The early part of the Cenozoic era, which started around 65.5 million years ago witnessed a series of transient global warming events called hyperthermals. The most severe of these was the PETM at the Paleocene-Eocene boundary, around 56 million years ago. Over a period of around 20,000 years, a mere blink of the eye in geological terms, ocean temperatures rose globally by approximately 5°C. There is evidence that the concentration of atmospheric carbon oxide increased, but the phenomena that triggered the event remain controversial.

One possibility is that these hyperthermals were driven by cyclic variations in the eccentricity of Earth’s orbit around the sun. At the cycle peaks, increased temperatures could have caused methane hydrate deposits in the deep sea to release large amounts of methane. Some of this potent greenhouse gas would have entered the atmosphere resulting in further intensification of the climatic warming, which would have continued as the methane was fairly rapidly converted into carbon dioxide in the atmosphere.

Alternatively, it may have been geological processes, unrelated to variation in Earth’s orbit, which could have been the culprit for the warming associated with the PETM. In this scenario, magmatism would have caused the baking of marine organic sediments, leading to the massive release of methane and/or carbon dioxide, possibly through hydrothermal vents, thus initiating the global warming which led to the methane release.

“Determining exactly what triggered the PETM requires very accurate dating of the event itself, to determine whether it occurred during a known maximum in the Earth’s orbital eccentricity” explains Adam Charles, a University of Southampton PhD student supervised by Dr Ian Harding, and first author of the newly published report.

To getter a better grip on the numerical age of the Paleocene-Eocene boundary, the researchers measured radio-isotopes of uranium and lead in the mineral zircon, found as crystals in two volcanic ash horizons deposited during the PETM. These rocks were collected from two locations in Spitsbergen, the largest island of the Svalbard Archipelago in the Arctic.

Based on their data, the researchers dated the Paleocene-Eocene boundary at between 55.728 and 55.964 million years ago, which they believe to be the most accurate estimate to date. Their analyses indicated that the onset of the PETM, unlike those of other Eocene hyperthermals, did not occur at the peak of a 400 thousand year cycle in Earth’s orbital eccentricity. Instead, it occurred on the falling limb of a cycle when warming by the sun would not have been at a maximum.

“Compared to other early Eocene hyperthermals, it appears that the PETM was triggered by a different mechanism, and thus may have involved volcanism. However, a thorough test of this hypothesis will require further detailed dating studies,” Adam concluded.

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Yet global warming may affect the capacity of trees to store carbon by altering forest nitrogen cycling, concludes a study led by Jerry Melillo of the Marine Biological Laboratory (MBL), published recently in Proceedings of the National Academy of Sciences.

The paper summarizes the results of a 7-year study at Harvard Forest in central Massachusetts, in which a section of the forest (about one-quarter of an acre) was artificially warmed about 9oF above ambient, to simulate the amount of climate warming that might be observed by the end of the century without aggressive actions to control greenhouse gas emissions from fossil-fuel burning and deforestation.

The study confirmed, as others have, that a warmer climate causes more rapid decomposition of the organic matter in soil, leading to an increase in carbon dioxide being released to the atmosphere.

But the study also showed, for the first time in a field experiment, that warmer temperatures stimulate the gain of carbon stored in trees as woody tissue, partially offsetting the soil carbon loss to the atmosphere. The carbon gains in trees, the scientists found, is due to more nitrogen being made available to the trees with warmer soil.

“Tree growth in many of the forests in the United States is limited by the lack of nitrogen,” Melillo says. “We found that warming causes nitrogen compounds locked up in soil organic matter to be released as inorganic forms of nitrogen such as ammonium, a common form of nitrogen found in garden fertilizer. When trees take up this inorganic nitrogen, they grow faster and store more carbon.”

Melillo says that the biological processes that link soil warming, increased soil organic matter decay, increased nitrogen availability to trees, and increased tree growth will likely operate together in many temperate and boreal forests — forests found in North America, Europe, Eurasia and much of the developed world. Tree growth in tropical forests is often limited by factors other than nitrogen, so lessons from this new study are not widely relevant in the tropics.

