened or endangered species," reported Franklin. Montipora flabellata, the other coral species under consideration as a threatened or endangered species, was not as abundant as the other five species.

Franklin and colleagues are in the process of extending the modeling approach to include additional marine species in Hawaii such as reef fish and include additional environmental variables to try to improve the predictive capacity of the models. Ideally the results will continue to inform marine resource management in the Hawaiian Islands.

Citation: E C Franklin, P L Jokiel, M J Donahue (2013). Predictive modeling of coral distribution and abundance in the Hawaiian Islands. Marine Ecology Progress Series, 481:121-132; doi: 10.3354/meps10252.

Funding for this research was provided by The National Marine Sanctuary Program, the US Environmental Protection Agency Science To Achieve Results PhD Fellowship, and the US National Science Foundation.

Contact: Marcie Grabowski
mworkman@hawaii.edu
808-956-3151
University of Hawaii ‑ SOEST

WCS informs discussion of responses to a changing Arctic

Increased numbers of walrus on haul-outs are being observed due to receding summer sea ice in the Arctic. As many as 100,000 have been reported on land at one time at Cape Serdtse-Kamen (Chukotka, Russian Federation). Credit: Chukot-TINRO

In two critical reports released at the Arctic Council Ministerial Meeting in Kiruna, Sweden on May 15th, the scientific expertise of the Wildlife Conservation Society helped inform an international body of senior government officials about changing conditions in the Arctic, and potential responses to those changes.

The scientific reports reviewed by the ministers are products of contributions from various experts, representing a range of knowledge and traditions—including indigenous perspectives.

The first report, entitled "Arctic Biodiversity Assessment – Status and Trends," provides the best available science and traditional ecological knowledge on the status and trends of biodiversity in the Arctic. It looks at all aspects of Arctic biodiversity, including all taxonomic groups and ecosystems, and includes a section on recommendations for conservation actions and policy.

WCS Canada's Associate Conservation Zoologist Dr. Don Reid is the lead author of the "Mammals" chapter of this report, which documents recent and ongoing changes to distribution and abundance of marine and terrestrial mammals, along with an assessment of the likely causes of those changes. In addition, he contributed to the "Synthesis" chapter, which brings together the key findings of all the chapters and lays out recommendations for dealing with trends that have been or may soon be problematic for conservation of species and ecosystems.

Reid summarizes the changes as both negative and positive depending on the species, "The Arctic is changing fast, and for mammals, the changes are most obvious in the shifts in habitat that a warming climate is driving," said Reid. On the oceans, ice creates habitat, but summer ice is disappearing, creating problems for polar bears, walrus and seals, but opportunities for some whales. On land, substantial tundra is changing to shrub land, which means a loss of feeding habitats for some species such as reindeer, but a novel area of expansion for moose."

Reid goes on to point out that, "These climate-driven changes then overlay the various other human-induced forces that Arctic wildlife face. This includes new mines, roads, pipelines, oil and gas developments, and increased industrial pollutants, creating a growing complexity of management issues that will require harmonized regulatory regimes internationally, and greater involvement of northern communities in the conservation of the wildlife which are so crucial to their food security and culture."

A second report, the Arctic Resilience Report (ARR), features the insights of WCS Beringia Director Dr. Martin Robards and makes a science-based assessment of the integrated impacts of change in the Arctic. The report looks at the potential for large shifts in ecosystem services that affect human well-being, and how drivers of change interact to affect the ability of ecosystems and human populations to adapt or transform. In addition, this report offers an evaluation of adaptive strategies.

Dr. Robards is a lead author on the Background/Introduction chapters and the author of Chapter Seven that presents one of four case studies. His chapter discusses the rapid increase in Arctic shipping in the narrow confines of the Bering Strait – the gateway for all vessel traffic passing between the Arctic and Pacific Ocean.

"We found great political challenges for responding to the rapid increase in international vessel traffic in a manner that minimizes risks to the incredible aggregations of marine mammals and the food security of indigenous communities," said Dr. Robards. "However, there are also great opportunities for learning from successful efforts elsewhere such as on the eastern seaboard of the United States where Atlantic right whales have received greater protection through attention to vessel speeds and routing. Through our continuing work in the Arctic, WCS is well-suited to offer a unique perspective on the issue and to be a critical voice in offering science-based solutions to these challenges that benefit from the active engagement of the region's indigenous communities."

