Professor Kevin Anderson, Director of the Tyndall Centre for Climate Change Research, said Government and local authorities are failing to grasp the risks to Britain of global warming.
He accused people of focusing on the chance of warmer evenings, rather than realising heatwaves will cause deaths.
"We may like to think of it as a nice café culture, sitting outside sipping lattes – but we will be struggling to sleep because our buildings won't cool down at night.
"That's when you see the deaths occurring. We can think about this in advance."
The Met Office predicts that summer temperatures will could rise by up to 5C by the 2080s.
Heatwaves, like the one that killed 2,000 people in 2003, could become more frequent.
Prof Anderson pointed out that UK buildings and hospitals are not equipped for these temperatures.
He called on politicians to 'bite the bullet' by upgrading houses so ventilation is better and making sure hospitals are prepared for illness caused by heat.
Prof Anderson also said flooding could become more frequent because of rising sea levels and more intense rainfall.
Last year was the wettest on record and the Met Office has warned that the frequency of extreme rainfall in the UK may already be increasing.
He said councils have to improve drainage in cities and ensure homes are prepared and not built on flood plains.
However, first Prof Anderson said the UK must try to prevent climate change from happening so fast and temperatures reaching dangerous levels by reducing carbon emissions.
He recommended investment in public transport and renewable energy.
"The new president of the World Bank has said he expects to see people fighting for food and water everywhere.
"Hopefully we would be more organised and find a rationing system.
"We are not talking about many many generations away. We are talking about our own lifetimes and the lives of our children." More