Saturday round-up: Less ice, more fire

In recent days the extent of sea ice in the Arctic has fallen below the levels seen in 2007, the year with the least sea ice since satellite observations began in 1979. Credit: US National Snow and Ice Data Center

Last week the Arctic Ocean’s ice levels fell below the extent seen at the same time in 2007, which saw the lowest ice cover since satellite observations began in 1979. This comes despite low temperatures in late spring pushing the extent close to the average for the last 20 years of the 20^th Century.

“Cold weather in March caused a late-season spurt in ice growth,” said Mark Serreze, director of the US National Snow and Ice Data Center, ahead of a polar research conference being held next week. “This late season growth, however, consisted of thin ice, which was widely expected to quickly melt out with the onset of spring. While this is exactly what happened, the spring retreat has been especially rapid.”

Serreze has also contributed to a study looking back at sea ice levels in the Arctic over millions of years, emphasising humans’ role in the ice loss currently being seen. Led by Leonid Polyak of Ohio State University, a collaboration of US, Canadian, Swedish, Danish and British researchers brought together findings from nearly 300 previous studies. Taken together, these present one of the most complete pictures yet of the pole’s icy history, published online ahead of print in the journal Quaternary Science Reviews.

“The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades,” Polyak and colleagues write. “This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.”

Much of the data comes from sediment cores collected with great difficulty from the Arctic Ocean floor. These are a record of the debris that has settled at the sea floor, layer by layer, over time. “They record the conditions of the ocean system during the time they settled,” Polyak said on Wednesday. More recent information comes from satellites, and although these are better at determining ice area than thickness, they have provided some disturbing predictions. “Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier,” the team says.

This tree was killed by "understory fire", providing evidence of fire leakage from surrounding farms into the edge of an Amazonian forest in Mato Grosso state, southeast Amazonia. Credit: Luiz Aragão

In warmer climes, the good news that fewer trees are being cut down in the Brazilian Amazon is being undermined by higher numbers of forest fires. That’s according to researchers at the University of Exeter, UK, and Brazil’s National Institute for Space Research writing in the leading journal Science on Friday.

Keeping trees in the Amazon is important as they help sustain the Earth’s ability to remove the greenhouse gas CO2 from the atmosphere naturally. By contrast, removing the trees actually results in the release of carbon to the atmosphere. The UN’s Reducing Emissions from Deforestation and Degradation (UN-REDD) policy has helped reduce deforestation rates in most of the Brazilian Amazon from 2000-2007, Luiz Aragão and Yosio Shimabukuro found. However, in 59% of areas where deforestation rates had fallen there were increased levels of forest fires. “Changes in fire frequency could jeopardise the benefits achieved through UN-REDD,” Aragão said. “Despite UN-REDD’s vital importance in this region, fire is currently neglected in the emerging UN framework.”

These fires are normally caused by farmers who burn their land every three to five years to improve the nutrients in the soil, keeping it fertile enough to produce food. “We need to change the way Amazonian people use and manage their land so that they can do this without fire,” Aragão said.

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