It has been suggested that the forthcoming IPCC AR5 report will claim that it is at least 95% percent likely that human activities – chiefly the burning of fossil fuels – are the main cause of warming since the 1950. Watts Up With That (WUWT) has a new post called when somebody hits you with that new IPCC is 95% certain talking point, show them this. What Anthony wants them to be shown are the two figures below, one showing HADCRUT3 temperature anomalies for 1895-1946 and the other showing temperature anomalies for 1957-2008.
Anthony is suggesting that the warming during the first half of the 20th century is essentially the same as in the second, so how can we claim that the latter warming was almost exclusively anthropogenic. Firstly, they’re not quite the same. The surface temperatures rose faster from 1957-2008 than from 1895-1946, but that’s not all the relevant. A much more appropriate figure is probably the one below. It shows surface temperatures (red), and solar insolation (blue) since 1880. Solar insolation (the amount of solar energy hitting the earth per second) rose during the first half of the 20th century and did indeed dominate the warming (although anthropic influences also existed). However, since about 1960 it’s been dropping while CO2 concentrations and surface temperatures have continued to rise.
So, in a simple sense it is difficult to explain the warming since 1950 as anything other than anthropogenic given that solar insolation has been dropping. There is, however, another issue. Focusing only on surface temperatures when determining if global warming is happening or not, is simplistic. Global warming is about rising energy, not only about rising surface temperatures. Currently we’re accruing energy at a rate of about 1022 J per year (mainly going into the oceans). However, surface temperatures are higher than they’ve been for most of the last 1000 years and are close to being as high as they’ve been for the last 10000 years. Solar insolation is dropping, temperatures are almost as high as they’ve been for thousands of years, so how can we be undergoing some kind of natural global warming? We should be starting to see cooling if the only influences were natural. The only explanation currently available is that the continued warming (i.e., increase in total energy) is because we continue to add CO2 to the atmosphere and it is acting as a greenhouse gas and trapping outgoing long-wavelength radiation.
So, if you want to mislead people about global warming, then show them the two figures Anthony suggests. If you actually want people to understand the current scientific view on global warming, then show them more than simply those two figures. The point is that it is extremely difficult to explain our current warming as anything other than anthropogenic. I suspect that most scientists are certain that it is all anthropogenic. The only reason that it is being framed as 95% likely is simply because scientists tend to acknowledge that maybe there’s something we don’t yet understand or something that we haven’t yet considered. In this case, I suspect that that is highly unlikely.