Page last updated at 12:14 GMT, Friday, 28 August 2009 13:14 UK

Sunspots linked to Pacific rain

By Sudeep Chand
Science and environment reporter, BBC News

Sunspots (KVA/Thomas Berger/LMSAL)
More spots are associated with increased solar activity

A study has shown how sunspots could affect climate in the Pacific.

Writing in the journal Science, the international team detailed how the 11-year sunspot cycle might influence the amount of rain falling on the ocean.

It is hoped the findings will lead to better models for regional climate predictions.

The authors emphasised the findings "cannot be used to explain recent global warming because of the trend over the past 30 years".

Sunspots are cooler areas on the Sun's surface that are marked by intense magnetic activity.

Although dimmer than their surroundings, their presence is usually accompanied by bright spots, or faculae, which result in a slight general overall brightening of our star when it is most active.

Sunspots and rain

The new study suggests that relatively small variations in sunspot activity might result in changes in climate.

Two mechanisms are involved.

The first is "top-down" where changes in the upper layers of the atmosphere contribute to wetter conditions below.

The second is "bottom-up" where the ocean evaporates and more clouds are produced.

The study used models to show how these two mechanisms might act together to produce rainfall similar to that observed in the tropics.

In addition, the models predict a cooling effect of the surface of the ocean in equatorial regions.

A step forward

Brad Carter, from the University of Southern Queensland, Australia, said: "This paper represents a useful step forward."

Others, however, were not so convinced.

In an interview with the journal Science, Joanna Haigh from Imperial College London, UK, said: "It is not nearly as conclusive as they would have it."

In the same interview, David Rind of the US space agency (Nasa) added that "even if the amplifier exists, its climate leverage is still relatively puny".

In response Dr Meehl, one of the authors of the study, told BBC News: "There could be other mechanisms in the system that also connect solar variability to climate.

"But the new result here is that we have identified these two (mechanisms) that can produce signals of the size we expect to see in the observations.

"And we've reproduced them in a climate model simulation for the first time."

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