Drafts seen by Reuters of the study by the U.N. panel of experts, due to be published next month, say it is at least 95 percent likely that human activities - chiefly the burning of fossil fuels - are the main cause of warming since the 1950s.
That is up from at least 90 percent in the last report in 2007, 66 percent in 2001, and just over 50 in 1995, steadily squeezing out the arguments by a small minority of scientists that natural variations in the climate might be to blame.
I have three quick reactions to this
- The IPCC has always adopted words like "main cause" or "substantial cause." They have not even had enough certainly to use the word "majority cause" -- they want to keep it looser than that. If man causes 30% and every other cause is at 10% or less, is man the main cause? No one knows. So that is how we get to the absurd situation where folks are trumpeting being 95% confident in a statement that is purposely vaguely worded -- so vague that the vast majority of people who sign it would likely disagree with one another on exactly what they have agreed to.
- The entirety of the post-1950 temperature rise occurred between 1978 and 1998 (see below a chart based on the Hadley CRUT4 database, the same one used by the IPCC
Note that temperatures fell from 1945 to about 1975, and have been flat from about 1998 to 2013. This is not some hidden fact - it was the very fact that the warming slope was so steep in the short period from 1978-1998 that contributed to the alarm. The current 15 years with no warming was not predicted and remains unexplained (at least in the context of the assumption of high temperature sensitivities to CO2). The IPCC is in a quandary here, because they can't just say that natural variation counter-acted warming for 15 years, because this would imply a magnitude to natural variability that might have explained the 20 year rise from 1978-1998 as easily as it might explain the warming hiatus over the last 15 years (or in the 30 years preceding 1978).
- This lead statement by the IPCC continues to be one of the great bait and switches of all time. Most leading skeptics (excluding those of the talk show host or politician variety) accept that CO2 is a greenhouse gas and is contributing to some warming of the Earth. This statement by the IPCC says nothing about the real issue, which is what is the future sensitivity of the Earth's temperatures to rising CO2 - is it high, driven by large positive feedbacks, or more modest, driven by zero to negative feedbacks. Skeptics don't disagree that man has cause some warming, but believe that future warming forecasts are exaggerated and that the negative effects of warming (e.g. tornadoes, fires, hurricanes) are grossly exaggerated.
Its OK not to know something -- in fact, that is an important part of scientific detachment, to admit what one does not know. But what the hell does being 95% confident in a vague statement mean? Choose which of these is science:
- Masses are attracted to each other in proportion to the product of their masses and inversely proportional to the square of their distance of separation.
- We are 95% certain that gravity is the main cause of my papers remaining on my desk