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The surprise to Dr. Clapham was how closely the findings from the Great Dying matched today’s trends in ocean chemistry. High concentrations of carbon-based gases in the atmosphere are leading to warming, rapid acidification and low-oxygen dead zones in the oceans.

he and Dr. Langdon noted that carbon was being injected into the atmosphere today far faster than during the Permian extinction. As Dr. Knoll put it, “Today, humans turn out to be every bit as good as volcanoes at putting carbon dioxide into the atmosphere.”

Dr. Clapham and his co-author, Jonathan L. Payne, a Stanford geochemist, concluded that animals with skeletons or shells made of calcium carbonate, or limestone, were more likely to die than those with skeletons of other substances. And animals that had few ways of protecting their internal chemistry were more apt to disappear. Being widely dispersed across the planet was little protection against extinction, and neither was being numerous. The deaths happened throughout the ocean. Nor was there any correlation between extinction and how a creature moved or what it ate. Instead, the authors concluded, the animals died from a lack of dissolved oxygen in the water, an excess of carbon dioxide, a reduced ability to make shells from calcium carbonate, altered ocean acidity and higher water temperatures. They also concluded that all these stresses happened rapidly and that each one amplified the effects of the others. That led to a wholesale change in the ocean’s dominant animals within just 200,000 years, or perhaps much less, Dr. Clapham said.

So what happened 252 million years ago to cause those physiological stresses in marine animals? Additional clues from carbon, calcium and nitrogen isotopes of the period, as well as from organic geochemistry, suggest a “perturbation of the global carbon cycle,” the scientists’ second paper concluded — a huge infusion of carbon into the atmosphere and the ocean.

scientists suspect that the answer lies in the biggest volcanic event of the past 500 million years — the eruptions that formed the Siberian Traps, the stairlike hilly region in northern Russia. The eruptions sent catastrophic amounts of carbon gas into the atmosphere and, ultimately, the oceans; that led to long-term ocean acidification, ocean warming and vast areas of oxygen-poor ocean water

Startlingly large amounts of methane are leaking from wells and pipelines in New Mexico, according to a new analysis of aerial data, suggesting that the oil and gas industry may be contributing more to climate change than was previously known.

The study, by researchers at Stanford University, estimates that oil and gas operations in New Mexico’s Permian Basin are releasing 194 metric tons per hour of methane, a planet-warming gas many times more potent than carbon dioxide. That is more than six times as much as the latest estimate from the Environmental Protection Agency.

He and Ms. Chen, a Ph.D. student in energy resources engineering, said they believed their results showed the necessity of surveying a large number of sites in order to accurately measure the environmental impact of oil and gas production.