Approximately 300 people including ministers, delegates from the eight Arctic states (Canada, Denmark, Finland, Iceland, Norway, Russia, Sweden, and the United States), representatives of indigenous peoples, scientists, and observers gathered in Kiruna to mark the end of the two-year Swedish chairmanship and the beginning of the Canadian chairmanship of the Arctic Council.

The Council is a high level intergovernmental forum promoting cooperation, coordination and interaction among the Arctic States. This includes active involvement by Permanent Participants, including Arctic Indigenous representatives, on common Arctic issues, such as sustainable development and environmental protection.

Contact: Scott Smith
ssmith@wcs.org
718-220-3698
Wildlife Conservation Society

Why we need to put the fish back into fisheries

Atlantic Cod

Overfishing has reduced fish populations and biodiversity across much of the world's oceans. In response, fisheries are increasingly reliant on a handful of highly valuable shellfish. However, new research by the University of York shows this approach to be extremely risky.

The research, published today in the journal Fish and Fisheries, shows that traditional fisheries targeting large predators such as cod and haddock, have declined over the past hundred years. In their place, catches of shellfish such as prawns, scallops and lobsters have rocketed as they begin to thrive in unnaturally predator-low environments often degraded by the passage of trawls and dredges.

In many places, including the UK, shellfish are now the most valuable marine resource. The research by the Environment Department at York suggests that although a shellfish-dominated ecosystem appears beneficial from an economic perspective, it is highly risky. Like simplified agricultural systems, these shellfisheries are unstable in the long-term and at great risk of collapse from disease, species invasions and climate change. Warming and acidification of our oceans due to greenhouse gas emissions is expected to affect shellfish worst. Ocean acidification, in particular, will limit the ability of scallops and other shellfish to form proper shells, and lead to widespread mortality.

Lead author, Leigh Howarth, says: "Prawns are now the most valuable fishery in the UK, with catches currently worth over £110 million a year. But this fishery has come to exist only after we overexploited populations of cod, haddock and other predators. If shellfish now collapsed the social consequences for fishermen would be devastating. There are simply very few remaining species left to target."

The study reports similar findings from all over the world. In the United States and Canada, catches of lobster, scallops and crab have also come to dominate following the collapse of cod. However, disease and climate change again put these species at great risk. While in the Black Sea, Baltic and off the west coast of Africa, overfishing of large predators have caused the ecosystems to become overrun with jellyfish, resulting in severe oxygen depletion and eruptions of hydrogen sulphide, thereby wiping out important food chains across 100,000 square kilometres of seabed.

Co-author Dr Bryce Stewart adds: "Shellfish make a valuable contribution to our fisheries. But we cannot just assume everything is rosy. There is an urgent need for continued improvements in management of finfish fisheries, and an ecosystem approach which rebuilds the diversity, resilience and productivity of our oceans into the future."

Co-author Professor Callum Roberts concludes: "The rise of shellfish has been welcomed by many as a lifeline for the fishing industry. However, such changes are not a result of successful management, but rather a result of management failure, a failure to protect stocks and their habitats in the face of industry innovation and overfishing. This study highlights why the UK needs to urgently act to protect our seas. We need more marine protected areas to stop our seas from becoming a wasteland and to restore the diversity and productivity of fisheries well into the future".

Contact: David Garner
david.garner@york.ac.uk
44-019-043-22153
University of York

Front-row seats to climate change

Amphibians and climate change

By day, insects provide the white noise of the South, but the night belongs to the amphibians. In a typical year, the Southern air hangs heavy from the humidity and the sounds of wildlife.

The Southeast, home to more than 140 species of frogs, toads and salamanders, is the center of amphibian biodiversity in our nation. If the ponds and swamps are the auditorium for their symphonic choruses, the scientists of the U.S. Geological Survey's Amphibian Research and Monitoring Initiative, or ARMI, have front-row seats.

