Our own observatory at Armagh is one of the oldest in the world and has been observing solar cycles for more than 200 years.

What this work has shown is that, over all of this time, short and intense cycles coincide with global warmth and long and weak cycles coincide with cooling.

Most recently, this pattern continued in the 1980s and 1990s when cycles 21 and 22 were short (less than 10 years) and intense and it was notably hot. But all this now looks set to change.

Cycle 23, which hasn't finished yet, looks like it will be long (at least 12 to 13 years) and cycle 24, which has still to start, looks like it will be exceptionally weak.

Based on the past Armagh measurements, this suggests that over the next two decades, global temperatures may fall by about 2 degrees C — that is, to a level lower than any we have seen in the last 100 years. Of course, nothing in science is certain. Perhaps (though I doubt it) Armagh's old measurements are wrong or perhaps there are now other factors, such as CO2 emissions, which may change things somewhat.

However, temperatures have already fallen by about 0.5 degrees C over the past 12 months and, if this is only the start of it, it would be a serious concern.

Northern Ireland is not noted for extreme warmth at the best of times and has much more to fear from cold weather than it does from hot. We really need to be sure what is going to happen before spending too much money on combating global warming.

We may need all the money we can save just to help us keep warm.

David Watt

Brentwood

Essex