Two-thirds of the Arctic coastline is made of permafrost — an environment that is very sensitive to warming temperatures. A new report says erosion is causing these coastline regions to recede by an average of 1.5 feet per year.

Unlike rock shoreline, permafrost loses its structure when it warms above freezing. “Surface air temperatures have reached record levels over the past decade,” the report from an international consortium found. Combine this with weakened permafrost and there’s a recipe for erosion.

AMECAMECA, Mexico — Glaciers that crown a Mexican volcano could disappear by 2015 with scientists pointing to global warming as a chief cause of their demise.

Until recently, the glacial field on Iztaccihuatl, a dormant volcano and one of two white-capped peaks that can be seen from Mexico City, was expected to be gone within a few decades.

But studies show rising world temperatures are melting the glaciers faster than previously thought, said Hugo Delgado, a glaciologist at Mexico City’s UNAM university who thinks the massive blocks of ice will be gone within four years.

“What we’ve seen at Iztaccihuatl is an intense period of glacial retreat in the last few years, which has changed the picture,” Delgado said.

OSLO — Sea temperatures off the Antarctic Peninsula have cooled over the past 12,000 years, according to a study on Wednesday that may help scientists understand the impact of modern global warming on the frozen continent.

Scientists want to learn more about Antarctica because even a thaw of the fringes could raise sea levels and swamp low-lying coasts. The continent, discovered only in 1820, contains enough ice to raise world sea levels by nearly 200 feet.

Antarctic

“In Antarctic science we have been missing good records of sea surface temperatures near the ice sheet,” lead author Amelia Shevenell of University College London and the University of Washington, Seattle, told Reuters.

“We are starting to fill in the gaps,” she said of the study in the journal Nature.

The report, based on biological material in sediments, found that “surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 degrees Celsius (5.4 to 7.2 F) over the past 12,000 years.”

The cooling, caused by shifts in the Earth’s orbit around the sun, cut sea temperatures in the area to around zero Celsius in past decades.

Antarctic

The cooling is now being offset by climate change, the study added, with sea temperatures in recent decades rising at about the same rate as the surface of the Antarctic Peninsula — about 3.4 degrees Celsius per century.

Several Antarctic ice shelves have retreated in the past 30 years, a trend widely blamed by scientists on human emissions of greenhouse gases.

The U.N. panel of climate experts projected in a 2007 report that seas might rise by 7-24 inches this century, more if parts of Antarctic or Greenland ice sheets melted. Antarctica’s ice is too deep frozen to suffer a big thaw.

Shevenell said it was not possible to work out how far temperatures would have to rise to trigger more ice shelf collapse or wider melting.

Wednesday’s study also said the cooler trend was masked by shorter-term swings of between 2 and 4 degrees Celsius, apparently linked in the past 2,000 years to a new, natural influence of tropical Pacific weather patterns.

James Bendle, of the University of Glasgow, wrote in a related article in Nature that the study was a step to help work out the influence of the Pacific weather patterns, which could affect sea level rise if they intensify.

“The coastal areas of Antarctica are sites of strong air-sea-ice interactions that can affect the entire globe, but they remain the least-studied region on Earth with respect to climate variability,” he wrote.

Antarctic Landscape

Antarctic Glacier Grid

Iceberg

Experts fear it might happen regularly, turning forest into warming source

RIO DE JANEIRO — A widespread drought in the Amazon rain forest last year was worse than the “once-in-a-century” dry spell in 2005 and may have a bigger impact on global warming than the United States does in a year, British and Brazilian scientists said on Thursday.

More frequent severe droughts like those in 2005 and 2010 risk turning the world’s largest rain forest from a sponge that absorbs carbon emissions into a source of the gases, accelerating global warming, the report found.

Trees and other vegetation in the world’s forests soak up heat-trapping carbon dioxide as they grow, helping cool the planet, but release it when they die and rot.

