Tuesday, May 10, 2011

preliminary attribution

We expect to be away and unplugged for about three months, and I wish everyone a happy and safe summer.  Before signing off, I would like to close the sequence of posts in this academic year with some questions about attribution.

Attribution is the soft underbelly of global warming.  It is where deniers and skeptics strike rational blows below the belt.  Climate change is an ever more tangible reality, but time and again we hear that freak weather cannot be firmly linked to climate climate, making it intangible again.  This puts us in a strange spot.  On the one hand, we know climate change can inform weather events.  On the other, weather events cannot be attributed rigorously to climate change.

When something comes into being we expect, on some level or another, to be able to touch it.  If we cannot touch it, we would find it reasonable to doubt its being.  A changing climate has meteorological consequences, but freak weather may also be due to other causes.  Obviously, freak weather events happened already before the industrial revolution that eventually sparked climate change.

That's baby logic: if p is climate change, and q is freak weather, and we know p implies q, and we also know p happens, then q follows.  But from p implying q, and from us affirming the consequent q, does not follow p.  Inferring climate change from freak weather, or attributing freak weather to climate change, is a logical fallacy.

So far so frustrating.  But there is a way out.  Here is how.  Let us think of attribution in terms of tangibility, and of tangibility in terms of proportion.  Remember the 1998 Roland Emmerich movie Godzilla?  Rather lousy, I admit, but the advertisement was cool: size does matter

A giant putting down a foot cannot squash microbes.  Conventional wisdom tells us that climate change is just too big to squash local weather into a new shape, even if common sense suggests the opposite.  Climate refers to a long-term meteorological average in a spacetime field; weather expresses momentary conditions at a point.  Climate and weather relate to one another like an oscillation and an interval, a melody and a note, or Godzilla and the bug.

While there are difficulties attributing a tiny effect to a giant cause, the difficulties lessen as soon as we fiddle with magnification.  On the smallest, microbial level, I can certainly not attribute the heat and humidity (33 C, 90 %) of today's bicycle commute from home to campus to global climate change.  After all, this is south Florida; it's mid-May; it hasn't rained in a while, and thunderheads are building up.  So what do you expect?  On the other extreme, at the largest, planetary level, I certainly can attribute, say, the Arctic melt to climate change, if only because of the hugeness of the effect and the consequent proportionality of causation.  Here cause and effect are of comparable size.  Moreover, here certainty runs so high that it would be silly to object.  For illustration, think of G. Monbiot's four questions in Heat 2007: 1. does the atmosphere contain CO2?  2. does atmospheric CO2 raise the average global temperature?  3. Will this influence be enhanced adding more CO2?  4. Have human activities led to a net emission of CO2?  Since we are forced to answer yes, yes, yes, and verily, yes, to the questions, the dwindling North Polar ice cover is an attributed consequence of the 'duh!' variety.  This is the epistemic comfort zone.

The query then becomes: how small does attribution get? Or: how far can we push cause and effect out of proportion to attribute the latter still to the former?  One line of inquiry concerns mid-size events such as the Arctic Blowout and the consequent harsh winters in Florida (more findings here).  Other examples of medium-scale attribution are the relation of global climate change to Himalayan warming and to worsening allergies in North America.  Other inquiries concern not-quite-long-term processes, e.g. the relation of global climate change in the past thirty years to a five percent reduction in world crops such as wheat and maize.  All this is certain in being measurable, explainable, and peer-reviewed to boot. 

Can we make it smaller? Here recent work examines the deepening aridification of Mexico, the inundation increase of the Mekong delta in Vietnam, the harsher weather swings in Mozambique, last year's floods in Pakistan, last year's fires in Russia, and the American snowmaggedon.  (Specific links are in the 'attribution' file here.)  This type of research has drawn various criticisms; so the connections are arguable but not all that sure yet.  Well, then, let's wait.  My guess is that it is only a question of time before these causal connections will harden.

Lest we forget, there is also a pragmatic way out of this puzzle.  Should we remain unpersuaded by the subtle etiology of freak weather, then perhaps it were wise to pay attention to the analysts at reinsurers such as Munich Re.  They went on record with declaring that "the only plausible explanation for the rise in weather-related catastrophes is climate change."

When information is still soft, and when it's your investment that's at risk, prudence points the way. 

Have a nice summer.

Sixty-seven months left.

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