Nick Obradovich couldn’t sleep. It was October 2015, and a surprise heat wave sent thermometers across San Diego soaring 7 degrees Fahrenheit above average. The window air-conditioning unit in his living room wasn’t powerful enough to cool the bedroom. So the climate impact researcher lay on top of his sheets, fixated on the idea that global warming could forecast many more nights like that one.

Turns out that may be the case. Surges in nighttime temperatures correspond with an increase in self-reported nights of restless and insufficient sleep, according to a study Obradovich published Friday in the journal Science Advances.

“Human sleep relies on ambient temperature for its regulation,” Obradovich, now a postdoctoral fellow at Harvard University’s John F. Kennedy School of Government, told HuffPost by phone this week. “When that ambient temperature is unusually warm, when it’s not expected to be, that can predict disruption in sleep patterns.”

To test his theory, he and three other researchers compared U.S. responses from 765,000 people surveyed by the Centers for Disease Control and Prevention between 2002 and 2011 to local weather data. On hotter-than-normal nights, more people said they struggled to fall or stay asleep.

That bodes ill for the future: Temperatures are forecast to rise more than 3.5 degrees Fahrenheit above pre-industrial levels by the end of the century as burning fossil fuels, industrial farms and deforestation emit more planet-warming gases into the atmosphere. An increase that large would yield catastrophic results as ice caps melt and glaciers retreat. Antarctic ice melt alone could send sea levels surging by up to 49 feet by 2500, a study released in March 2016 found.

Christopher Aluka Berry/Reuters Rising temperatures -- caused by coal-fired power plants, such as the one pictured above in Georgia, and other human activities -- could disrupt sleep around the world.

Climate change already affects low-income people disproportionately, as rising sea levels destroy low-lying homes, pollution worsens costly diseases and droughts make food and water scarcer and more expensive. Now add poor sleep to that list.

“Poorer people are more likely to have disruptions in their sleep, probably due to the fact that they don’t have air conditioning or, if they have it, can’t afford to use it the whole night during summer,” said Obradovich, who also works as a researcher at the Massachusetts Institute of Technology’s Media Lab.

“It’s not just sleep,” he added. “It’s sleep in the bigger picture of the other factors climate change is likely to impact.”

Obradovich said he would like to replicate the study with data from hotter, poorer countries closer to the equator.

“If we were to have data from India or Brazil on the relationship between unusually warm nights and sleep, we might observe substantially larger effects,” he said. “If we do see larger effects in those countries, that’s an even further example of how climate change is going to affect people across the world.”

Aggressive reductions in greenhouse gas emissions could limit the rise in global temperatures. But, even as carbon emissions plateaued over the past two years, that seems unlikely in the near term. President Donald Trump has already scrapped policies crucial to meeting U.S. commitments under the Paris Agreement, the first climate deal to include China and the U.S., the world’s biggest emitters. But the White House is considering pulling out of the accord amid its massive push to increase fossil fuel production across the country. Without U.S. participation, the deal ― a symbolic first step toward slashing emissions, but not enough to halt the calamitous temperature increases forecast by most climatologists ― could fall apart.

Improvements in air conditioning that make the technology cheaper and more widely available could help stave off some effects of warming temperatures. But air conditioning sucks up a lot of electricity, and the utility sector ― dependent on burning coal and natural gas ― remains the largest emitter of greenhouse gases, at least in the U.S. So that solution may be like feeding a hungry snake its tail.