William writes:
The main points that most would agree on as "the consensus" are:
1. The earth is getting warmer (0.6 +/- 0.2 oC in the past century; 0.1 0.17 oC/decade over the last 30 years (see update)) [ch 2]
2. People are causing this [ch 12] (see update)
3. If GHG emissions continue, the warming will continue and indeed accelerate [ch 9]
4. (This will be a problem and we ought to do something about it)
I've put those four points in rough order of certainty. The last one is in brackets because whilst many would agree, many others (who agree with 1-3) would not, at least without qualification. It's probably not a part of the core consensus in the way 1-3 are.
Yep, all of that remains pretty well true, and remains the core....In the years since I wrote that nothing has come along to overturn any of that, and much has come in to buttress it....However, I still think there is room for honest skepticism and disagreement about point 4.... The real argument should be about point 4: that it will be a problem and we should do something about it....I don't know the answer to point 4, and I know that I don't know :-).
So let's stop there for a moment. I think it's better to split point 4 into:
4.a. This will be a problem.
4.b. (We ought do something about it).
I don't think it's reasonable for anyone to acknowledge point 3, especially acceleration, and deny 4.a. Even in the imaginary world where benefits in some areas outweigh the problems in others, there are still problems. And virtually no one really believes in that imaginary world - if we could wave a Pielkean magic wand, a technology that cheaply and safely scrubs all GHG emissions from the atmosphere, any reasonable person given a yes or no choice on waving that wand would do it.
As for 4.b., I'll just note that it's not an exclusively scientific question - engineers, economists, and wonderful wonderful lawyers all play a part, not to mention the general public that pays the bill one way or another. No wonder it's a squishier issue.
Also on 4.b., I think if we drop two unstated assumptions in much of the climate discussion - first, that the universe ends in the year 2100, and second, new GHG emissions will magically cease the moment we hit 2x present CO2 equivalent levels - then we know the answer. Maybe someone could argue we still have a decade or so of playtime available before doing something about the problem but that would both be unwise and not relevant to 4.b.
Finally, I may not know anything more about ocean acidification than William notes in original post (probably less), but it's really a separate scientific consensus issue that doesn't even depend on climate change being real. My amateur opinion is that acidification consensus is as solid as the climate consensus through its own version of 4.a., and on policy matters the issue pushes for the same policy solutions as climate change other than some geoengineering and ocean sequestration proposals, and possibly on a slightly longer timeframe.
UPDATE: I continue to think, without much evidence to back it up, that the biggest human cost from GHGs will be malnutritrion-related deaths in areas of subsistence agriculture and fishing due to precipitation shifts and acidification. Not necessarily an increase against the present baseline but an increase against a future baseline where the world aggressively reduces GHGs.
UPDATE: I continue to think, without much evidence to back it up, that the biggest human cost from GHGs will be malnutritrion-related deaths in areas of subsistence agriculture and fishing due to precipitation shifts and acidification. Not necessarily an increase against the present baseline but an increase against a future baseline where the world aggressively reduces GHGs.
