By Dr. Roy Spencer

Climate science took another step backward last week as a new study from the Massachusetts Institute of Technology was announced which claims global warming by 2100 will probably be twice as bad as the United Nations Intergovernmental Panel on Climate Change (IPCC) has predicted.  The research team examined a range of possible climate scenarios which combined various estimates of the sensitivity of the climate system with a range of possible policy decisions to reduce greenhouse gas emissions which (presumably) cause global warming. Without policy action, the group’s model runs “indicate a median probability of surface warming of 5.2 degrees Celsius by 2100, with a 90% probability range of 3.5 to 7.4 degrees”.

Since that average rate of warming (about 0.5 deg. C per decade) is at least 2 times the observed rate of global-average surface temperature rise over the last 30 years, this would require our current spate of no warming to change into very dramatic and sustained warming in the near future. And the longer Mother Nature waits to comply with the MIT group’s demands, the more severe the warming will have to be to meet their projections.

Of course, as readers of this web site will know, the MIT results are totally dependent upon the climate sensitivity that was assumed in the climate model runs that formed the basis for their calculations. And climate modelers can get just about any level of warming they want by simply making a small change in the processes controlling climate sensitivity - especially cloud feedbacks - in those models.

So, since the sensitivity of the climate system is uncertain, these researchers followed the IPCC’s lead of using ‘statistical probability’ as a way of treating that uncertainty. But as I have mentioned before, the use of statistical probabilities in this context is inappropriate. There is a certain climate sensitivity that exists in the real climate system, and it is true that we do not know exactly what that sensitivity is. But this does not mean that our uncertainty over its sensitivity can be translated into some sort of statistical probability.

The use of statistical probabilities by the IPCC and the MIT group does two misleading things: (1) it implies scientific precision where none exists, and (2) it implies the climate system’s response to any change is a “roll of the dice”. We know what the probability of rolling a pair of sixes with dice is, since it is a random event which, when repeated a sufficient number of times, will reveal that probability (1 in 36). But in contrast to this simple example, there is instead a particular climate sensitivity that exists out there in the real climate system. The endless fascination with playing computer games to figure out that climate sensitivity, in my opinion, ends up wasting a lot of time and money.

True, there are many scientists who really do think our tinkering with the climate system through our greenhouse gas emissions is like playing Russian roulette. But the climate system tinkers with itself all the time, and the climate has managed to remain stable. There are indeed internal, chaotic fluctuations in the climate system that might appear to be random, but their effect on the whole climate system are constrained to operate within a certain range. If the climate system really was that sensitive, it would have forced itself into oblivion long ago. The MIT research group pays lip service to relying on “peer-reviewed science”, but it looks like they treat peer-reviewed scientific publications as random events, too. If 99 papers have been published which claim the climate system is VERY sensitive, but only 1 paper has been published that says the climate system is NOT very sensitive, is there then a 99-in-100 (99%) chance that the climate system is very sensitive? NO. As has happened repeatedly in all scientific disciplines, it is often a single research paper that ends up overturning what scientists thought they knew about something.

In climate research, those 99 papers typically will all make the same assumptions, which then pretty much guarantees they will end up arriving at the same conclusions. So, those 99 papers do not constitute independent pieces of evidence. Instead, they might be better described as evidence that ‘group think’ still exists. It turns out that the belief in a sensitive climate is not because of the observational evidence, but in spite of it. You can start to learn more about the evidence for low climate sensitivity (negative feedbacks) here.

As the slightly-retouched photo of the MIT research group shown above suggests, I predict that it is only a matter of time before the climate community placing all its bets on the climate models is revealed to be a very bad gamble. See full blog here.