Urgent action must be taken to protect Britain from flooding, deadly heatwaves, water shortages and an international food crisis that will all become increasing risks as the Earth warms, according to a Government report.

Writing in the Climate Change Risk Assessment report, leading scientist Lord Krebs stressed there was “no question” that the primary response to climate change should be to reduce greenhouse gases.

But he added that it was still “crucial to prepare for the inevitable changes” that will occur because of the emissions that have already been pumped into the atmosphere.

Flash Floods hit London

Commenting on the report, an American scientist said climate change was now happening “so rapidly that people around the world are noticing the changes in global warming and extreme weather with their own eyes and skin”.

The report by the Committee of Climate Change (CCC), which advises the Government, predicts that even if the world manages to keep the average warming to 2C, there would be a 30 per cent decrease in the amount of water in rivers during droughts and up to a 20 per cent increase during periods of heavy rain.

In south-east England, the number of heat-related deaths would increase by 700 to 1,000 a year.

Global warming of 4C would result in “increasingly severe” impacts that “may not be avoidable through adaptation”. The report says there would be “high risks to people from extreme weather events” and “very high risks to vulernable groups”. Demand for water would be greater than the supply in a fifth of river catchment areas; 70 per cent of agricultural land would be classed as “poor” and the cost of flood damage would triple.

The report said there was an "urgent case for stronger policies" to address flooding, the health effects of heatwaves, water shortages, the risk to ecosystems, soils and biodiversity, and even the supply of food.

"Risks to the UK food system arise from an increasing risk of extreme weather events affecting both production and supply chains. Incremental changes in temperature, rainfall patterns and ocean acidification are also likely to shift the global pattern of food production posing risks to the price of food in the UK," it said.

In the report, Lord Krebs, who chairs the CCC's adaptation sub-committee, said while the world should continue to try to limit global warming, it was also time to prepare for the worst.

“There is no question that the primary response to climate change should be to reduce greenhouse gas emissions to limit further climate change," he said.

“But at the same time it is crucial to prepare for the inevitable changes that will result from the gases that have already been released into the atmosphere and that will continue to be emitted for some time to come.

“Even when the full impacts of climate change will not be felt for several decades, it may be a matter of urgency to act now, because of the long-term consequences of today’s decisions.

“The six immediate priority areas are related to risks of flooding and coastal change, the impact of high temperatures in the built environment, risks to natural capital, risks of future water shortages, impacts on the global food system, and risks arising from new and emerging pests and diseases.”

While the report described the recent international climate deal signed in Paris last year as a “significant step forward”, it also noted that Government’s commitments to reduce emissions would still lead to an estimated 2.7C rise.

“Global emissions would need to peak soon and then decline rapidly for the Paris Agreement goals to be feasible,” it says.

“Even in this scenario the uncertain sensitivity of the climate to greenhouse gases means there would remain at least a small chance of 4C or more of warming by 2100.

“It is therefore prudent to prepare for further warming whilst pursuing more stringent emission reductions as part of the global effort.”

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Dr Jeffrey Kargel, of Arizona University’s Department of Hydrology and Atmospheric Science, said the report’s findings were “familiar all over the globe”.

“The regional details vary, but the UK's recent recorded warming and the projected rise in temperatures and increases of extreme weather events are typical and pervasive across the Earth's surface,” he said.

“I have seen it in melting glaciers from Nepal to Chile to Alaska. Climate change is occurring so rapidly that people around the world are noticing the changes in global warming and extreme weather with their own eyes and skin.

“At the uncontrolled end of the possible future warming scenarios, the amount of warming comes close to the amount of warming that caused the end of the ice age … so we're talking about geologically epochal climate change.”

Chris Rapley, professor of climate science at University College London, said that “given the shortfall of the pledges” made by the 195 nations in Paris “adaptation actions have to take a high priority”.