NCPA - National Center for Policy Analysis

Extreme Weather: What Role Do Humans Play?

March 18, 2011

Tying weather extremes to global warming, or using them as "proof" that warming does not exist, is a popular rhetorical flourish by politicos of all stripes.  But a string of soon-to-be-published papers in the scientific literature finds that despite all hue and cry about global warming and recent extreme weather events, natural climate variability is to blame, says Patrick J. Michaels, a senior fellow with the Cato Institute.

  • The first chink in the armor came back in the fall of 2010, when scientists from the Physical Sciences Division of the Earth System Research Laboratory of the National Oceanic and Atmospheric Administration presented the results of their preliminary investigation.
  • They concluded that "despite this strong evidence for a warming planet, greenhouse gas forcing fails to explain the 2010 heat wave over western Russia. The natural process of atmospheric blocking, and the climate impacts induced by such blocking, are the principal cause for this heat wave."

What about the past two winters?

  • In a soon-to-be-released paper to appear in Geophysical Research Letters, a team of scientists from the European Center for Medium-Range Weather Forecasts help untangle the causes of the unusual atmospheric circulation patterns that gave rise to the harsh winter of 2009-2010 on both sides of the Atlantic.
  • They find: "neither SST [sea surface temperature] nor sea ice anomalies explain the negative phase of the NAO [North Atlantic Oscillation] during the 2009/10 winter."

The point is that natural variability can and does produce extreme events on every time scale, from days (e.g., individual storms), weeks (e.g., the Russian heat wave), and months (e.g., the winter of 2009-2010).  Folks would do well to keep this in mind next time global warming is being posited for the weather disaster du jour, says Michaels.

Source: Patrick J. Michaels, "Overplaying the Human Contribution to Recent Weather Extremes,", March 10, 2011.

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