SINGAPORE - Nearly all of the world's population experienced higher temperatures from June to August as a result of human-induced climate change, according to a peer-reviewed research report published late on Thursday.

The northern hemisphere summer of 2023 has been the hottest since records began, with prolonged heatwaves in North America and southern Europe causing catastrophic wildfires and spikes in mortality rates. July was the hottest month ever recorded, while average August temperatures were also 1.5 Celsius higher than pre-industrial levels.

A study by Climate Central, a U.S.-based research group, looked at temperatures in 180 countries and 22 territories and found that 98% of the world's population were exposed to higher temperatures made at least twice more likely by carbon dioxide pollution.

"Virtually no one on Earth escaped the influence of global warming during the past three months," said Andrew Pershing, Climate Central's vice president for science.

"In every country we could analyse, including the southern hemisphere, where this is the coolest time of year, we saw temperatures that would be difficult - and in some cases nearly impossible - without human-caused climate change," he said.

Climate Central assesses whether heat events are made more likely as a result of climate change by comparing observed temperatures with those generated by models that remove the influence of greenhouse gas emissions.

It said as many as 6.2 billion people experienced at least one day of average temperatures that were at least five times more likely as a result of climate change, the maximum value in Climate Central's Climate Shift Index.

The heatwaves in North America and southern Europe would have been impossible without climate change, said Friederike Otto, a climate scientist at the Grantham Institute for Climate Change and the Environment.

"We have looked at isolated heatwaves," she said. "They have not been made five times more likely. They have been made infinitely more likely because they would not have occurred without climate change."