While Melillo thinks that the carbon-nitrogen interactions he is studying at Harvard Forest will help us to make predictions of carbon storage in forest over the coming decades, he adds that “the carbon balance of forest ecosystems in a changing climate will also depend on other factors that will change over the century, such as water availability, the effects of increased temperature on both plant photosynthesis and aboveground plant respiration, and the atmospheric concentration of carbon dioxide.”

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Dr. Jian-Guo Huang, currently a post-doc at the University of Alberta, and colleagues from the University of Quebec at Montreal were interested in assessing whether a potentially extended growing season affects stem xylem formation and growth in black spruce (Picea mariana) in Western Quebec, Canada. They published their findings in the May issue of the American Journal of Botany.

Xylem cells conduct water and nutrients from roots to the leaves, but also provide mechanical support and form the wood of trees. Growth patterns of xylem are of interest to foresters because thicker-walled xylem cells produce denser wood — and aspects of the climate, such as temperature and rainfall, may impact not only the number of cells produced during a growing season, but also cell wall thickness.

By taking microcore samples from black spruce trees at three different latitudes ranging from 47.5o to 50oN in Western Quebec throughout the growing season (May-September) in 2005 and 2006, Huang and colleagues were able to determine when xylem cell production began and ended, as well as the pattern of xylem cell growth. They then compared these data to soil and air temperature and precipitation data gathered from local climate stations.

“Every small wood xylem cell contains meteorological information during its growing process,” Huang commented. “Exploring a series of micro-wood xylem cells helps us understand the macro-climate variability.”

When the authors examined the pattern of xylem cell initiation, they found an interesting correlation with patterns in air temperatures in the two years. Across all three sites, xylem cell production in black spruce trees started earlier in 2006 than in 2005, corresponding with an earlier spring (and warmer May temperatures) in 2006 — indicating a positive relationship between temperature and onset of xylem production.

Temperature affects not only when cells begin to grow, but also the growth patterns of those cells. Xylem cells produced early in the season — earlywood — are large in size with thin walls, while those produced later in the season — latewood — are smaller and have thicker walls.

Despite early warm temperatures in 2006, temperatures for the rest of the growing season were actually lower in June through August compared with 2005. And, correspondingly, Huang and co-authors found that in 2006 black spruce trees stopped producing both early and latewood earlier than in 2005. Consequently there were higher ratios of latewood cells to total xylem cells in 2006, and narrower, less-productive growth rings.

“Our study implies that despite the expected occurrence of earlier phenological development due to early spring climate warming, boreal trees like Picea mariana might not be producing wider rings if cold temperatures occur later in the growing season in June to August,” Huang said. “These results may challenge the view that boreal trees could be benefiting from spring warming to enhance growth.”

Thus, not only is the timing of the onset of spring important, but the amplitude of summer warming temperatures also plays a role in wood production.

Huang and his colleagues intend to further explore how intra-annual xylem formation of other boreal species, particularly broadleaf species, is responding to climate warming and varies across species and sites.

“Because broadleaf species are more limited by precipitation, early spring warming (i.e., early onset of cell production) followed by cold June-August temperatures (i.e., less drought stress) might favor xylem cell production, resulting in wider rings and better growth, when compared with conifers like Picea mariana,” commented Huang. “These different growth responses to climate warming across species might lead to potential changes in forest growth, structure and composition, as well as the whole forest ecosystem productivity, and carbon equilibrium.”

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Rather than peer into the future, they are looking backward, exploring how species alive today survived global warming at the end of the Pleistocene and asking whether their responses provide any guidance for us today.

For his dissertation Brad Oberle, a doctoral candidate in biology in Arts & Sciences at Washington University in St. Louis, delved into the post-Pleistocene history of three species of shootingstars (Dodecatheon).

Dodecatheon is a genus of flowering plant in the Primrose family, the petals of whose nodding flowers flex upward, giving the flowers the appearance of a star falling to earth, trailing flames behind it.

Two of the species, the jeweled shootingstar (D. amethystinum), and French’s shootingstar (D. frenchii), are rare and grow only in cliff habitats.

Are the rare species glacial relicts, species adapted to the cool wet conditions during the Pleistocene that gradually retreated to smaller and smaller refuges as the climate warmed? Or were they ecotypes, local variants of a widespread species, Mead’s shootingstar (D. meadia), that had adapted to cliff microclimates but were genetically similar to Mead’s shootingstar.

