The big skies painted by Norfolk's foremost artist have long been admired by art lovers.But though John Crome's tranquil Broads scenes have changed hands for thousands of pounds, few have ever have imagined that they would find a use in climate research.

By SARAH BREALEY

The big skies painted by Norfolk's foremost artist have long been admired by art lovers.

But though John Crome's tranquil Broads scenes have changed hands for thousands of pounds, few have ever have imagined that they would find a use in climate research. Now scientists from the National Observatory of Athens have studied three of Crome's paintings: Windmill Near Norwich; Yarmouth Harbour - Evening; and Moonrise on the Yare, to discover the effects of volcanic eruptions on the climate.

There were, of course, no volcanic eruptions in Norfolk, but major eruptions have an effect stretching across thousands of miles and up to three years. They leave aerosol particles in the air, which block out sunlight and can even lead to the earth cooling. The eruption of Mount Tambora in Indonesia in 1815 led to the "year without a summer" in 1816, in which crops failed in North America and northern Europe. Thousands died of starvation, there were food riots in England and red snow fell all year in Italy. Sunsets were also unusually spectacular.

It was for this reason that the Greek scientists looked at 311 paintings of sunsets between 1500 and 1900. They measured the red-green ratio in each to work out how striking the sunsets were. Of those, 54 paintings by 19 artists - including Crome, the founder of the Norwich School of painting - were produced after a major eruption, while the rest were used to measure normal atmospheric conditions.

Christos Zeferos, who led the research, said: "In this period the only other observational measurements we have are descriptions, which are subjective estimates of what the observer is describing. We have tried to get an objective estimate using art, which has never been done before."

But surely artistic licence makes it dangerous to measure anything too closely from a painting? The scientists say they were surprised by how accurate the painters were. The study, published in the journal Atmospheric Chemistry and Physics, says that there was a strong correlation between the level of red in the sunsets painted and existing measurements of volcanic particles over time - an index developed by former UEA scientist Hubert Lamb.

It adds that the works of famous painters contain important information, even though most of them would have had no idea about the eruptions whose effects they were painting.

The difference can be seen most clearly in two Turner paintings. The Lake, Petworth, Sunset, painted in 1828, is what the scientists call "an example of a non-volcanic sunset", with a clear blue sky streaked with orange.

Sunset, painted in 1833, is a dramatic red and orange sky, showing the effects of a Philippines eruption in 1831.

Crome's Yarmouth Harbour - Evening shows boats clustered together, almost silhouetted against an orange sunset sky. Windmill near Norwich is more muted, with Trowse post mill silhouetted against a darkening orange glow.

Both are held by the Tate and were painted in 1816, when the effects of the Tambora eruption would have been visible.

Prof Zeferos said: "If you measure the ratio of red to green [in the Crome paintings] you can say yes, there is something unusual in the atmosphere and this unusual thing was caused by aerosol debris in the atmosphere."

He added: "I hope it will improve our knowledge of past climates, because we rely on our knowledge of the past to forecast future changes."

The scientists are now using their research to see if the data which the Inter-Governmental Panel on Climate Change is using for its climate change predictions is accurate. They are also planning a study of 20th-century paintings and whether they show the effect of pollution on sunsets.