claim: Climate sensitivity can be calculated empirically by comparing past temperature change to natural forcings at the time.
evidence: A study published in the Journal of Geophysical Research in July 2007, titled "Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences", used current climate models to look at the consequences of a global nuclear war involving most or all of the world's current nuclear arsenals (which the authors judged to be one similar to the size of the world's arsenals twenty years earlier).