“As is typical of science,” says Barbara A. Schaal, PhD, the Mary-Dell Chilton Distinguished Professor of biology in Arts & Sciences, Oberle’s dissertation advisor, and his co-author, “the result was mixed. One species is probably a relict species, and the other is probably an ecotype. Some species responded to warming by migrating but other populations apparently adapted in place.”

The article was published in the April 5th issue of the Proceedings of the National Academy of Science (PNAS).

“It’s a lovely piece of work,” Schaal says.

Why shootingstars?

“On hikes I took as a kid,” says Oberle, who grew up in Missouri, “I noticed it felt very different if you were out in a glade, an open habitat with intense sunshine and high temperatures, than if you were down in a hollow, where it’s more sheltered, cooler and tends to be a lot more moist. I also noticed that the plant communities in these two places also differed a lot.”

“When I was just getting started on my Ph, I read a book called The Terrestrial Natural Communities of Missouri by Paul Nelson.

“One species I learned about, French’s shootingstar, specializes in habitats that occur where ledges overhang the bottom of cliffs. These rock houses, as they’re called, tend to form in sandstone cliffs because of the way sandstone weathers. The cliff habitats are typically damp and shelter other interesting plants, as well.

“And then, flipping through the book, I found the jeweled shootingstar, another rare species, but one that specializes on limestone cliffs. It usually grows on slopes at the top of the cliffs right before the rock face becomes vertical.

“It also tends to grow in little patches on the rock face itself,” says Oberle, who admits both to learning technical climbing to prepare for his fieldwork and to twice falling off cliffs in the field.

“The widespread species, D. meadia, is a real mess,” he says. “It’s a beautiful plant and one that tends to catch a botanist’s eye. And almost every botanist that looks at a population of this plant feels that population is special and unique. When botanists have that reaction, they tend to slap a name on the population and call it a new species. Fifty to 100 names have been thrown onto this one species of shootingstar because it’s so beautiful, and comes up in the spring when everybody wants to go out and botanize,” he says laughing.

“The number of species in the genus is still an open question,” Oberle says, “but a revision of this genus published a few years ago named 18 species of Dodecatheon in the United States. The revision identified three species in the eastern U.S. and those are the species I worked with.”

The relict hypothesis and the ecotype hypothesis

Botanists who believe the rare species of shootingstar are distinct species explain their distribution and ecology as a response to historical climate change.

These species really like cold and moist conditions. They throve throughout the last glacial period.

“If you roll the clock back to 20,000 years ago, St. Louis was 50 to 100 miles from a glacier that was about a mile thick,” Oberle says.

These species were widespread at the last glacial maximum when conditions were cooler, but when the climate started to warm up, they couldn’t adapt, so their ranges shrank and they became stuck — i solated in these cliff habitats.

Other botanists, however, think that the shootingstars are just one big jumbled species. If you find an odd-looking shootingstar in a cliff habitat, it isn’t because it had some special history, but instead because the cliff habitat has unusual characteristics and the process of natural selection produces local variants that are adapted to those characteristics. So the rare species are ecotypes, plants specialized for a particular habitat, not relicts.

What the hypotheses predict

As Oberle realized, these hypotheses make specific predictions that could be falsified by research.

The relict hypothesis predicts that the relict species will be genetically distinct from any other species in the area. It’s doing its own thing and it has its own history and it should be possible to detect that history by looking at patterns of genetic variation.

The relict hypothesis also predicts that far flung populations of the relict species will occur in the same kind of habitat and be genetically more similar to one another than to plants that occur in different habitats, even if those plants are nearby.

The ecotype hypothesis makes a contrasting set of predictions. If the rare species are ecotypes, just local variants of the widespread species, their genomes should not vary markedly from that of another random population of the widespread species.

Further, if the rare populations are ecotypes, they should be more similar genetically to nearby ecotypes than they are to distant ones.

The fieldwork

To distinguish between these hypothesesm Oberle collected shootingstars across the eadtern United States, from Pennsylvania to Texas, and from Georgia up to Minnesota.

“One of the ironies of this project,” he says ruefully, “was that I was doing this research about global warming and I was driving all over the country to do it. But it was a fantastic trip, and I got to see amazing places and meet very generous people.

