 This fascinating figure is from the IPCC. There's a lot of information on here. It includes the things that are changing radiative forcing or changing the climate, how much they're doing so, including the uncertainties, whether they expect the whole globe or just part of it, and the level of scientific understanding. If we do a lot more research, the low probably will reduce the size of the uncertainties because we can learn more, but how much we understand is included in the uncertainties already. And it includes both the things that humans have done and the things that nature has done. And this goes from the year 1750 up to the year 2005. The biggie is our CO2 together with the other greenhouse gases that we've put up, as well as the ozone that comes from human activities from pollution. And so these all have a warming influence, and they are pushing very strongly towards warming. Clearly there's a couple other little warming influences, especially us putting soot on top of snow, but there's also these cooling influences. We have put up a lot of particles, aerosols, that block the sun, and they make clouds last longer and make clouds more effective, more reflective, and together those have a lot of cooling. And we've cut dark forests and replaced them by more reflective grasslands. In addition, since 1750 the sun has brightened a little bit. Over the last 30 years or so it's actually dimmed, but there's a little bit of that. Add all of these together, and there's very clearly a warming influence, and the total warming influence is very similar in size to the CO2 that we've put up. Taken together we are pushing the world in a lot of different ways, but because of these cooling influences, if you ask how much of the warming has been caused by our greenhouse gases, the answer is more than all of it because it is warm despite these cooling influences.