This is a partial repost. I am putting it here because I think the other thread is dying.

There are many papers like the following one. The bottom line is that when we do the numbers in any reasonable type on modeling we have without human driving factors -CO2 is just one of them, we get vastly different results from what is observed, and from models with those factors. The models with those factors are much closer to reality. In short, by doing this process all over the world again and again, we begin to rule out purely “natural” causes for global climate change.

Attribution of polar warming to human influence

Author(s): Gillett NP (Gillett, Nathan P.)1, Stone DA (Stone, Daithi A.)2,3, Stott PA (Stott, Peter A.)4, Nozawa T (Nozawa, Toru)5, Karpechko AY (Karpechko, Alexey Yu.)1, Hegerl GC (Hegerl, Gabriele C.)6, Wehner MF (Wehner, Michael F.)7, Jones PD (Jones, Philip D.)1
Source: NATURE GEOSCIENCE Volume: 1 Issue: 11 Pages: 750-754 Published: NOV 2008

Abstract: The polar regions have long been expected to warm strongly as a result of anthropogenic climate change, because of the positive feedbacks associated with melting ice and snow(1,2). Several studies have noted a rise in Arctic temperatures over recent decades(2-4), but have not formally attributed the changes to human influence, owing to sparse observations and large natural variability(5,6). Both warming and cooling trends have been observed in Antarctica(7), which the Intergovernmental Panel on Climate Change Fourth Assessment Report concludes is the only continent where anthropogenic temperature changes have not been detected so far, possibly as a result of insufficient observational coverage(8). Here we use an up-to-date gridded data set of land surface temperatures(9,10) and simulations from four coupled climate models to assess the causes of the observed polar temperature changes. We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone, and are directly attributable to human influence. Our results demonstrate that human activities have already caused significant warming in both polar regions, with likely impacts on polar biology, indigenous communities(2), ice-sheet mass balance and global sea level(11).