Current climate models offer our best guess at the effects of increasing carbon dioxide levels on global temperatures. The current best guess is that 2°C rise will be OK, and we might get away with doubling the geological average for carbon dioxide concentration in the atmosphere (anthropogenic inputs have so far increased carbon dioxide concentrations by 33%). The problem has been that all of the models are just that – the only experiment is the one we’re living in, and we’d all be happier if we didn’t visit the worst case scenario with this world…

Only there is experimental data to be found in the geological record… Recently scientists investigating oceanic cores have followed an increase of 70% in carbon dioxide concentration that occured in the Palaeocene-Eocene thermal maximum, 55 million years ago. Unfortunately for our current models, this increase in carbon dioxide levels appears was associated with a global average temperature increase of 7°C – twice what our current best guess models are predicting.

More details: Rice University news release (via Science Daily)