Earth & Environment

Methane puzzle
After years of climbing, atmospheric concentrations of methane, a potent greenhouse gas, have held steady for nearly 30 years — and for reasons that have not been obvious. Using different data and methods, two new papers in the Aug. 11 Nature link the arrested growth in atmospheric methane with human activities. Chemical markers studied by one U.S. team suggest the plateau traces to a larger global drop in the combustion of fossil fuels during the 1980s than had been recognized. Another group, at the University of California, Irvine, linked much of the change instead to reduced methane emissions from rice production in Asia. —Janet Raloff

 Pumping groundwater raises sea level
The removal of groundwater for drinking, irrigation and other uses appears to have contributed more than 6 percent of the global sea level rise incurred since 1900, a new study finds. Leonard Konikow of the U.S. Geological Survey in Reston, Va., used data sources from around the world to show that over this time, groundwater extraction transferred some 4,500 cubic kilometers into the oceans. And the rate has increased since 1950 — and especially since 2000, when groundwater releases are estimated to have increased sea level some 0.40 millimeters per year. Konikow presents his analyses in a paper that will appear in Geophysical Research Letters. —Janet Raloff

Killer fungus caused extinction
A fungus may have contributed to the world’s great die-off some 250 million years ago. Paleontologists have puzzled over stringy-looking fossils called Reduviasporonites, which appear in rocks deposited worldwide during the mass extinction that ended the Permian period of geologic time. Now, scientists in the Netherlands, England and California suggest the fossils resemble modern-day soil fungi that include many plant pathogens. Fungi spreading through Permian-age plants may thus have helped kill off forests, the scientists proposed online in Geology on Aug. 5. —Alexandra Witze


Beyond Eyjafjallajökull
Europe had better be prepared for more volcanic ash clouds. Prompted by last year’s Eyjafjallajökull eruption in Iceland, a team including Graeme Swindles of the University of Leeds in England searched for signs of volcanic ash that had fallen across northern Europe in the last 7,000 years. Over the last millennium, the team found, ash clouds arrived on average around every 56 years. For any given decade the chance of an ashfall is 16 percent, the scientists reported August 5 in Geology. —Alexandra Witze