“At every location, I’d take GPS coordinates, try to get a sense for how big the population of plants was, and then sample the plants in a consistent way.

“I measured a trait called specific leaf area, or the fresh leaf area per unit mass, because it gave me insight into how well the plants were adapted to the habitats where I found them.

“I also grabbed leaves for genetic analysis. I sequenced some DNA from all of the plants, but because DNA sequences don’t vary much between plants, I turned to a technique called amplified fragment-length polymorphism (AFLP). That technique tends to be very sensitive; closely related individuals often have very different AFLP banding patterns.

“And finally, I collected a voucher specimen from every population for the herbarium at the Missouri Botanical Garden,” Oberle says.

Some relicts, some ecotypes

The results, which ultimately emerged from the genetic work, depended on the species.

“Populations of jeweled shootingstar from Wisconsin and from Pennsylvania are genetically distinct from all other shootingstars in North America and very similar to one another even though they are so far apart,” Oberle says.

This suggests the jeweled shootingstar is a relict, a plant that was widespread in the past but whose range has become fragmented and that that now survives only in refuge habitats.

French’s shootingstar, on the other hand, is not genetically distinct from D. meadia at all, even though these plants look different and grow in different habitats. Although earlier work has showed they were genetically adapted to different circumstances, overall their genomes are very much alike. So French’s shootingstar is probably just a simple ecotype of D. meadia.

Conservation recommendations

The results suggest that the two rare “species” of shootingstar in the eastern United States should be managed quite differently. Because the jeweled shootingstar is a relict, it’s probably hanging on by a thread. If climate continues to warm, it is likely to go extinct.

“Because we know this species is genetically distinctive, the jeweled shootingstar should be a priority for conservation as climate continues to warm,” Oberle says.

On the other hand, since French’s shootingstar is an ecotype, that suggests that it’s capable of adapting to changing climate.

And, because it isn’t genetically distinctive, a population of French’s shootingstar has the same conservation value as any other random population of D. meadia.

But, Oberle cautions, shootingstars may not respond to human-caused global warming as they did to the warming at the end of the last ice age, both because the warming is more rapid and because the habitat is now fragmented.

The sad part

“I was sad to come to the conclusion that D. frenchii wasn’t really a distinct species, because it is a beautiful plant and it grows in a beautiful habitat, so part of me wanted to recognize the beautiful distinction of it, too.

“My family has owned a farm since the 1860s that is near one of these sandstone cliff habitats. My grandparents and my great-grandparents used to go there in the summertime to rest under the waterfall after working in the fields. And this cliff has a population of D. frenchii, one of the few populations in Missouri. So I have a family connection to this beautiful rare plant, and my research showed it is not as special as we thought it was.

“I felt almost as though I had caused an extinction, although the extinction was just an extinction on paper.”

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“It appears as if farmers in North America got a pass on the first round of global warming,” said David Lobell, an assistant professor of environmental Earth system science at Stanford University. “That was surprising, given how fast we see weather has been changing in agricultural areas around the world as a whole.”

Lobell and his colleagues examined temperature and precipitation records since 1980 for major crop-growing countries in the places and times of year when crops are grown. They then used crop models to estimate what worldwide crop yields would have been had temperature and precipitation had typical fluctuations around 1980 levels.

The researchers found that global wheat production was 5.5 percent lower than it would have been had the climate remained stable, and global corn production was lower by almost 4 percent. Global rice and soybean production were not significantly affected.

The United States, which is the world’s largest producer of soybeans and corn, accounting for roughly 40 percent of global production, experienced a very slight cooling trend and no significant production impacts.

Outside of North America, most major producing countries were found to have experienced some decline in wheat and corn (or maize) yields related to the rise in global temperature. “Yields in most countries are still going up, but not as fast as we estimate they would be without climate trends,” Lobell said.

Lobell is the lead author of a paper about the research to be published May 5 online in Science Express.

Russia, India and France suffered the greatest drops in wheat production relative to what might have been with no global warming. The largest comparative losses in corn production were seen in China and Brazil.

Total worldwide relative losses of the two crops equal the annual production of corn in Mexico and wheat in France. Together, the four crops in the study constitute approximately 75 percent of the calories that humans worldwide consume, directly or indirectly through livestock, according to research cited in the study.

