Sunday, November 15, 2009

Weather, Climate and Global Warming

In my most recent blog I made mention of the common fallacy of drawing conclusions about the reality of global climate change from observations of local weather. Climate change denialists like to bring up the cold, wet summer or an unusually heavy snowfall during winter as evidence against global warming. But, as I pointed out, weather and climate must be understood differently. Weather is highly changeable on a day-to-day basis. Climate can also vary, but it does so on much longer time scales. It is quite possible that in a given year some large scale measure of climate, such as hurricane intensity, or rainfall over a large area, will move in opposition to a longer scale trend. But for the most part, changes occurring over a period of time such as a year will tend to show behavior that follows the long term trends.

I was therefore pleased to see the piece in this Sunday’s New York Times by Andrew Revkin that deals with the trends in record high and low temperatures across the United States over recent time. The data illustrate nicely that while record highs and lows continue to occur, the number of record high temperatures is increasing year by year, whereas the number of record lows is decreasing. The video in the piece, by Gerald Meehl, provides a nice explanation of what is going on.

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