Amphibians, which rely on water for part or all of their life cycle, must adjust to often atypical weather. Some years bring heavy deluges, such as the region's notorious hurricanes, and others bring the transformations that come with drought. Amphibians around the world seem to be experiencing the worst declines documented among vertebrates. While habitat loss is the number one reason for population declines, research suggests that disease, invasive species, contaminants and perhaps other factors contribute to declines in protected areas.

And then there's climate change, another stressor for amphibians to contend with. Climate change projections indicate that rainfall will increasingly come in pulses, with greater deluges and longer periods of drought. Scientists have long suspected that climate change is an important factor in amphibian declines, and resource managers are asking whether conservation measures might help species persist or adapt in a changing climate. Three recent U.S. Geological Survey studies offer some insight into the issue.

Why amphibians?

Amphibians, which are declining throughout the world, play an important role in ecological systems. They eat small creatures, including mosquitos, and they are food themselves for larger creatures, such as birds and snakes. Because amphibians are the middle of the food chain -- and sensitive to environmental disruption because of their aquatic or semi-aquatic lives -- their existence is often used as an indication of ecosystem health.

Scientists in ARMI, a program started by Congress in 2000 in response to concerns about amphibian declines, have been working to unravel the ups and downs of amphibian populations to support effective conservation and resource management decisions. To do this, ARMI scientists and field crews monitor the status of amphibians, research the causes of declines, and scientifically evaluate projects undertaken to sustain these species and their habitats across the country.

Pond life – it's not easy being green!

ARMI scientists looked at a range of amphibian species found in the Southeast and posed the question, "What will happen to their populations under a scenario of changes in rainfall patterns – more deluges alternating with droughts - which is being predicted by current climate models?"

It turns out that understanding how climate affects amphibians requires "thinking like the ponds" in which they live. Amphibians have unique life cycles – most alternate between living in water as juveniles, to maturing and dispersing on land, then returning to water again as adults to mate and lay eggs.

When USGS scientists reviewed what was known about amphibian responses to rainfall, it turned out that both extremes in rainfall – drought and heavy rainfall events – can decrease the number of amphibians. The amphibians' response depends on a balance between these two key factors. If ponds dry up while aquatic juveniles are developing, survival of the next generation is lowered. However, if a deluge occurs at that time, nearby pools that often contain fish will be physically connected with the pools containing juvenile amphibians, and the fish will eat the juveniles.

In essence, the study showed that extreme rainfall events are key to predicting amphibian responses to climate, because such events affect the amount and timing of water in ponds that they depend on. The full review of species' responses was published in March 2013 edition of the journal Biology.

Drought and declining salamanders

Knowing that each species responds to droughts and deluges based on the particulars of their biology, scientists set out to test just how these dynamics played out in the southeastern U.S. by looking at larval mole salamanders in small isolated ponds in St. Mark's National Wildlife Refuge, Florida.

Larval mole salamanders have a similar life cycle to the flatwoods salamander, a federally threatened species found on the refuge. Because it is difficult to study the flatwoods salamander directly, and mole salamanders are ecologically similar, scientists study the mole salamander instead, knowing that whatever affects them will likely impact the flatwoods salamander as well.

In the four years of the study, drought consistently decreased salamander occupancy in ponds. To support young salamanders, rain has to fill a pond during the breeding season and then the pond has to stay filled long enough for larvae to transform into the next life stage. Therefore, scientists confirmed that drought did indeed cause short-term declines in mole salamanders – suggesting that the listed flatwoods salamander may face a similar fate under climate change.

The results of the mole salamander study are published in the April 2013 edition of the journal Wetlands.

Can habitat conservation make a difference for frogs and toads?

To answer this question, USGS scientists examined whether the U.S. Department of Agriculture's Natural Resources Conservation Service Wetlands Reserve Program was helping address the problem. The Wetlands Reserve Program is a voluntary USDA program offering landowners the opportunity to protect, restore, and enhance wetlands on their property. To assess the potential benefit of WRP restoration to amphibians, in this case, frogs and toads, USGS scientists surveyed 30 randomly selected WRP sites and 20 nearby agricultural sites in the Mississippi Delta in northwest Mississippi.

