Figuratively warming

Roy Turnbull and Guthrie Stewart dispute details of the figures I cite on global warming (Letters, 27 December).

This is to miss the point, which is the roughness of the underlying calculation. According to the International Panel on Climate Change's report, our effect on how much solar radiation the Earth retains is small (about 0.5 per cent) and uncertain (that figure -60 per cent, +50 per cent). The biggest factor in this uncertainty is our poor understanding of aerosols and clouds. The uncertainty is itself uncertain, no more than a guess at how little we know.

Perhaps man is causing global warming. Al Gore's evangelical zeal suggests it is Gospel truth, but since when did Gospels quote estimates of their own uncertainty? Data from ice cores show that rises in atmospheric have often come after rises in temperature, not before.

This illustrates that other factors besides greenhouse gases can raise the Earth's temperature (and by more). Our understanding of what warms us out of ice ages is weak. Add all our ignorance up: is it heresy to ask whether we are certain this is our fault?

Luckily, the greenly orthodox are unlikely to burn heretics. That would only release yet more .

MARK BAKER

Comely Bank Avenue

Edinburgh