Sunspots linked to global warming: 18th-century climate records cast doubt on 'greenhouse effect'

SUNSPOTS, rather than 'greenhouse' gases from the burning of fossil fuels, may be responsible for the rise in global temperatures over the past 200 years, it was claimed yesterday.

Astronomers at Armagh Observatory in Northern Ireland have studied meteorological records going back to 1795, which point to a strong link between air temperatures on Earth and solar activity. Dr John Butler, who presented the results at the European and National Astronomy Meeting in Edinburgh, said: 'It looks as though carbon dioxide (the principal greenhouse gas) has not been the most dominant factor in global warming for the past 200 years.'

The new results are bound to fuel political controversy. The right- wing think-tank, the Institute of Economic Affairs, recently published a pamphlet questioning scientific predictions about a link between rising concentrations of greenhouse gases in the atmosphere and increases in global temperatures. The institute has an explicit economic agenda, urging that government should take no action to tackle climate change and in particular arguing against the introduction of carbon taxes to decrease the consumption of fossil fuels.

Dr Butler, however, said: 'Carbon dioxide may well become dominant in future.' His results reinforce claims made by two Danish meteorologists a couple of years ago who found a correlation between the length of the sunspot cycle and temperatures on Earth.

The Armagh observations contain one local irony. According to Dr Butler, they show that 'global warming has taken 10 years longer to reach Northern Ireland than Central Europe'. He puts this down to the proximity of the Atlantic Ocean and the well-known effect that the oceans take longer to heat up than the land or the air.

Sunspots are dark patches of gas that are slightly cooler than their surroundings on the surface of the Sun. They can be as small as 600 miles across or larger than 25,000 miles (about three times the diameter of the Earth). It is not the number of sunspots that affects the Earth's climate, according to Dr Butler, but the length of the sunspot cycle. This averages about 11 years, but periods when the cycle becomes shorter correspond to greater solar activity and greater energy output from the Sun.

Dr Butler pointed out that during the past 20 years, the solar cycle has been abnormally short (about 9.6 years) and the Earth's weather abnormally warm. On the other hand, a period in the late 17th century known as 'The Little Ice Age' when the Thames froze in winter, corresponded with an abnormally long solar cycle, when sunspots virtually ceased for about 60 years.

The Armagh observations are not quite the world's longest continuous series of temperature measurements. Kew has records going back to the 1770s. However, Kew's ancient records are not comparable with more recent ones becuase of the growth of London. Cities generate their own micro-climate, which is usually a degree or so warmer than the surrounding countryside. Since the population of Armagh has not mushroomed in the same way as London's during the period of the observations, there is a greater consistency in the Irish records.

According to Dr Butler, the measurements had been entered in old foolscap books '30 to 40 pages each, piled on shelves and in cupboards and things. It was only when we started cataloguing them three or four years ago that we realised what we had'.

Dr Butler wants to subject the data to computer analysis to discover, for example, whether the rise in average annual temperature reflects disproportionately warmer winters or whether summers and winters have got warmer together.