JAMES RANDERSON— GUARDIAN NEWSPAPERS LIMITED 2007

Rainfall across U.K. has increased by 6.2 mm a decade

Most of the rise may be due to greenhouse gases

Greenhouse gas emissions from human activity are causing global shifts in rainfall patterns and contributing to wetter weather over the U.K., climate scientists said recently.

Their study is the first to find a ‘human fingerprint’ in the rainfall changes which have been detected in a belt of the northern hemisphere stretching from the Mediterranean to the U.K. to Norway.

The results, based on a global comparison of weather records going back to 1925, suggest that levels of rainfall across the UK have increased steadily by an average of 6.2 millimetres every decade. At least half of the extra rainfall and possibly up to 85 per cent is caused by the impact of greenhouse gas emissions, the scientists conclude.

The research, carried out by the Hadley Centre of the UK Meteorological (Met) Office in conjunction with several national climate research institutes, does not prove that any single episode of extreme wet weather can be directly linked to climate change, but it supports the idea of a long-term rise in rainfall linked to emissions.

The study, published recently in the journal Nature, adds weight to the growing belief that the U.K. is experiencing a fundamental shift in weather pattern with bursts of extremely hot conditions and almost tropical downpours.

In central England as waters of the Severn, Avon and Thames continue to rise, the UK Environment Agency described conditions in the region as the “worst floods in modern times.”

Flood devastation

The prime minister Gordon Brown, who flew over the flood region recently, said: “Like every advanced industrialised country, we are coming to terms with the issues surrounding climate change. “We are going to have to look at drainage, surface water, as well as river water, and what we are going to be able to do in the future in relation to that. We will have to invest in coastal defences, flood defences and, of course, drainage in infrastructure in the years to come and that’s why we are setting aside more resources to do so.”

The recent study compared records from weather stations around the world going back to 1925 with predictions from 10 computer models of global climate.

Some models included the effects of human-induced climate change while others took into account only natural changes or more exotic factors such as volcanoes and the sun’s activity.

Only models factoring in human-induced climate change could adequately explain the observed changes in rainfall, the scientists found.

“The paper is saying there is a significant human influence on global rainfall patterns,” said Dr Peter Stott at the Met Office’s Hadley Centre, who was part of a team led by researchers at the Climate Research Division of the Canadian government’s environment department.

“The study looks at the trends in annual precipitation, but we don’t address the trickier issue of what is happening with the extreme events.

Especially regionally, that is harder to discern because there is much more variability and the events are rarer as well, so it is a more difficult problem.”

Apart from the increase in rain in northern high latitudes — the belt between 40 and 70 degrees north which includes the U.K. — the analysis found that climate change brought wetter conditions in the southern tropics and subtropics.

Very important paper

It also found a link between global warming and drier conditions in the northern tropics and subtropics. “This is a very important paper,” said Myles Allen, head of the climate dynamics group at Oxford University, U.K. “We already knew that external drivers like volcanic eruptions affect large-scale precipitation, but for the first time this paper identifies the fingerprint of human influence. This means that the precipitation trends they identify may be harbingers of more to come.”

In the UK, the long-term forecast is for wetter winters and drier summers. “The really difficult one to figure out is that even under drier summers you might get more extreme events,” Dr Stott said.

Chris Huntingford a climate modeller at the Centre for Ecology and Hydrology in Wallingford, UK, said: “It has now been confirmed that the burning of fossil fuels has altered rainfall patterns at the global scale.

Dangerous change

Next we need to understand how these observed large-scale adjustments translate to local changes in extreme rainfall events.

“These highly regionalised estimates of rainfall will be essential in aiding governments to prepare for what might, in some circumstances, represent dangerous climate change.”