The scientists found that WRP sites had more kinds of species and was home to more numbers of amphibians than the agricultural sites studied. The restoration of wetland hydrology appeared to provide the most immediate benefit to the animals.

The study can be found in the March 2013 edition of the journal Restoration Ecology.

What's next?

With multiple studies pointing to the synergistic role of climate change, disease, habitat change, and other factors in amphibian declines, USGS and its partners are continuing their research to provide information which resource managers can use in making decisions that can help arrest or reverse declines. Additionally, a new study that provides the first-ever broad assessment of amphibian populations in the United States, and the first quantitative estimate of trends for amphibian populations at a continental scale, will be published later in May.

For more information, visit  the USGS Amphibian Monitoring website.

Contact: Hannah Hamilton
hhamilton@usgs.gov
703-648-4356
United States Geological Survey

Former Secretary of State Hillary Rodham Clinton & Harrison Ford Lead Provocative Conversation on Conservation

Former Secretary of State Hillary Clinton and Harrison Ford on stage for Conservation International. Credit: Conservation International

Conservation International Board member Harrison Ford and former Secretary of State Hillary Rodham Clinton took the stage May 15 at Conservation International's 16th Annual New York Dinner to discuss the urgent need to preserve our natural capital. The conversation, which ranged from illegal wildlife trade in Africa to the effects of a changing climate on the Arctic, underscored the direct connection between conservation and our economic and security interests.

 

Research into carbon storage in Arctic tundra reveals unexpected insight into ecosystem resiliency

The US Arctic LTER greenhouse in peak autumn and early winter. Credit: Sadie Iverson (autumn), and Josh Schimel (winter)

When UC Santa Barbara doctoral student Seeta Sistla and her adviser, environmental studies professor Josh Schimel, went north not long ago to study how long-term warming in the Arctic affects carbon storage, they had made certain assumptions.

"We expected that because of the long-term warming, we would have lost carbon stored in the soil to the atmosphere," said Schimel. The gradual warming, he explained, would accelerate decomposition on the upper layers of what would have previously been frozen or near-frozen earth, releasing the greenhouse gas into the air. Because high latitudes contain nearly half of all global soil carbon in their ancient permafrost –– permanently frozen soil –– even a few degrees' rise in temperature could be enough to release massive quantities, turning a carbon repository into a carbon emitter.

"The Arctic is the most rapidly warming biome on Earth, so understanding how permafrost soils are reacting to this change is of major concern globally," Sistla said.

To test their hypothesis, the researchers visited the longest-running climate warming study in the tundra, the U.S. Arctic Long-Term Ecological Research site at Toolik Lake in northern Alaska. This ecosystem-warming greenhouse experiment was started in 1989 to observe the effects of sustained warming on the Arctic environment.

What they initially found was typical of Arctic warming: low-lying, shallow-rooted vegetation giving way to taller plants with deeper roots; greater wood shrub dominance; and increased thaw depth. What they weren't expecting was that two decades of slow and steady warming had not changed the amounts of carbon in the soil, despite changes in vegetation and even the soil food web.

The answer to that mystery, according to Sistla, might be found in the finer workings of the ecosystem: Increased plant growth appears to have facilitated stabilizing feedbacks to soil carbon loss. Their research is published in the recent edition of the journal Nature.

"We hypothesize that net soil carbon hasn't changed after 20 years because warming-accelerated decomposition has been offset by increased carbon inputs to the soil due to a combination of increased plant growth and changing soil conditions," Sistla said.

The increased plant productivity, caused by the warmer temperatures –– on average 2 degrees Celsius in the air and 1 degree in the soil to the permafrost –– has increased plant litter inputs to the soil. Unexpectedly, the soils in the greenhouse experiment developed higher winter temperatures, while the summer warming effect declined.

"These changes reflect a complicated feedback," Sistla said. "Shrubs trap more snow than the lower-lying vegetation, creating warmer winter soil temperatures that further stimulate both decomposers and plant growth. Shrubs also increase summer shading, which appears to have reduced decomposer activity in the surface soil by reducing the greenhouse effect during the summer."