“If events like this happen more often, the Amazon rain forest would reach a point where it shifts from being a valuable carbon sink slowing climate change to a major source of greenhouse gases that could speed it up,” said lead author Simon Lewis, an ecologist at the University of Leeds.

The study, published in the journal Science, found that last year’s drought caused rainfall shortages over a 1.16 million square-mile expanse of the forest, compared with 734,000 square miles in the 2005 drought.

It was also more intense, causing higher tree mortality and having three major epicenters, whereas the 2005 drought was mainly focused in the southwestern Amazon.

As a result, the study predicted the Amazon forest would not absorb its usual 1.5 billion metric tons of carbon dioxide from the atmosphere in both 2010 and 2011. In addition, the dead and dying trees would release 5 billion metric tons of the gas in the coming years, making a total impact of about 8 billion metric tons, according to the study.

In comparison, the United States emitted 5.4 billion metric tons of carbon dioxide from fossil fuel use in 2009.

The combined emissions caused by the two droughts were probably enough to have canceled out the carbon absorbed by the forest over the past 10 years, the study found.

The widespread drought last year dried up major rivers in the Amazon and isolated thousands of people who depend on boat transportation, shocking climate scientists who had billed the 2005 drought as a once-in-a-century event.

The two intense dry spells fit predictions by some climate models that the forest will face greater weather extremes this century, with more intense droughts making it more vulnerable to fires, which in turn could damage its ability to recover.

Under the more extreme scenarios, large parts of the forest could turn into a savannah-like ecosystem by the middle of the century with much lower levels of animal and plant biodiversity. Although human-caused deforestation in Brazil has fallen sharply in recent years, scientists say the forest is still vulnerable.

A crucial question is whether the droughts are being driven by higher levels of greenhouse gases or are an anomaly, Lewis said. If they are driven by global warming, a vicious cycle of warmer temperatures and droughts could conceivably lead to a large-scale transformation of the forest over a period of decades.

“You could quite rapidly move to a much drier Amazon with less forest there,” Lewis told Reuters.

The research was a collaboration among scientists at the University of Leeds and the University of Sheffield in Britain and Brazil’s Amazon Environmental Research Institute.

In recent decades documented biological changes in the far Northern Hemisphere have been attributed to global warming, changes from species extinctions to shifting geographic ranges. Such changes were expected because warming has been fastest in the northern temperate zone and the Arctic.

But new research published in the Oct. 7 edition of Nature adds to growing evidence that, even though the temperature increase has been smaller in the tropics, the impact of warming on life could be much greater there than in colder climates.

The study focused on ectothermic, or cold-blooded, organisms (those whose body temperature approximates the temperature of their surroundings). Researchers used nearly 500 million temperature readings from more than 3,000 stations around the world to chart temperature increases from 1961 through 2009, then examined the effect of those increases on metabolism.

“The expectation was that physiological changes would also be greatest in the north temperate-Arctic region, but when we ran the numbers that expectation was flipped on its head,” said lead author Michael Dillon, an assistant professor of zoology and physiology at the University of Wyoming.

Freshwater is flowing into Earth’s oceans in greater amounts every year, a team of researchers has found, thanks to more frequent and extreme storms linked to global warming. All told, 18 percent more water fed into the world’s oceans from rivers and melting polar ice sheets in 2006 than in 1994, with an average annual rise of 1.5 percent.

“That might not sound like much — 1.5 percent a year — but after a few decades, it’s huge,” said Jay Famiglietti, UC Irvine Earth system science professor and principal investigator on the study, which will be published this week in Proceedings of the National Academy of Sciences. He noted that while freshwater is essential to humans and ecosystems, the rain is falling in all the wrong places, for all the wrong reasons.

“In general, more water is good,” Famiglietti said. “But here’s the problem: Not everybody is getting more rainfall, and those who are may not need it. What we’re seeing is exactly what the Intergovernmental Panel on Climate Change predicted — that precipitation is increasing in the tropics and the Arctic Circle with heavier, more punishing storms. Meanwhile, hundreds of millions of people live in semiarid regions, and those are drying up.”