Health hazard

Imagine a Britain where malaria could be a hazard of a trip to the coast, where new as well as old diseases are spread by swollen populations of rats and ticks, and where thousands die of heat stroke in the summer. This is no science-fiction scenario: it's the prediction of experts monitoring climate change.

Global warming has direct consequences for human health. We have already had intimations of what may be in store. The biggest wake-up call came two years ago, when a heatwave killed 15,000 people in northern France and about 2,000 in England and Wales.

But strangely, the net impact of year-round warmer weather may not be disastrous. More lives may be saved in the winter in Britain than are lost in the summer. An expert group set up by the Department of Health in 1999 produced a report in 2002 on the likely impact of climate change on health up to the 2080s.

The UK has the highest death rate in winter in Europe, they said, with about 60,000 to 80,000 cold-related deaths. By 2050 - assuming the UK enjoys increasingly warmer, if wetter, winters - they estimate that excess cold weather deaths will have dropped by as much as 20,000 a year, if nothing else changes. The increase in deaths related to the heat will be much less, between 800 and 2,800 a year. Most of those who die in heatwaves are those with health problems, the very old and the very young. According to the Hadley Centre, a part of the Met Office that models climate change, we cope fairly well with hot days, as long as the temperature drops before bedtime.

"There is trouble if it does not cool down at night," said Richard Betts, who leads the research group. "The key temperature is 18C. If it doesn't drop below, that starts to have a distressing effect on the body." Since 2003, the Met Office has advised the NHS on likely hot spells so it can prepare for increased hospital admissions and primary care trusts can warn the vulnerable.

But climate change will bring other problems, such as more cases of food poisoning, says the expert committee. They predict 10,000 more cases a year by 2050. Hot weather helps bacteria to breed, so care over food storage, preparation and hygiene will become increasingly important.

Malaria will come back to Britain by 2050, they predict, but not the most dangerous kind. Malaria was a leading cause of death in the salt marsh communities between the 16th and 19th centuries. Vivax malaria - not the most lethal falciparum variety of much hotter places - was found in the Fens, the Thames estuary, south-east Kent, the Somerset Levels, the Holderness of Yorkshire and the coastal districts of the Firth of Forth.

Drainage schemes in areas where mosquitoes bred, better housing conditions and improvements in medical treatment put an end to malaria in the UK. After people stopped becoming ill with malaria, the mosquitoes, which transmit infection, became harmless - but five species capable of transmitting vivax malaria remain in Britain.

At the moment, it is only warm enough for transmission during a few months in the south of England. Hotter summers would extend that window of opportunity and people who spent more time out of doors in the evening or left their windows open at night would be at greater risk of getting bitten. If malaria is re-introduced from abroad, an epidemic is possible.

Public health officials are also monitoring for West Nile fever, which is transmitted by mosquitoes. Tick-borne diseases are also climate-sensitive and could increase, as could Lyme disease.

Waterborne diseases become more problematic in hotter climates, but cholera and typhoid are unlikely to return because of Britain's good sanitation.

There is concern about the increase in UV radiation through depletion of the ozone layer. If that continues, and summers become hotter and sunnier, there will be more cases of skin cancer unless people stay out of the sun. The Department of Health report estimated an extra 5,000 cases of skin cancer and 2,000 of cataracts every year by 2050.