Without reductions in planet-warming emissions, blistering heat waves of the strength that now typically occur once every 20 years could happen annually on 60 percent of the Earth's land areas by 2075, scientists are warning.
And intense heat waves -- defined as three exceptionally hot days in a row -- will become far more extreme if greenhouse gas emissions continue unchecked, said a new study published in the journal Climatic Change.
The researchers said a worsening of extreme heat could have potentially deadly effects.
"Imagine the hottest day that you can remember and instead of 42°C, it's now 45°C. That's going to have a dangerous impact on the poor, the old and the very young, who are typically the ones dying in heatwaves," said Michael Wehner of the Lawrence Berkeley National Laboratory in the United States.
By 2050, heat waves that happen on average once in 20 years would be at least 3°C hotter on 60 percent of the Earth's land areas than now. In 10 percent of the world, they would be at least 5°C hotter, the researchers said.
In December, around 195 countries agreed a new UN deal to try to restrain the rise in global average temperatures to "well below" 2°C above pre-industrial levels.
But the emissions cuts they have pledged so far are not enough to meet that goal.
The new research -- part of a larger project to quantify how emission reductions could affect health, agriculture, hurricanes, sea level rise and drought -- found that stringent mitigation measures could reduce heatwaves significantly.
"The study shows that aggressive cuts in greenhouse gas emissions will translate into sizable benefits, starting in the middle of the century, for both the number and intensity of extreme heat events," said Claudia Tebaldi of the National Center for Atmospheric Research, where the project is based.
"Even though heatwaves are on the rise, we still have time to avoid a large portion of the impacts," she added.