Monday, 3 January 2011

The weather this winter

This winter has been unseasonably early and cold, both in Northern Europe and the US.

It has been known for some time that volcanic eruptions can alter the climate in the short-term - for instance the Mount Pinatubo eruption in 1991 is credited as having affected the global temperature the following winter.

The 1815 Tambora eruption is said to have reduced global temperatures by three degrees Celsius, and to have caused the 'year without a summer'. The same happened after the 1883 eruption of Krakatoa, after which global temperatures decreased by 1.2 degrees, an effect that lasted for several years.

The atmospheric effects of these explosions were seen in the form of vivid sunsets all over the world. Edvard Munch's 'The Scream' possibly shows the skies seen over Norway after the Krakatoa explosion. Likewise, Turner's painting 'Chichester Canal' might have been influenced by the skies after the Tambora explosion.

So global temperature can be decreased by the type of eruption, and the effects can last for many years. So would anyone bet against the unseasonable weather having been acerbated by the eruption of the Icelandic Eyjafjallajokull volcano in April and May this year? Did it throw enough dust into the high atmosphere to cause this cold weather?

Wikipedia says it threw out 250 million tons of tephra. In comparison, Krakatoa threw out an estimated 20 cubic kilometres of tephra. Although tons and kilometres are not readily interchangeable, it is obvious that Krakatoa's eruption was several orders of magnitude larger. (*) However, was Eyjafjallajokull's eruption large enough to cause our current weather? 

Perhaps this is a connection too far, and I am most certainly not a climatologist. Cause and effect are always hard to discern in complex systems like the climate, even after the event. But I would not bet against the eruption having had some effect.

(*) Some non-reliable websites have the amount of tephra thrown out by Eyjafjallajokull as about 140 million cubic metres (0.14 cubic kilometres, or less than 1% of the mass thrown out by Krakatoa). If this is correct, then it was a much smaller eruption. Of course, not all of the tephra would have got into the atmosphere.

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