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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.

By Ezra Klein  |  December 14, 2009; 9:09 AM ET
Categories:  Climate Change  
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I tend to have a litmus test for when people are serious about global warming being a crisis. Once people are willing to seriously look at getting most of our power from nuclear then I know they are serious. Once they are ready to discuss having an across the board carbon tax that affects everyone then I know they are serious. But when even the people most concerned about global warming are not willing to go down those roads then its a whole different story.

Posted by: spotatl | December 14, 2009 9:28 AM | Report abuse

Hi Ezra,

I am sorry to say this, but you are wasting your breath here.

The folks who are against climate change are fairly similar (or maybe even the same guys?) as those who are against evolution: No amount of science will sway their minds.

This is dogma to them. They believe they are right, and will pull science out of nowhere to prove that they are right. It's been 83 years since the Scopes monkey trials, and look where we are: Only 39% of Americans believe in evolution.

It's not that evolution isn't real, just as it is not that climate change isn't real. It's that people are unwilling to believe the facts that are staring them right in the face if it's inconvenient to them. Evolution is inconvenient to religious beliefs. Climate change is inconvenient to their way of life and their wallet.

Sometimes I wonder about the capacity for survival of the human race....

Posted by: JERiv | December 14, 2009 9:45 AM | Report abuse

It's worth mentioning that 3° C = 5° F and 8° C = 14° F! That's a lot!

Posted by: willholm | December 14, 2009 9:53 AM | Report abuse

I'm with spotatl on this. When people start advocating actions that they weren't already in favor of before anybody ever heard of global warming, then we'll know it's "arrived" as a serious issue.

Posted by: tl_houston | December 14, 2009 10:00 AM | Report abuse

--"a reason for inaction"--

So, Klein, other than advocating for an abridgment of your fellow citizen's freedoms and wealth, what "action" did you take today to mitigate against the alleged effects of climate change?

Posted by: msoja | December 14, 2009 10:42 AM | Report abuse

Did academics fudge climate change data?

If that is the case, that is very bad! Especially since academics are held to high standards.

Posted by: RandomWalk1 | December 14, 2009 12:58 PM | Report abuse

To global warming denialists: please address Ezra's actual point. All your other points have been rebutted elsewhere. It gets tiresome having every climate change thread overwhelmed with ad hominem attacks on the author, conspiracy theorizing, and insinuations or assertions of bad faith on the part of the non-denialists. This isn't the way responsible grownups debate.

Posted by: dfhoughton | December 14, 2009 1:15 PM | Report abuse

GW: Blah blah blah.

Non-GW: I think there's a good chance you don't have any idea what you're talking about.

GW: Well, that's all the more reason!

Posted by: ostap666 | December 14, 2009 1:30 PM | Report abuse

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