29 JUNE 2002, Page 32

Blowing hot and cold

From Dr Wilson Flood Sir: In his excellent article debating the likelihood of global cooling, Andrew Kenny ('Prepare for the big chill', 22 June) stated that we do not know what has caused the regular pattern of ice ages. This is not true. It is accepted that the ice ages and the interglacials were and are probably caused by Milankovich cycles, named after Milutin Milankovich, a Serbian astrophysicist who worked on the problem in the early part of the 20th century.

The cycles arise as a result of the Earth's orbit being elliptical and the fact that the Earth precesses and wobbles rather as a top spins. This in turn causes the amount of incident sunlight to vary considerably over long periods of time. A graph of the calculated northern hemisphere solar energy over the last 150,000 years compared with the temperatures estimated from Antarctic ice cores shows a match which is quite staggering, and worrying, for the solar energy graph has been dropping of late and will continue to do so. We can know this because we are dealing with astronomical parameters which are predictable. The one unknown factor in the equation is the actual solar irradiance itself, which cannot be predicted with any great accuracy. Latest predictions are for a cold year around 2007 and a really cold spell starting in 2027. The high temperatures of the 1990s may not be seen again in our lifetimes, since they were caused by a peak in solar output which is now passing.

Predictions of global warming arising from greenhouse gases constitute a disgraceful misuse of data for political ends and divert us from more pressing issues. such as population stabilisation, environmental degradation, and political instability.

Wilson Flood

Dumfries