Saturday, July 14, 2012

Turning out nice?

Since the industrial revolution our burning of fossil fuels, coal, oil and gas, has increased the concentration of carbon dioxide in the air from below 300 parts per million to about 400 ppm.  The physics that was worked out in the 19th century tells us that an increase in global temperatures is the inevitable result.  So far global average surface temperatures have increased by just under 1° C.

Surface temperatures have not increased evenly; the warming has been much greater in the Arctic than at lower latitudes.  Our weather is strongly affected by the strong high level winds, the jet stream.  The position and strength of the jet stream determines whether rain producing depressions pass over southern England or northern Scotland or are blocked from reaching us.

As the Arctic warms we get a lower temperature gradient between the Equator and the Pole.  This results in a tendency for the jet stream to be weaker and more meandering, and this in turn tends to block weather systems.  The result is longer periods of continuous wet weather or continuous fine weather; more floods and more droughts.

The frequency of such extremes has increased in recent years, right across the northern hemisphere.  It’s just what we expected.