Global warming in your bedroom - Potential casualty: sleep

G.S. Mudur May 26: Global warming melts glaciers, drives up sea levels and makes extreme weather events more common. If that makes you yawn, consider this: it may also disrupt human sleep.

So feel scientists who carried out the largest ever investigation into the link between sleep and temperature.

The study, which explored how temperatures may have influenced sleep and relied on data from 765,000 people across the US, has provided what scientists say is the "first evidence" that climate change may cause people to sleep less.

The researchers found that unusually warm nights are associated with less sleep, particularly during summer and among people with low incomes who are less likely to have access to air-conditioning through the night.

Their analysis, published today in the journal Scientific Advances, has suggested that a 1 degree Celsius rise in the night temperature produces an increase of approximately three nights of poor sleep per 100 individuals per month.

If this result is extrapolated across the US, a 1 degree Celsius rise in the night temperature would translate into 9 million additional nights of insufficient or poor sleep per month.

"Climate change could make getting a good night's rest more difficult in the coming decades," Nick Obradovich, a researcher at Harvard University and the Massachusetts Institute of Technology and the lead author of the study, told The Telegraph.

"We're likely to see many more warm night-time temperatures in future due to climate change," Obradovich added. "While sleep is only one factor among many, it is part of the mosaic of the social impacts of climate change - these impacts are likely to be quite costly to society."

Sleep researchers say the findings are not surprising. "The connection between temperature and sleep is well-known," Manvir Bhatia, a senior neurologist and head of the Neurology and Sleep Centre in New Delhi, said. Sleep is associated with a slight decrease in the core body temperature.

Earlier laboratory studies have shown that exposure to elevated temperatures can prevent the core body heat from being shed and contribute to poor sleep. "The implications are significant - climate change may make poor sleep more widespread across communities," said Bhatia.

Doctors have long viewed insufficient sleep as a risk factor for multiple health disorders - cardiovascular diseases, diabetes, obesity and a weakened immune system, among others.

Obradovich and his colleagues analysed sleep patterns reported by 765,000 US residents over a 10-year period, between 2002 and 2011, analysing average night temperatures and the reported nights of insufficient sleep.

Their analysis has also shown that the impact of night temperatures on sleep varies with the seasons - the effect is almost three times higher in summer than in spring, autumn or winter.

The researchers also studied sleep patterns segregated across different levels of income and age and found that low-income and elderly individuals may be the most susceptible to the effects of increasing night temperatures on sleep.

The average surface global temperature has increased by 0.85 degree Celsius between 1880 and 2012, according to the International Panel on Climate Change, a global body of scientists and climate policy specialists. It has been projected to increase by anywhere between 1.7 to 4.8 degrees Celsius over the coming decades if the world does not reduce emissions of earth-warming greenhouse gases.