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Tuesday, August 17, 2010

Tamino's Open Mind: "Red Hot" -- The Russian Heat Wave of August 2010

Tamino's Open Mind:  "Red Hot" -- The Russian Heat Wave of August 2010

Red Hot

This summer in Moscow the weather has been more than just unpleasant. It’s been dangerous. Not only has Moscow suffered through its worst heat wave ever, the heat has dried out forests and peat bogs in surrounding areas, leading to extensive wildfires which have filled the air with smoke. This has made the air in the city of 10,000,000 unhealthy to breathe; citizens are advised to stay indoors and keep their windows closed. Ordinarily, in such oppressive heat that suggestion would be a bad joke — but with air pollution at such dangerous levels it is, unfortunately, sound advice.

Many have suggested that the recent spate of extreme weather events, including the Russian heat wave, Pakistani floods, flooding and landslides in China, are exactly those events that become more likely due to man-made global warming. As Gavin Schmidt at the Goddard Institute of Space Studies has said, it’s better to think in terms of odds: warming might double the chances for a heat wave, for example.

It has also been suggested that the extremity and frequency of recent events is more than could be considered plausible, without humanity’s influence on climate. I decided to look at the temperature in Moscow, both in the past and at present, to estimate just how extreme the present heat wave really is. Daily data since just prior to 1950, and for a few scattered years prior to that, are available from both ECA and NCDC. Both sources supply daily high temperature data for Moscow, but the NCDC data are more up-to-date (they’re updated daily) so let’s see what they have to say.

July is Moscow’s hottest month, so it’s no surprise this year’s heat wave would occur in July (although the heat wave is still in progress). Here’s the monthly average of daily high temperature, for each July in the record which has reports for at least 20 days of the month (most of them have reports for all 31 days, and from 1960 onward no month is missing more than one day’s data):

Clearly, this July has been significantly hotter than previous years in the record.  

In fact the average daily high temperature for July 2010 is 3.6 standard deviations above the mean of all recorded July values.

For a normally distributed random variable, the chance of being so extreme is only 0.0003 — less than 1 chance in 3,000. Which agrees with statements from Russian meteorological officials that such a heat wave hasn’t been experienced in Moscow in at least 1,000 years.

And that means that the suggestion that this heat wave is just a natural variation, not due to global warming, is implausible. Or as we say here in Maine, t’aint likely.


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