Climbing nighttime temperatures, driven by climate change, may harm human sleep, a new study revealed, with the poor and elderly most affected.
"What our study shows is not only that ambient temperature can play a role in disrupting sleep but also that climate change might make the situation worse by driving up rates of sleep loss," Nick Obradovich, who conducted much of the research as a doctoral student in political science at the University of California San Diego, said in a statement.
In a study published this week by the U.S. journal Science Advances, Obradovich and colleagues looked at responses from 765,000 individuals across the United States who took part in a public health survey, alongside temperature data from 2002 to 2011.
They found that a one-degree Celsius increase in nighttime temperature translates to three nights of insufficient sleep per 100 individuals per month.
"To put that in perspective: If we had a single month of nightly temperatures averaging one degree Celsius higher than normal, that is equivalent to nine million more nights of insufficient sleep in a month across the population of the United States today, or 110 million extra nights of insufficient sleep annually," the study said.
The negative effect of warmer nights is most acute in summer, the research showed. It is almost three times as high in summer as during any other season.
It also revealed that those whose income is below 50,000 U.S. dollars and those who are 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 financially.
If climate change is not addressed, warmer temperatures could cause six additional nights of insufficient sleep per 100 individuals by 2050 and approximately 14 extra nights per 100 by 2099 in the United States, it predicted.
"The U.S. is relatively temperate and, in global terms, quite prosperous," said Obradovich, now a postdoctoral fellow at Harvard's Kennedy School of Government and a research scientist at the MIT Media Lab.
"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."