The UK must be prepared to cope with weather extremes of at least 2 degrees Celsius of global warming by 2050, climate advisers have said.
The independent Climate Change Committee (CCC) said the UK is not adapted to worsening extremes such as 40 degrees heatwaves, droughts, wildfires and flooding that are already occurring at current levels of 1.4 degrees of warming, "let alone" what is to come.
In a letter to the UK government, the committee has urged ministers to set out stronger objectives and targets for protecting health, homes, food security, infrastructure and key public services, in the face of 2 degrees of warming by 2050 "at a minimum".
And the committee said new homes, electricity networks and other infrastructure that is expected to last for decades, must be built with the potential to be adapted to cope with temperatures of as much as 4 degrees above pre-industrial levels by the end of the century.
The trees planted now for storing carbon and cooling cities must also be able to withstand future temperature rises.
The advice urges the UK to plan for climate change that is worse than the long-term temperature goal of the international climate treaty, the Paris Agreement, which aims to limit global warming to 1.5 degrees.
The committee said it continued to believe that the 1.5 degrees target was possible.
But "prudent risk management needs to consider a wider range of possible worse outcomes", with potentially faster rates of warming between now and 2050 leading to higher than the 2 degrees threshold by mid-century, while temperature rises of 4 degrees by the end of the century cannot be ruled out.
The letter comes in response to a request from the Government on advice on strengthening the objectives for adapting the UK to inevitable warming caused by greenhouse gas emissions, which the committee has long warned does not have the same focus as efforts to cut those emissions.
This year the UK has had its hottest summer on record, with much of the country in drought, and one of the worst harvests on record.
That came hot on the heels of 18 months of record-wet weather, and before that temperatures topped 40 degrees in the UK for the first time in 2022, causing a spike in heat deaths and destructive wildfires.
The committee is planning to release a major report on how the UK can adapt to climate change, next May, in which it will set out further details of what needs to be done to prepare the country for climate change.
But it has called for a framework of clear long-term objectives for adapting the UK to climate change by 2050, driven forward with targets every five years, and for government departments to be clearly accountable for delivering them.
The committee warns that global warming of 2 degrees above preindustrial levels will lead to more frequent, powerful and increasingly unprecedented extremes of weather hitting the UK.
The chances of a heatwave occurring each year will double, while the time spent under drought conditions across England is also expected to double.
Sea levels will rise, peak rainfall across the UK is expected to increase by up to 10-15% on the wettest days, and peak river flows will increase by up to 40% for some catchments, raising the risk of flooding.
The risk of wildfires will also rise, with increases in days with conditions highly favourable for blazes to break out, while wildfire season will extend into the autumn, the experts warned.
The committee said the government needed to deliver a future where impacts on people's health and wellbeing from rising temperatures are minimised, the UK's food security is preserved and support for nature is delivered despite climate change.
Key infrastructure must function as well as it does today, or even better, and cities, towns and villages should not be disrupted and vital services such as health and social care should continue to operate normally in extreme weather.
People should continue to have access to key services such as insurance.
Baroness Brown, chairwoman of the adaptation committee for the CCC, said: "People in the UK are already experiencing the impacts of a changing climate, and we owe it to them to prepare, and also to help them prepare.
"We need to see Government treating adaptation with the same urgency that we have been able to treat cutting emissions," she said.
"Both are absolutely essential and must go hand in hand."
She added: "This is not an either/or, adaptation is not an alternative to continuing to reduce our emissions globally as fast as we can."
Baroness Brown also criticised Conservative leader Kemi Badenoch, who has pledged to scrap the Climate Change Act, which created the committee and the framework for cutting emissions to net zero by 2050 and adapting the UK to climate impacts.
She said it was "very disappointing" to see cross-party support fracturing for action to cut emissions.
"I hope this is a moment where we aren't going to lose the consensus about the need to address climate impacts, the need for adaptation.
"I hope she (Ms Badenoch) will reflect on the fact the Climate Change Act covers both adaptation and mitigation," she said.
