Sleepless nights are set to soar in the next three decades ... because of global warming, say scientists.
Rising temperatures will make it much more difficult to nod off - endangering millions of people’s health.
The elderly and the less well off will be worst hit, adding to the problems caused by climate change.
The researchers worked out the cost to sleep patterns across the US and said the findings could be applied to other temperate countries across the world.
Britain is already the most sleep deprived nation in Europe managing just six hours a night on average two hours less than the recommended amount.
The study published in Science Advances represents the largest real-world study to date to find a relationship between insufficient sleep and unusually warm night-time temperatures.
It’s also the first to apply it to projected climate change.
Political scientist Dr Nick Obradovich said: “Sleep has been well-established by other researchers as a critical component of human health.
“Too little sleep can make a person more susceptible to disease and chronic illness, and it can harm psychological well-being and cognitive functioning.
“What our study shows is not only ambient temperature can play a role in disrupting sleep but also climate change might make the situation worse by driving up rates of sleep loss.”
Research has shown humans sleep better in a cold bedroom with the ideal temperature 17 degrees centigrade.
Dr Obradovich said if climate change is not addressed 2050 could cost people in the US millions of additional nights of insufficient sleep per year.
By 2099, the figure could rise by several hundred million more nights of lost sleep annually.
Dr Obradovich was inspired by a heat wave that hit San Diego in October 2015.
He was having trouble sleeping. He also noticed fellow students at his California University campus were looking grumpy and bedraggled.
Dr Obradovich, now at Harvard University in Boston looked at nine years of data from 765,000 Americans who responded to a public health survey between 2002 and 2011.
This enabled him to link self-reported nights of insufficient sleep to daily temperature data from the National Centres for Environmental Information. Then he combined the effects with climate model projections.
Increases in night-time temperature of one degree centigrade equated to three nights of insufficient sleep a month for every 100 individuals.
To put that in perspective a single month of this would be equivalent to 9 million more nights of insufficient sleep across the population or 110 million extra nights of insufficient sleep annually.
The bad effect of warmer nights is most acute in summer - almost three times worse than any other season.
Those whose income is below $50,000 (£38,870) or aged 65 and older are affected most severely. For older people, the effect is twice that of younger adults.
And for the lower-income group, it is three times worse than for people who are better off.
Using climate projections for 2050 and 2099 by NASA Earth Exchange, the study paints a bleak picture of the future.
Warmer temperatures could cause six additional nights of insufficient sleep per 100 individuals by 2050 - with this more than doubling to 14 by 2099.
Added Dr Obradovich: “The US is relatively temperate and, in global terms, quite prosperous.
“We don’t have sleep data from around the world, but assuming the pattern is similar, one can imagine that in places that are warmer or poorer or both, what we’d find could be even worse.”
A survey last year found adults in the UK are among the worst sleepers in the world.
More than a third (37%) of Britons said they did not get the right amount of sleep.
A quarter listed getting a better night’s sleep a priority, beaten only by wanting to lose weight.