The increased plant growth and deeper thaw, meanwhile, also may have enabled increased carbon availability in the deeper mineral layer that overlies the permafrost. In fact, the researchers found the strongest biological effects of warming at depth, a "biotic awakening," with mineral soil decomposers showing more activity, along with the increased carbon stock at that level. "It's a surprising counterbalance," said Schimel. "It may be that those soil systems are not quite as vulnerable to warming as initially expected."

However, whether or not this phenomenon –– no net loss of soil carbon despite long-term warming –– is a transient phase that will eventually give way to increased decomposition activity and more carbon release, is not yet known. Future studies will include investigation into the mineral soil to determine the age of the carbon, which may in turn yield clues into how the carbon cycle is changing at depth, where the majority of tundra soil carbon is stored.

Funding for this study came from the National Science Foundation Long Term Ecological Research (LTER) Program, DOE Global Change Education Program Graduate Fellowship, a Leal Anne Kerry Mertes scholarship, and Explorer's Club.

According to Sistla and Schimel, this research paradigm validates the NSF LTER program's commitment to supporting long-term experiments, because it creates opportunities for younger scientists to observe effects and condition decades after experiments are established –– results that could not have been foreseen when the experiments were started.

Researchers participating in this study include John C. Moore and Rodney T. Simpson from Colorado State University, Fort Collins; Laura Gough from the University of Texas at Arlington; and Gaius R. Shaver from the Marine Biological Laboratory at Woods Hole, Mass.

Contact: Sonia Fernandez
sonia.fernandez@ia.ucsb.edu
805-893-4765
University of California - Santa Barbara

Sea level: One-third of its rise comes from melting mountain glaciers

The Aletschglacier in Switzerland is a typical valley glacier and the largest one in the Alps. Its volume loss since the middle of the 19th century is well visible from the trimlines to the right of the image. Credit: Frank Paul, UZH

How much all glaciers contribute to global sea-level rise has never been calculated before with this accuracy. An international group of researchers involving two geographers from the University of Zurich has confirmed that melting of glaciers caused about one third of the observed sea-level rise, while the ice sheets and thermal expansion of sea water account for one third each. So far, estimates on the contribution of glaciers have differed substantially. Now 16 scientists from nine countries have compared the data from traditional measurements on the ground with satellite data from the NASA missions ICESat (Ice, Cloud and land Elevation Satellite) and GRACE (Gravity Recovery and Climate Experiment).

Combined with a glacier inventory that is available globally for the first time, the researchers were able to determine the glacier mass changes all over the world much more accurately than before. «The extrapolations of local field measurements to large regions and entire mountain ranges traditionally applied sometimes overestimated the ice loss», describes UZH geographer Frank Paul the findings from the satellite measurements. And his fellow colleague Tobias Bolch adds: «We are well aware of the weaknesses of the individual satellite methods. However, in highly glacierized regions the results obtained using the two different methods agree well. With the mix of methods that have now been tested and applied, we have come a major step closer to determining glacier mass loss with higher precision.»

Meltwater pounded at surface in accumulation zone, Columbia Glacier, Alaska, July 2008. Credit: W. Tad Pfeffer

 

Earlier estimates should be corrected

The results show that almost all glacier regions lost mass in the years 2003 to 2009, most of all in Arctic Canada, Alaska, coastal Greenland, the southern Andes and in the Himalayas. By contrast, the glaciers in Antarctica – smaller ice masses that are not connected to the ice sheet – made scarcely any contribution to sea-level rise during this period. This finding deviates significantly from previous estimates, saying that the Antarctic glaciers caused around 30% of the global ice loss in the period from 1961 to 2004. «However, neither the periods nor the data basis are directly comparable here», adds Bolch, «so we shouldn't make any premature conclusions in this respect.»

The results published in «Science» have important consequences for past studies: Bolch and Paul conclude by recommending that «Earlier global estimates on the contribution of glaciers to sea-level rise should be revised again».

