The agency's chief executive Baroness Young said current measures to adapt to a changing climate were "too little, too slowly", and an huge effort was needed to address the crisis.

Hilary Benn, Environment Secretary, warned the agency's annual conference in London that global warming was a challenge to security, migration, politics and economics as well as the environment.

Baroness Young told the conference that Britain would face more droughts, flooding, coastal erosion and loss of biodiversity as the climate altered. She said measures such as improving the resilience of existing homes to flooding, not building on floodplains and improving water use efficiency were needed.

Rising sea levels and coastal erosion threatened £130 billion worth of property around the coast, with the elderly and poor communities most vulnerable, and seaside settlements must have help adapting, she said.

"This is World War Three - this is the biggest challenge to face the globe for many, many years. We need the sorts of concerted, fast, integrated and above all huge efforts that went into many actions in times of war. "We're dealing with this as if it is peacetime, but the time for peace on climate change is gone - we need to be seeing this as a crisis and emergency," she said. She also said much needed to be done to reduce greenhouse gas emissions - or adaptation measures would need to massively increase.

But she criticised the proposed Severn Barrage project - which could generate nearly 5 per cent of the UK's electricity through renewables at the cost of the internationally-important wildlife sites in the estuary - as looking for paper to write on and "reaching for the Mona Lisa".

Robert Watson, chief scientist of the Department for the Environment, Food and Rural Affairs, was asked later whether Britain needed to spend 42 per cent of its budget on climate change as the United States did on the war in World War Two. He said tackling climate change required will but was possible at relatively little cost.


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