The first detailed analysis of an extraordinary climatic and biological record from the seabed near the North Pole shows that 55 million years ago the Arctic Ocean was much warmer than scientists imagined — a Floridian year-round average of 74 degrees.
The findings, published today in three papers in the journal Nature, fill in a blank spot in scientists’ understanding of climate history. And while they show that much remains to be learned about climate change, they suggest that scientists have greatly underestimated the power of heat-trapping gases to warm the Arctic.
Previous computer simulations, done without the benefit of seabed sampling, did not suggest an ancient Arctic that was nearly so warm, the authors said. So the simulations must have missed elements that lead to greater warming. . . .
The new analysis confirms that the Arctic Ocean warmed remarkably 55 million years ago, which is when many scientists say the extraordinary planetwide warm-up called the Paleocene Eocene Thermal Maximum must have been caused by an enormous outburst of heat-trapping, or greenhouse, gases like methane and carbon dioxide. But no one has found a clear cause for the gas discharge. . . .
The samples also chronicle the subsequent cooling, with many ups and downs, that the researchers say began about 45 million years ago and led to the cycles of ice ages and brief warm spells of the last several million years. . . .
The temperatures recorded in the samples, right through the peak of warming 55 million years ago, were consistently about 18 degrees higher than those projected by computer models trying to “backcast” what the Arctic was like at the time, according to one of the papers.
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