Britain must spend £11billion every year to "prepare for the impacts of climate change", the Government's advisory body has said.
In a rallying cry to make the country open its wallets and protect against global warning, the Climate Change Committee has claimed the "British way of life" is under threat.
The £11billion figure would be shared between public and private sectors, it added - but might even underestimate what is truly needed.
"We need to recognise that there are aspects of our British way of life which are now really under threat from climate," said Baroness Brown, chairwoman of the CCC's Adaptation Committee.
The UK was "built for a climate that no longer exists", the committee said.
The CCC is also urging ministers to set maximum temperature limits for workplaces - which have been backed by unions.
"It's a very sensible thing to do because we know that productivity drops very significantly when the weather gets very hot and we know that people become more prone to making mistakes and to having accidents," Baroness Brown said.
Installing air conditioning and cooling systems in schools and hospitals should rank among the Government's top priorities, according to the committee.
Baroness Brown laid into what she called the "woeful" performance of successive governments in addressing the climate.
Britain must spend £11billion every year to 'prepare for the impacts of climate change', the CCC has said
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"It's not rocket science - we know what to do [but] we haven't yet seen a Government that's prepared to prioritise adapting to the change of climate [... and] protecting the people and the places that we love," she added.
The committee said extreme heat was the single greatest health risk from climate change facing Britain.
Over 90 per cent of existing homes could become dangerously hot during severe heatwaves, the CCC warned - and has demanded Britons rush to install air conditioning and heat pumps as a result.
The CCC has also raised fears of a double threat, predicting winter flooding and summer droughts will rock the nation.
Peak river flows in certain areas could surge by up to 45 per cent during intense rainfall by mid-century, the advisory body said.
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Baroness Brown argued the 11-figure annual spend would be 'very good value'
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While England's public water supply could face shortfalls of more than five billion litres a day without urgent action, driven by hot, dry summers and population growth.
Last year was the UK's warmest on record, with drought affecting much of the country.
Trade unions have thrown their support behind calls for workplace temperature caps.
The GMB said it makes "no sense whatsoever" that minimum temperature standards exist, but no legal heat limits.
"Sweltering heat is loads of fun if you're swanning around by the pool but if you've got a job to do it can be downright dangerous," said GMB senior organiser Lib Whitfield.
Last year was the UK's warmest on record, with drought affecting much of the country
| PA"Bosses need to do everything possible to keep workplaces cool, and more importantly, safe."
Unison's assistant general secretary Jon Richards also setting a maximum temperature for workplaces was "essential".
"Being too hot at work puts people's health at risk and leads to poorer performance and lower productivity," he said.
Baroness Brown argued the 11-figure annual spend was "very good value" compared to the "cost of the impacts of the climate that we're already seeing".
The up-front investment, her committee says, would save the UK tens of billions of pounds per year in the long run.
In response to the CCC's advice, Environment Secretary Emma Reynolds said: "We are acting to protect people and places from the impacts of climate change that are already being felt across the UK - from flooding to extreme heat and drought.
"Robust, independent science is essential and we will carefully consider the Climate Change Committee's latest recommendations to drive further action."