27 February 2011

The Flip Side of Extreme Event Attribution

I first noticed an interesting argument related to climate change in President Bill Clinton's 2000 State of the Union Address:
If we fail to reduce the emission of greenhouse gases, deadly heat waves and droughts will become more frequent, coastal areas will flood, and economies will be disrupted. That is going to happen, unless we act.
Taken literally, the sentences are not wrong. But they are misleading. Consider that the exact opposite of the sentences is also not wrong:
If we reduce the emission of greenhouse gases, deadly heat waves and droughts will become more frequent, coastal areas will flood, and economies will be disrupted. That is going to happen, if we act.
The reason why both the sentence and its opposite are not wrong is that deadly and economically disruptive disasters will occur and be more frequent independent of action on greenhouse gas emissions. If the sentences are read to imply a causal relationship between action on greenhouse gases and the effects on the impacts of extreme events -- and you believe that such a direct causal relationship exists -- the sentences are still misleading, because they include no sense of time perspective. Even if you believe in such a tight coupling between emissions and extremes, the effect of emissions reductions on extreme events won't be detectable in your lifetime, and probably for much longer than that.

Why do I bring up President Clinton's 2000 State of the Union in 2011?  Because I have seen this slippery and misleading formulation occur repeatedly in recent weeks as the issue of carbon dioxide and extreme events has hotted up.  Consider the following examples.

First John Holdren, science advisor to President Obama:
People are seeing the impact of climate change around them in extraordinary patterns of floods and droughts, wildfires, heatwaves and powerful storms.
He also says:
[T]he climate is changing and that humans are responsible for a substantial part of that - and that these changes are doing harm and will continue to do more harm unless we start to reduce our emissions
It would easy to get the impression from such a sentence that if we "start to reduce our emissions" then climate changes will no longer be "doing harm and continue to do more harm"  (or more generously, will be "doing less harm"). Such an argument is at best sloppy -- particularly for a science advisor -- but also pretty misleading

Second, Ross Garnaut, a climate change advisor to the Australian government:
[T]he systematic, intellectual work of people who've spent their lifetimes studying these things shows that a warmer climate does lead to intensification of these sorts of extreme climatic events that we've seen in Queensland, and I think that people are wishing to avoid those awful challenge in Queensland will be amongst the people supporting effective action on climate change.
It would be easy to get the impression that Garnaut is suggesting to current Queensland residents that future Queensland floods and/or tropical cyclones might be avoided by supporting "effective action on climate change."  If so, then the argument is highly misleading.

It is just logical that one cannot make the claim that action on climate change will influence future extreme events without first being able to claim that greenhouse gas emissions have a discernible influence on those extremes. This probably helps to explain why there is such a push to classify the attribution issue as settled. But this is just piling on one bad argument on top of another.

Even if you believe that attribution has been achieved, these are bad arguments for the simple fact that detecting the effects on the global climate system of emissions reductions would take many, many (many!) decades.  For instance, for an aggressive climate policy that would stabilize carbon dioxide at 450 ppm, detecting a change in average global temperatures would necessarily occur in the second half of this century.  Detection of changes in extreme events would take even longer.

To suggest that action on greenhouse gas emissions is a mechanism for modulating the impacts of extreme events remains a highly misleading argument.  There are better justifications for action on carbon dioxide that do not depend on contorting the state of the science.

3 comments:

  1. Worse storms?
    More rain?

    Ahhhh that's nothing, mere politician's same old fear mongering they use to get elected.

    I was hit by a piece of falling sky this morning.

    Now that's a serious problem.

    Maybe the UN should start up an international investigation to save the planet from the sky falling down.

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  2. I understand your point. But, is this even true:

    [T]he systematic, intellectual work of people who've spent their lifetimes studying these things shows that a warmer climate does lead to intensification of these sorts of extreme climatic events

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  3. Holdren's quote shows the President's science adviser making a demonstrably untrue statement. That bodes poorly for good policy. But what is to be expected from an acolyte of Paul Ehrlich?
    Garnaut, likewise, is making untrue assertions that will inevitably lead to bad policy.
    This is too bad for stakeholders hoping for honest policy that is effective.

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