Sir, – Eoin McMahon (November 23rd), who denies the IPCC’s view of global warming is mistaken in thinking that increased solar activity can contribute to it.
The variation of solar thermal radiation over a solar cycle is less than one part in a thousand and leads to a change in global temperature of only a twentieth of a degree Celsius. On the other hand, it is now recognised that variations in solar UV flux amounting to 8 per cent can cause a redistribution of energy in the northern hemisphere. According to Prof Mike Lockwood of Reading University, low UV flux causes the jet stream to move northwards and block the prevailing Atlantic westerlies. This was the situation at solar minimum in 2009-2010 when blocking high pressure systems caused two very cold winters.
The UK Met Office map of global temperature anomalies for December 2010 shows a band of cold weather stretching from Alaska to the eastern US and from northern Europe to Siberia. It also shows warming in North East Canada, Greenland, South East Europe and North East Russia. Thus the sun redistributes the energy with some regions being colder than usual and other regions being warmer. These regional temperature variations are superimposed on the relentless rise in global warming caused by greenhouse gases in our atmosphere. – Yours, etc,