Could humans cause another Paleocene-Eocene Thermal Maximum?

tags: climate change, Science



Think of the Eocene geological epoch, more than 50 million years ago. Carbon dioxide concentrations exceeded 800 parts per million.

Tropical oceans were at 35°C, nearing body temperature; polar oceans were 12°C, which is the temperature of the waters off San Francisco.

There was no Arctic ice. The coral reefs had all but perished. There were no reef fish and the seabed was paved with the remains of foraminifera, a tiny shellfish.

The ocean food web was dominated by minute picoplankton rather than the more substantial diatoms that are the basis of life today: these were creatures just too small to nourish the fish that would then become prey for today’s sharks, tuna, whales, seals and even seabirds.

The message is that cold is good for big creatures. The trade winds around 50 million years ago were feeble, the oceans were poorly ventilated, with huge zones in which oxygen was sparse or non-existent, and sea levels were high.

Then 56 million years ago came a crisis called the Paleocene-Eocene Thermal Maximum: it lasted 200,000 years and temperatures – already high – soared by at least 5° and perhaps 9°C. Ecosystems were disrupted, but extinctions were few: the sea’s animals managed by moving north or south.

Richard Norris of Scripps Institution of Oceanography at the University of California San Diego and colleagues want to use the Eocene 50 million years ago as a model for future possibilities.

They point out in the journal Science that carbon dioxide levels passed the 400 parts per million mark in May 2013 and that if the world carries on burning fossil fuels at the present rate, then the conditions of the greenhouse world of 50 million years ago could be here in just 80 years.





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