Past Presents Warning on Greater Warming

Reconstruction of climate events long before the Ice Ages shows that failure to reduce greenhouse gas emissions could eventually lead to temperatures rising by up to 10 degrees.

If the distant past is anything to go by, then climate scientists may have under-estimated the hazards of greenhouse gases, and future global warming could be a lot worse than anybody thought.

The calculation rests on two things.  One is a detailed reconstruction of rising greenhouse gas concentrations and an interlude of dramatic warming 56 million years ago.  The other involves an almost metaphysical concept called “climate sensitivity” − the degree of warming to be expected as carbon dioxide concentrations in the atmosphere double.

It isn’t a simple calculation.  There are all sorts of possible feedbacks that might damp this sensitivity or amplify it, but the climate rule of thumb right now is that it means a 3°C rise.

And on the evidence − reported in Geophysical Research Letters − of the sequence of events deep in the past, it could be a lot more.

“The research shows that climate sensitivity was higher during the past global warm climate than in the current climate.” says Gary Shaffer, an expert in Earth system models, and professor at the University of Magallanes Chile and the Niels Bohr Institute in Copenhagen. “This is bad news for humanity as greater climate sensitivity from warming will further amplify the warming.”

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