Wednesday, April 20, 2016

This Paper Will Cause a Lot of Problems....

Nature just published a paper that isn't very surprising, but will be at least a little confusing to those who are concerned about anthropogenic global warming, and immediately and loudly exploited by "skeptics." I suspect it is going to be difficult for those concerned about AGW to counter.

"Recent improvement and projected worsening of weather in the United States," Patrick J. Egan & Megan Mullin, Nature (2016).
Here we show that in the United States from 1974 to 2013, the weather conditions experienced by the vast majority of the population improved. Using previous research on how weather affects local population growth to develop an index of people’s weather preferences, we find that 80% of Americans live in counties that are experiencing more pleasant weather than they did four decades ago. Virtually all Americans are now experiencing the much milder winters that they typically prefer, and these mild winters have not been offset by markedly more uncomfortable summers or other negative changes.
Basically this study looked at where Americans moved over this time period. This isn't a perfect proxy for weather preference, but the authors write "all published population growth models reveal the same preference structure with respect to seasonal temperatures: Americans appreciate warm winters and dislike hot, humid summers." By looking at changes in county populations (and excluding Alaska), the authors found that on average the population shifted towards a climate with a change in daily maximum January temperatures of +0.58 °C per decade, and daily maximum July temperatures rose by only
+0.07 °C per decade.

However, people often move for reasons other than weather -- notably for economic reasons, and this may be a weak point of this study: the decline in rust belt jobs and the expansion in jobs in warmer parts of the country, notably the southwest. But you could counterargue that the jobs are in "better" climates because that's where people are moving.

In any case, a little better weather -- or, at least, the perception of better weather -- comes with a problem: we can't naturally (viz. without geoengineering) stop global warming on a dime; nature's thermostat doesn't work that way. And therein lies the rub.

The abstract continues:
Climate change models predict that this trend is temporary, however, because US summers will eventually warm more than winters. Under a scenario in which greenhouse gas emissions proceed at an unabated rate (Representative Concentration Pathway 8.5), we estimate that 88% of the US public will experience weather at the end of the century that is less preferable than weather in the recent past. Our results have implications for the public’s understanding of the climate change problem, which is shaped in part by experiences with local weather. Whereas weather patterns in recent decades have served as a poor source of motivation for Americans to demand a policy response to climate change, public concern may rise once people’s everyday experiences of climate change effects start to become less pleasant.
Many people will understand that global warming doesn't stop here, but they might wonder if this result should make them do a little rethinking. But many people won't understand this on purpose, and use this to study for the cause of denial.

But the optics (as they say) of this paper are bad.

Obviously the counterpoints to it are:
  1. The US isn't the world, and just because weather has gotten better here doesn't mean it's gotten better elsewhere or everywhere.
  2. Sea level is still rising, ice is still melting, and the ocean is still acidifying. There is far more to global warming than the weather or temperature you experience. 
  3. The warming is already having consequences this study doesn't capture. It's making droughts worse. (Whether it had a hand in creating a drought nor not, global warming always makes droughts worse because it increase evaporation rates.) Extreme rainfall events are increasing. 
  4. Just you wait.
It would be interesting to know if this finding holds for other (or most) mid-latitude regions around the world, in both hemispheres.

And it will be intertesting to see how this study is covered by the media.

Added: More thoughts, and more skepticism, at my next post.

1 comment:

Layzej said...

This seems to be in line with economic assessments that find net benefits for the first 1C.