Over at the Examiner, Thomas Fuller had a post outlining a ‘new generation of skeptical arguments against the theory of anthropogenic global warming’ (AGW), which he felt had a lot of merit. I got to his post via a comment thread at RealClimate, where he asked for input. He did get quite a lot of feedback, but unfortunately, a lot of it was packaged in a rather negative tone. (I’ll come back to communication strategies in another post.) Since he appeared to be sincerely interested, I felt compelled to react. I responded to (his framing of) his questions as follows:
You frame your questions/topics as “skeptical arguments advanced against the theory of anthropogenic global warming”. You also acknowledge that scientists are getting frustrated “answering the same ‘primitive’ objections repeatedly, only to see them resurface shortly thereafter, something that I am sure is frustrating.” I think a logical consequence is that your framing of the topic arouses a defensive reaction from climate scientists and their supporters. Based on you being aware of the scientists’ frustration in this matter, your choice of framing is rather odd, and so is your surprise about the reactions you received at RealClimate (mostly from commenters by the way; not from the RC editors). In between the snark, you did get some feedback there as to the contents of your questions/topics. It’s your choice whether to focus attention on the former (the snark) or the latter (the feedback to the content).
Most points on your list are neither new nor a threat to the theory of anthropogenic global warming. That said, some of your points have some validity in that the related uncertainties are large. Reframing your questions as “which areas in climate science have the greatest uncertainties?”, opens the door to a more constructive discussion.
A quick glance at the points your raise:
Data gathering and analysis. Points 1-4 are pretty meaningless for reasons explained at length elsewhere. The revised ocean heat content data (nr 5) don’t show a decrease of ocean heat content AFAIK, and moreover, trends have to be decided upon at appropriately long timescales. I’m not familiar enough with Tropical troposphere trends to comment on, though Santer et al (2008) found no discrepancy between modeled and measured tropical tropospheric temperatures.
Climate sensitivity and feedbacks. There is considerable uncertainty in the precise value of climate sensitivity, so in my newly proposed frame, this would be a valid point. However, taking all constraints on climate sensitivity into account, it seems very unlikely that it is far outside the boundaries you quote: 1.5 to 4.5 degrees for a doubling of CO2. The chance for all previous work to be shown totally wrong by one new piece of work is perhaps not nil, but it definitely is very small.
Plateau in current temperatures. Trends have to be decided upon at appropriately long timescales. The apparent plateau is close to meaningless for deciding on climatic trends. This truly is an old classic that gets scientifically minded persons’ defenses up.
Tipping points. The exact nature and especially timing of tipping points is extremely uncertain, so yes, this is an area where the existing knowledge is very limited. However, the limited knowledge we do have (mainly based on paleoclimate) points to the existence of tipping points, eg related to the amount of ice cover. The policy relevance may be limited to “If it’s bad, it’s really bad. If it’s good, it’s still pretty bad”.
Other climate forcings. No news there. Those other forcings are taken into account and indeed, they are additive to the changes from GHG emissions. They do not negate the radiative properties of those greenhouse gases however. Also keep in mind that many of the stronger feedbacks respond to temperature, so the amplification (or dampening) of the temperature response does not differ greatly between different forcings. That means that there is not a huge amount of wiggle room to decrease (or increase) the importance of the role of greenhouse gases (at least not without violating basic physics).
I would add one more point: Aerosols. The uncertainty surrounding them and their impact on climate change is very large. But again, don’t expect a landslide change in current wisdom just because of that. That would be wishful thinking.
It is good to keep in mind that uncertainty is not the same as knowing nothing, and that uncertainty can go both ways: for the better or for the worse. We’ll have to make decisions in the face of uncertainty, whether we like it or not. Climate policy should be about rational risk assessment, based on solid science.