Citation: Alex S. Gardner, Geir Moholdt, J. Graham Cogley, Bert Wouters, Anthony A. Arendt, John Wahr, Etienne Bertier, Regine Hock, W. Tad Pfeffer, Georg Kaser, Stefan R. M. Ligtenberg, Tobias Bolch, Martin J. Sharp, Jon Ove Hagen, Michiel R. van den Broeke, Frank Paul. A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009. Science. May 17, 2013. Doi: 10.1126/science.1234532

The UZH geographers Tobias Bolch and Frank Paul contributed important basic data for the study: digital glacier outlines for the global glacier inventory from different regions in the world for which no precise data were previously available. For example for Alaska, Baffin Island, Greenland, the Alps, high-mountain Asia including the Himalayas as well as own calculations on the mass loss in Greenland and in high-mountain Asia.

Contact: Tobias Bolch
tobias.bolch@geo.uzh.ch
41-446-355-236
University of Zurich

Study reveals scientific consensus on anthropogenic climate change

A comprehensive analysis of peer-reviewed articles on the topic of global warming and climate change has revealed an overwhelming consensus among scientists that recent warming is human-caused.

The study is the most comprehensive yet and identified 4000 summaries, otherwise known as abstracts, from papers published in the past 21 years that stated a position on the cause of recent global warming – 97 per cent of these endorsed the consensus that we are seeing man-made, or anthropogenic, global warming (AGW)

Led by John Cook at the University of Queensland, the study has been published today, Thursday 16 May, in IOP Publishing's journal Environmental Research Letters.

The study went one step further, asking the authors of these papers to rate their entire paper using the same criteria. Over 2000 papers were rated and among those that discussed the cause of recent global warming, 97 per cent endorsed the consensus that it is caused by humans.

The findings are in stark contrast to the public's position on global warming; a 2012 poll* revealed that more than half of Americans either disagree, or are unaware, that scientists overwhelmingly agree that the Earth is warming because of human activity.

John Cook said: "Our findings prove that there is a strong scientific agreement about the cause of climate change, despite public perceptions to the contrary.

"There is a gaping chasm between the actual consensus and the public perception. It's staggering given the evidence for consensus that less than half of the general public think scientists agree that humans are causing global warming.

"This is significant because when people understand that scientists agree on global warming, they're more likely to support policies that take action on it."

In March 2012, the researchers used the ISI Web of Science database to search for peer-reviewed academic articles published between 1991 and 2011 using two topic searches: "global warming" and "global climate change".

After limiting the selection to peer-reviewed climate science, the study considered 11 994 papers written by 29 083 authors in 1980 different scientific journals.

The abstracts from these papers were randomly distributed between a team of 24 volunteers recruited through the "myth-busting" website skepticalscience.com, who used set criteria to determine the level to which the abstracts endorsed that humans are the primary cause of global warming. Each abstract was analyzed by two independent, anonymous raters.

From the 11 994 papers, 32.6 per cent endorsed AGW, 66.4 per cent stated no position on AGW, 0.7 per cent rejected AGW and in 0.3 per cent of papers, the authors said the cause of global warming was uncertain.

Co-author of the study Mark Richardson, from the University of Reading, said: "We want our scientists to answer questions for us, and there are lots of exciting questions in climate science. One of them is: are we causing global warming? We found over 4000 studies written by 10 000 scientists that stated a position on this, and 97 per cent said that recent warming is mostly man made."

Visitors to the skepticalscience.com website also raised the funds required to allow the study to be accessible to the public.

Daniel Kammen, editor-in-chief of the journal Environmental Research Letters, said: ""This paper demonstrates the power of the Environmental Research Letters open access model of operation in that authors working to advance our knowledge of climate science and to engage in a public discourse can guarantee all interested parties have the opportunity to review the same data and findings."

Citation: 'Quantifying the consensus on anthropogenic global warming in the scientific literature' John Cook, Dana Nuccitelli, Sarah A Green, Mark Richardson, Bärbel Winkler, Rob Painting, Robert Way, Peter Jacobs and Andrew Skuce 2013 Environ. Res. Lett. 8 024024. doi:10.1088/1748-9326/8/2/024024

Contact: Michael Bishop
michael.bishop@iop.org
01-179-301-032
Institute of Physics