Senior doctors today published a report warning that climate change is the biggest threat to global health of the 21st century.

Rising global temperatures would have a catastrophic effect on human health, the doctors said, and patterns of infection would change, with insect-borne diseases such as malaria and dengue fever spreading more easily.

Heatwaves such as occurred in Europe in 2003, which caused up to 70,000 "excess" deaths, will become more common, as will hurricanes, cyclones and storms, causing flooding and injuries.

"We have not just underestimated but completely neglected and ignored this issue," said Richard Horton, editor of the Lancet, which published the report commissioned from University College London. "This has not been an issue on the agenda of any professional body in health in the last 10 years in any significant way. This report is one of the stepping stones in changing that culture within the health sector. It is the biggest employer in Britain and it should be a leading voice in the debate."

The lead author of the report, Prof Anthony Costello, a paediatrician who works on maternal and newborn health in the developing world, said his own views had changed. "I thought there were other priorities 18 months ago," he said. Now he believed that mitigating the impact of rising temperatures was urgent. "Every year we delay, the costs go up. We are setting up a world for our children and grandchildren that may be extremely turbulent."

The biggest impact could be in food and water shortages, which in the past have led to war and mass migration.

Prof Hugh Montgomery, of UCL's institute for human health and performance, who was one of the report's authors, noted that Mikhael Gorbachev had linked 21 recent conflicts to water instability.

The report says that the poorest people in the world will be worst affected. Although the carbon footprint of the poorest billion people is about 3% of the world's total footprint, loss of life is expected to be 500 times greater in Africa than in the wealthy countries.

Despite improvements in health, 10 million children still die every year, more than 200 million children under five are not developing as well as they should, 800 million people are hungry, and 1,500 million people do not have clean drinking water. All those things could worsen very significantly, the report says.

The impact of heatwaves, flooding and global food shortages will be felt in Britain too, the authors warned. "This is an immediate danger. It is going to affect you and it will certainly affect your children. While there is the injustice that the poorest will be worst affected, you will be affected too," said Montgomery.

The report says evidence on greenhouse gas emissions, temperature and sea-level rises, the melting of ice-sheets, ocean acidification and extreme climatic events suggests the forecasts by the Intergovernmental Panel on Climate Change in 2007 might be too conservative. The UK target, to limit global warming to two degrees more, is unlikely to be achieved.

Costello, however, said the message from the report was not entirely negative. "There is an awful lot we can do," he said. Reducing carbon emissions would encourage people to cut use of vehicles, and if that led to more walking and cycling it would tend to lower stress levels, reduce obesity, and lessen heart disease, lung disease and stroke risks.