Climate change poses the biggest threat to human health in the 21st century but its full impact is not being grasped by the healthcare community or policymakers, a medical report concludes.

The report, compiled by a commission of academics from University College London and published in The Lancet, warns that climate change risks huge death tolls caused by disease, food and water shortages and poor sanitation.

The authors said that the NHS would face serious incremental pressures from heat and hygiene-related illnesses because of increasingly hot summers, greater pathogen spread with warmer temperatures, and the heightened risk of flooding.

Professor Anthony Costello, a paediatrician and director of UCL Institute for Global Health, said that he had not realised the full ramifications of climate change on health until 18 months ago.

Describing the threat as a "clear and present danger" that would affect billions of lives, he said that the world needed a 21st-century public health movement to deal with climate change. He added that failure to act will result in future generations feeling the same moral outrage as is felt today towards those "who brought in and did nothing to stop slavery".

"The big message of this report is that climate change is a health issue affecting billions of people, not just an environmental issue about polar bears and deforestation," Professor Costello, the commission leader, said. "The impacts will be felt not just in the UK, but all around the world — and not just in some distant future but in our lifetimes and those of our children."

The UCL Lancet Commission focused on six areas for their report, Managing the health effects of climate change: patterns of disease and mortality, food security, water and sanitation, shelter and human settlements, extreme events, and population migration.

The commission considered a number of ways that climate change could affect health. Changing patterns of disease and mortality would emerge in a greater rate of transmission and geographic spread of traditionally tropical endemic diseases such as malaria and dengue fever.

Heat will also have a serious effect on mortality, as will food and water security, with scientists predicting that crop yields could drop by 17 per cent with a 1C change in temperature.

Professor Costello said that the health lobby "had come to the issue late and should be saying more".

The commission said that there was the need for health leaders to join the debate on mitigation strategies — policies aimed at reducing greenhouse gas emissions to tackle climate change — and emphasise the importance of action. It added that there must be a focus on health systems, in particular the inequalities between developed and developing nations, and a drive by healthcare professionals to outline how adopting low-carbon lifestyles can improve human health, reducing obesity, heart and lung disease, diabetes and stress.

"We believe that all the main players — health, political, scientific, technological, and civil society must come together," Professor Costello said. "We have laid out a framework for action, and we have called for a collation of information on the health effects of climate change. We need a new 21st-century public health movement to deal with climate change."

An international team of researchers, led by Professor Sir Andrew Haines from the London School of Hygiene and Tropical Medicine, is investigating the potential health benefits of reducing greenhouse gas emissions. The results of the study will inform the UN Climate Change Conference in Copenhagen in December this year.

Professor Mark Maslin, director of UCL’s Environment Institute and a co-author, said that it should act as "Stern Report for Health and for medics", in reference to the economic review of climate change conducted by Sir Nicholas Stern.

Richard Horton, the editor of The Lancet, added: "This really hasn’t been an issue on the table for anyone in health over the last 10 years. They must take a leading part in this debate."

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