“Given the relatively small temperature trends in the U.S. Corn Belt, it shouldn’t be surprising if complacency or even skepticism about global warming has set in, but this study suggests that would be misguided,” Lobell said.

Since 1950, the average global temperature has increased at a rate of roughly 0.13 degrees Celsius per decade. But over the next two to three decades average global temperature is expected to rise approximately 50 percent faster than that, according to the report of the Intergovernmental Panel on Climate Change. With that rate of temperature change, it is unlikely that the crop-growing regions of the United States will continue to escape the rising temperatures, Lobell said.

“The climate science is still unclear about why summers in the Corn Belt haven’t been warming. But most explanations suggest that warming in the future is just as likely there as elsewhere in the world,” Lobell said.

“In other words, farmers in the Corn Belt seem to have been lucky so far.”

This is the first study to come up with a global estimate for the past 30 years of what has been happening, Lobell said.

To develop their estimates, the researchers used publicly available global data sets from the United Nations Food and Agriculture Organization and from the University of Delaware, University of Wisconsin, and McGill University.

The researchers also estimated the economic effects of the changes in crop yield using models of commodity markets.

“We found that since 1980, the effects of climate change on crop yields have caused an increase of approximately 20 percent in global market prices,” said Wolfram Schlenker, an economist at Columbia University and a coauthor of the paper in Science.

He said if the beneficial effects of higher carbon dioxide levels on crop growth are factored into the calculation, the increase drops down to 5 percent.

“Five percent sounds small until you realize that at current prices world production of these four crops are together worth nearly $1 trillion per year,” Schlenker said. “So a price increase of 5 percent implies roughly $50 billion per year more spent on food.”

Rising commodity prices have so far benefited American farmers, Lobell and Schlenker said, because they haven’t suffered the relative declines in crop yield that the rest of the world has been experiencing.

“It will be interesting to see what happens over the next decade in North America,” Lobell said. “But to me the key message is not necessarily the specifics of each country. I think the real take-home message is that climate change is not just about the future, but that it is affecting agriculture now. Accordingly, efforts to adapt agriculture such as by developing more heat- and drought-tolerant crops will have big payoffs, even today. “

Justin Costa-Roberts, an undergraduate student at Stanford, is also a coauthor of the Science paper. David Lobell is a researcher in Stanford’s Program on Food Security and the Environment, a joint program of Stanford’s Woods Institute for the Environment and Freeman Spogli Institute for International Studies. Schlenker is an assistant professor at the School of International and Public Affairs and at the Department of Economics at Columbia.

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The researchers identified a total of 2,149 barrier islands worldwide using satellite images, topographical maps and navigational charts. The new total is significantly higher than the 1,492 islands identified in a 2001 survey conducted without the aid of publicly available satellite imagery.

All told, the 2,149 barrier islands measure 20,783 kilometers in length, are found along all continents except Antarctica and in all oceans, and make up roughly 10 percent of Earth’s continental shorelines. Seventy-four percent of the islands are found in the northern hemisphere.

Barrier islands help protect low-lying mainland coasts against erosion and storm damage, and can be important wildlife habitats. The nation with the most barrier islands is the United States, with 405, including those along the Alaskan Arctic shoreline.

The survey results appear in the current issue of the peer-reviewed Journal of Coastal Research.

“This provides proof that barrier islands exist in every climate and in every tide-wave combination,” says Orrin H. Pilkey, James B. Duke Professor Emeritus of Geology at Duke’s Nicholas School of the Environment. “We found that everywhere there is a flat piece of land next to the coast, a reasonable supply of sand, enough waves to move sand or sediment about, and a recent sea-level rise that caused a crooked shoreline, barrier islands exist.”

Barrier islands often form as chains of long, low, narrow offshore deposits of sand and sediment, running parallel to a coast but separated from it by bays, estuaries or lagoons. Unlike stationary landforms, barrier islands build up, erode, migrate and rebuild over time in response to waves, tides, currents and other physical processes in the open ocean environment.

The 657 newly identified barrier islands didn’t miraculously appear in the last decade, explains Matthew L. Stutz, assistant professor of geosciences at Meredith, located in Raleigh, N.C. They’ve long existed but were overlooked or misclassified in past surveys.

