Extreme heat waves could hit the world every year by 2075

Sweltering heat waves that typically strike once every 20 years could become yearly events across 60 percent of Earth's land surface by 2075 if greenhouse gas emissions continue unchecked, says a study.

However, if emissions are aggressively cut, the severity of these 20-year events could be significantly reduced over the majority of the world's land areas, though portions of the Earth would still face dangerous heat extremes, the researchers said.

For example, in 2075, almost a quarter -- instead of more than a half -- of land areas could experience 20-year heat waves that are at least five degrees Celsius hotter than today's.

"But even with such dramatic reductions in carbon dioxide emissions, future heat waves will be far more dangerous than they are now," said one of the researchers Michael Wehner from Lawrence Berkeley National Laboratory in the US.

The study, published in the journal Climatic Change, quantified the benefits society would reap, in terms of avoiding extreme heat events, if action is taken now to mitigate climate change.

"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 from the US National Center for Atmospheric Research (NCAR) in Colorado.

"Even though heat waves are on the rise, we still have time to avoid a large portion of the impacts," Tebaldi noted.

The researchers used data generated by the NCAR-based Community Earth System Model to study 20-year extreme heat events -- those intense enough to have just a one-in-20 chance of occurring in any given year.

The researchers looked at two things: how frequently today's typical 20-year heat wave may occur in the future, as well as how much more intense future 20-year heat waves will be.

Besides finding that today's 20-year heat waves could become annual occurrences across more than half of the world's land areas by 2075, the study also concluded that heat waves with a one-in-20 chance of occurring during a future year will be much more extreme than heat waves with the same probability of occurring today.

For example, if emissions remain unabated, such a heat wave in 2050 would be at least three degrees Celsius hotter for 60 percent of the world's land areas. For 10 percent of land areas, a 20-year heat wave in 2050 would be at least five degrees Celsius, the study projected.