NEW YORK • Global warming caused by human emissions of greenhouse gases is having clear effects on the physical world: more heatwaves, heavier rainstorms and higher sea levels, to cite a few.
In recent years, though, social scientists have been wrestling with a murkier question: What will climate change mean for human welfare? Forecasts in this realm are tricky, necessarily based on a long chain of assumptions. Scientific papers have predicted effects as varied as a greater spread of tropical diseases, fewer deaths from cold weather and more from hot weather, and even bumpier rides on airplanes.
Now comes another entry in this literature: A prediction that in a hotter world, people will get less sleep.
In a paper published on Friday by the journal Science Advances, Dr Nick Obradovich and colleagues predicted more restless nights, especially in the summer, as global temperatures rise. They found that the poor, who are less likely to have air-conditioning or be able to run it, and the elderly, who have more difficulty regulating their body temperature, would be hit hard.
If global emissions are allowed to continue at a high level, the paper found, by 2050 every 100 people in the United States may endure an extra six nights of insufficient sleep per month. By 2099, that could double to 14 nights.
Dr Obradovich, a political scientist who researches both the politics of climate change and its likely human impacts, and holds appointments at Harvard and the Massachusetts Institute of Technology, got the idea for the study while enduring a 2015 heatwave in an apartment in San Diego with no air-conditioner in the bedroom.
To calculate the effect of warmer temperatures in the future, he turned to data collected by the Centres for Disease Control and Prevention, which asks people in a survey to recall their sleep patterns in the previous month. Sure enough, he found a correlation between higher temperatures in particular cities and disturbed sleep.
To make forecasts, he used computer estimates of how hot particular places will get if greenhouse emissions continue at a high level. Dr Obradovich acknowledged that a survey about sleep over the previous month was subject to the vagaries of memory. Another big weakness in the study, perhaps, is that it is impossible to know what society will look like in a century's time.