Previously, for instance, scientists believed barrier islands couldn’t exist in locations with seasonal tides of more than four meters. Yet Stutz and Pilkey’s survey identifies the world’s longest chain of barrier islands along a stretch of the equatorial coast of Brazil, where spring tides reach seven meters.

The 54-island chain extends 571 kilometers along the fringe of a mangrove forest south of the mouth of the Amazon River. Past surveys didn’t recognize it as a barrier island coast partly because older, low-resolution satellite images didn’t show a clear separation between the islands and mangrove, Stutz says, but also because the chain didn’t match the wave-tide criteria used to classify barrier islands in the United States, where most studies have been conducted. Scientists failed to consider that supplies of replenishing sand are so plentiful along the equatorial Brazilian coast that they can compensate for the erosion caused by higher spring tides.

Stutz and Pilkey say the survey’s findings — which formed part of Stutz’s dissertation when he was a doctoral student at Duke — illustrate the need for a new way to classify and study barrier islands, one that takes into account the complex interplay of local, regional and global variables that shape where the islands form and how they evolve.

“Are there clues there to predict which of today’s islands might be in danger of disappearing in the near future?” Stutz asks.

The potential for significant climate and sea level change this century “underscores the need to improve our understanding of the fundamental roles these factors have played historically in island evolution, in order to help us better predict future impacts,” Pilkey says.

“Barrier islands, especially in the temperate zone, are under tremendous development pressure, a rush to the oceanfront that ironically is timed to a period of rising sea levels and shoreline retreat,” he says.

A developed barrier island, held in place by seawalls, jetties or groins, can’t migrate. “It essentially becomes a sitting duck unable to respond to the changes occurring around it.”

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STOCKHOLM (AP) — The world’s military spending grew by only 1.3 percent in 2010, thanks to budget constraints caused by the global financial crisis, with the top three arms investors being the United States, China and Britain, a think–tank said Monday.

South America was the region with the largest military spending growth of 5.8 percent, with countries such as Brazil seeking to increase its international influence, said the Stockholm International Peace Research Institute.

The institution, known as SIPRI, said global military spending in 2010 was the lowest since 2001.

It said the United States topped the list by spending $698 billion last year, followed by China with $119 billion and the United Kingdom with $59.6 billion.

SIPRI said the rise in spending in South America was partly driven by increased staff costs and internal security threats in some countries, but that the change also should be seen in light of the region’s strong economic growth and relatively limited exposure to the world financial crisis.

In many other countries, military investment growth slowed or decreased as governments dealt with budget constraints, SIPRI said.

Arms investment growth in Asia slowed to 1.4 percent, reaching a total of $317 billion, and weapons outlays in Europe fell by 2.8 percent to $382 billion in 2010.

China increased its military expenditures by 3.8 percent in 2010 to $119 billion. That compared to a growth of 15 percent between 2008 and 2009, and SIPRI said the Chinese government had linked its smaller increase in 2010 to the country’s weaker economic performance the year before.

Spending cuts also were noticeable in countries with financial problems such as Greece and the smaller economies in central and eastern Europe, the think–tank said.

The U.S. arms investment growth slowed to 2.8 percent in 2010, compared with a growth of 7.7 percent in 2009. However, the watchdog said the share of U.S. gross domestic product spent on arms increased to 4.8 percent in 2010, from 4.6 percent in 2009, and noted the country accounted for $19.6 billion of the total $20.6 billion global increase in 2010.

“Even in the face of efforts to bring down the soaring U.S. budget deficit, military spending continues to receive privileged treatment,” SIPRI said in the report.

“At 4.8 per cent of GDP, U.S. military spending in 2010 represents the largest economic burden outside the Middle East,” Sam Perlo–Freeman, head of SIPRI’s military expenditure project said. In the Middle East, military expenditures rose by 2.5 percent to $111 billion, mainly supported by Saudi Arabia’s heavy arms spending.

Major oil–producers in Africa, such as Algeria, Angola and Nigeria, also helped increase arms spending in that region by 5.2 percent to $30.1 billion, the think–tank said.

