Climate change is the biggest global health threat of the 21st century because it could change patterns of mosquito-borne diseases, exacerbate food and water scarcities and threaten shelter, according to a new report released on Thursday.

The 40-page report, titled Managing the Health Effects of Climate Change, was released jointly by the Lancet and University College London. Researchers focused on the global health implications of climate change on six areas:

• Patterns of disease and mortality, such as the spread of mosquitoes carrying malaria to warmer high altitudes.
• Food security, such as declining crop yields that could lead to greater food insecurity worldwide, where one billion people currently have deficient diets.
• Water shortages that will lead to more gastroenteritis from poor sanitation and malnutrition.
• Shortage of housing in cities and human settlements.
• Extreme climatic events such as flash flooding that will overwhelm sewage systems.
• Population migration.

"The inequity of climate change — with the rich causing most of the problem and the poor initially suffering most of the consequences — will prove to be a source of historical shame to our generation if nothing is done to address it," the authors wrote.

The researchers looked at how the Intergovernmental Panel on Climate Change projections of an average global temperature rise of two to six degrees above pre-industrial average temperatures would result in more heat waves, such as one in 2003 that caused up to 70,000 deaths in Europe.

The medium-risk scenarios predict a rise of four to five degrees in northern Canada, Greenland and Siberia.

"There are major health benefits from low-carbon lifestyles, which can reduce obesity, heart and lung disease, diabetes and stress," said lead author Prof. Anthony Costello of University College London's Institute for Global Health.

Costello called on health-care professionals to emphasize the threat greenhouse gas emissions and deforestation pose to future generations.

The loss of healthy years of life is predicted to be 500 times higher in Africa than in Europe, he said, urging that the inequity in health systems be addressed and poverty reduction take precedence in the debate on adapting human settlements.

Developing new crops to withstand higher temperatures is a major technological challenge, the report's authors said.

Even rich countries may not handle extreme weather events well, they said, noting that many people were trapped in New Orleans during Hurricane Katrina in 2005 because it hit at the end of a pay period, when workers lacked bus fare.

The commission that produced the report plans to hold a summit in two years to assess progress on its recommendations, such as reducing carbon emissions, increasing carbon biosequestration and equalizing the world's health systems.