Uncertain about uncertainty
"If anyone tries to tell you that uncertainty about climate change is a reason for inaction, he’s either a fool or a scoundrel," writes Mark Kleiman. "Probably a bit of both." He explains:
Assume some climate model predicts that, under some set of assumptions, average global temperature would rise 3° C by 2100. If the model were very accurate and precise, that might be 3°± 1°. If the mechanisms involved remain obscure and the data unclear – as is the case today – that might be 3°± 5°: that is, the best guess would be a 3° increase, but the actual outcomes might range between an 8° increase and a 2° decrease.
Given how bad a 3° increase would likely be, if we knew for sure that would be the outcome in the face of inaction there would be a strong agument for making big and expensive policy changes to prevent it from happening. And if we knew that for sure, it would be very hard politically to argue against doing something about the problem.
By contrast, 3°± 5° means that proponents of inaction get to say “We’re not even sure there’s any problem at all.” That makes the political case for action much weaker. But it makes the logical case for action much stronger.
The world – especially the much richer world of our great-great-grandchildren in 2100 – could adjust to a 3°, or even a 4°, increase in global average temperature, though at great cost in species extinctions, land area lost to rising sea levels (and therefore the forced migration of some large populations), and more extreme weather. That hotter planet would be, on average, a less pleasant place to live. But it would still be habitable.
But an 8° C average temperature increase is a completely different proposition.
Opponents of climate change have been immeasurably aided by innumeracy and a studied vagueness. Most people think that the "uncertainty" in climate change is uncertainty about climate change. In reality, it's uncertainty about the extent of climate change, and it swings up as well as down. Skeptics have argued that what's relevant about the model is that earth might warm somewhat less than we think. But given that we've only got one planet, what's relevant about that model is that the earth might warm much more than we think.
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