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When faced with high levels of atmospheric carbon dioxide and rising temperatures 56 million years ago, Earth increased its ability to pull carbon from the air. This led to a recovery that was quicker than anticipated by many models of the carbon cycle — though still on the order of tens of thousands of years, said Gabriel Bowen, the associate professor of earth and atmospheric sciences who led the study.

“We found that more than half of the added carbon dioxide was pulled from the atmosphere within 30,000 to 40,000 years, which is one-third of the time span previously thought,” said Bowen, who also is a member of the Purdue Climate Change Research Center. “We still don’t know exactly where this carbon went, but the evidence suggests it was a much more dynamic response than traditional models represent.”

Bowen worked with James Zachos, a professor of earth and planetary sciences at the University of California, Santa Cruz, to study the end of the Palaeocene-Eocene Thermal Maximum, an approximately 170,000-year-long period of global warming that has many features in common with the world’s current situation, he said.

“During this prehistoric event billions of tons of carbon was released into the ocean, atmosphere and biosphere, causing warming of about 5 degrees Celsius,” Bowen said. “This is a good analog for the carbon being released from fossil fuels today.”

Scientists have known of this prehistoric event for 20 years, but how the system recovered and returned to normal atmospheric levels has remained a mystery.

Bowen and Zachos examined samples of marine and terrestrial sediments deposited throughout the event. The team measured the levels of two different types of carbon atoms, the isotopes carbon-12 and carbon-13. The ratio of these isotopes changes as carbon dioxide is drawn from or added to the atmosphere during the growth or decay of organic matter.

Plants prefer carbon-12 during photosynthesis, and when they accelerate their uptake of carbon dioxide it shifts the carbon isotope ratio in the atmosphere. This shift is then reflected in the carbon isotopes present in rock minerals formed by reactions involving atmospheric carbon dioxide, Bowen said.

“The rate of the carbon isotope change in rock minerals tells us how rapidly the carbon dioxide was pulled from the atmosphere,” he said. “We can see the fluxes of carbon dioxide in to and out of the atmosphere. At the beginning of the event we see a shift indicating that a lot of organic-derived carbon dioxide had been added to the atmosphere, and at the end of the event we see a shift indicating that a lot of carbon dioxide was taken up as organic carbon and thus removed from the atmosphere.”

A paper detailing the team’s National Science Foundation-funded work was published in Nature Geoscience.

It had been thought that a slow and fairly constant recovery began soon after excess carbon entered the atmosphere and that the weathering of rocks, called silicate weathering, dictated the timing of the response.

Atmospheric carbon dioxide that reacts with silicon-based minerals in rocks is pulled from the air and captured in the end product of the reaction. This mechanism has a fairly direct correlation with the amount of carbon dioxide in the atmosphere and occurs relatively slowly, Bowen said.

The changes Bowen and Zachos found during the Palaeocene-Eocene Thermal Maximum went beyond the effects expected from silicate weathering, he said.

“It seems there was actually a long period of higher levels of atmospheric carbon dioxide followed by a short and rapid recovery to normal levels,” he said. “During the recovery, the rate at which carbon was pulled from the atmosphere was an order of magnitude greater than the slow drawdown of carbon expected from silicate weathering alone.”

A rapid growth of the biosphere, with a spread of forests, plants and carbon-rich soils to take in the excess carbon dioxide, could explain the quick recovery, Bowen said.

“Expansion of the biosphere is one plausible mechanism for the rapid recovery, but in order to take up this much carbon in forests and soils there must have first been a massive depletion of these carbon stocks,” he said. “We don’t currently know where all the carbon that caused this event came from, and our results suggest the troubling possibility that widespread decay or burning of large parts of the continental biosphere may have been involved.”

Release from a different source, such as volcanoes or sea floor sediments, may have started the event, he said.

“The release of carbon from the biosphere may have occurred as a positive feedback to the warming,” Bowen said. “The forests may have dried out, which can lead to die off and forest fires. If we take the Earth’s future climate to a place where that feedback starts to happen we could see accelerated rates of climate change.”

The team continues to work on new models of the carbon cycle and is also investigating changes in the water cycle during the Palaeocene-Eocene Thermal Maximum.

“We need to figure out where the carbon went all those years ago to know where it could go in the future,” he said. “These findings show that the Earth’s response is much more dynamic than we thought and highlight the importance of feedback loops in the carbon cycle.”

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The search for a single causative factor is often missing the larger picture, they said, and approaches to address the crisis may fail if they don’t consider the totality of causes — or could even make things worse.

No one issue can explain all of the population declines that are occurring at an unprecedented rate, and much faster in amphibians than most other animals, the scientists conclude in a study just published in the Annals of the New York Academy of Sciences.

The amphibian declines are linked to natural forces such as competition, predation, reproduction and disease, as well as human-induced stresses such as habitat destruction, environmental contamination, invasive species and climate change, researchers said.

“An enormous rate of change has occurred in the last 100 years, and amphibians are not evolving fast enough to keep up with it,” said Andrew Blaustein, a professor of zoology at Oregon State University and an international leader in the study of amphibian declines.

“We’re now realizing that it’s not just one thing, it’s a whole range of things,” Blaustein said.

“With a permeable skin and exposure to both aquatic and terrestrial problems, amphibians face a double whammy,” he said. “Because of this, mammals, fish and birds have not experienced population impacts as severely as amphibians — at least, not yet.”

The totality of these changes leads these researchers to believe that Earth is now in a major extinction episode similar to five other mass extinction events in the planet’s history. And amphibians are leading the field — one estimate indicates they are disappearing at more than 200 times that of the average extinction rate.

Efforts to understand these events, especially in the study of amphibians, have often focused on one cause or another, such as fungal diseases, invasive species, an increase in ultraviolet radiation due to ozone depletion, pollution, global warming, and others. All of these and more play a role in the amphibian declines, but the scope of the crisis can only be understood from the perspective of many causes, often overlapping. And efforts that address only one cause risk failure or even compounding the problems, the researchers said.

“Given that many stressors are acting simultaneously on amphibians, we suggest that single-factor explanations for amphibian population declines are likely the exception rather than the rule,” the researchers wrote in their report. “Studies focused on single causes may miss complex interrelationships involving multiple factors and indirect effects.”

One example is the fungus B. dendrobatidis, which has been implicated in the collapse of many frog populations around the world. However, in some populations the fungus causes no problems for years until a lethal threshold is reached, studies have shown.

And while this fungus disrupts electrolyte balance, other pathogens can have different effects such as a parasitic trematode that can cause severe limb malformations, and a nematode that can cause kidney damage. The combination and severity of these pathogens together in a single host, rather than any one individually, are all playing a role in dwindling frog populations.

Past studies at OSU have found a synergistic impact from ultraviolet radiation, which by itself can harm amphibians, and a pathogenic water mold that infects amphibian embryos. And they linked the whole process to water depths at egg-laying sites, which in turn are affected by winter precipitation in the Oregon Cascade Range that is related to climate change.

The problems facing amphibians are a particular concern, scientists say, because they have been one of Earth’s great survivors — evolving about 400 million years ago before the dinosaurs, persisting through ice ages, asteroid impacts, and myriad other ecological and climatic changes.

Their rapid disappearance now suggests that the variety and rate of change exceeds anything they have faced before, the researchers said.

“Modern selection pressures, especially those associated with human activity, may be too severe and may have arisen too rapidly for amphibians to evolve adaptations to overcome them,” the researchers concluded.

This work was supported by the National Science Foundation and the David and Lucile Packard Foundation. Other collaborators on the study were from the University of Colorado, University of Georgia, University of Pittsburgh, and Pepperdine University.

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A major new report has revealed the status of climate change legislation in 16 of the world’s largest economies, including the UK.

It showed that legislation is being advanced among all of these nations, particularly in the last 18 months.

The study was conducted by the Global Legislators Organisation (GLOBE) with the Grantham Research Institute at the London School of Economics and it found that developing countries like Brazil and China are also working at developing legislation to combat climate change.

However, it did find that current legislation is not enough to fully avoid climate change.

Energy secretary Chris Huhne commented: “Low carbon investment needs clear domestic law as well as a comprehensive global agreement.”

He added: “The race is on, and the pioneers are the most likely winners. The international priority must now be to push ahead, building on the progress at Cancun, and work towards a global climate deal.”

Posted by Emily Thomas

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