Delays in net zero will make heatwaves hotter, longer and more frequent

Heatwaves could be hotter, more prolonged and frequent, the longer countries delay in reaching net zero emissions, a balance between greenhouse gases emitted and those taken out from the atmosphere, according to a modelling study.

Trends published in the journal 'Environmental Research: Climate' also indicate that heatwaves do not start to revert towards pre-industrial conditions for at least a millennium even after achieving net-zero targets.

Regions in the Southern Hemisphere are projected to experience heatwaves of significantly increasing severity when net zero was modelled to occur by 2050 or later.

Lead author Sarah Perkins-Kirkpatrick, professor of climate science at the Australian National University, said the work challenges a general belief that conditions after net zero will begin to improve for future generations.

"While our results are alarming, they provide a vital glimpse of the future, allowing effective and permanent adaptation measures to be planned and implemented," Perkins-Kirkpatrick said.

"It is still vitally important we make rapid progress to permanent net zero, and reaching global net zero by 2040 at the latest will be important to minimise the heatwaves severity," the lead author said.

China, the US and countries in the European Union are among those that have pledged to achieve net-zero emissions by 2050 during the UN Climate Change Conference 2021 or COP26, while India has targeted 2070 for reaching net zero. COP30 is ongoing in Belem, Brazil.

The authors wrote, "Delaying net zero beyond 2050 results in heatwave regimes that are worse than a transient 2 degrees Celsius warmer world."  Further, they "simply do not see a broadscale reduction in heatwaves for at least 1,000 years regardless of when net zero occurs".

Long-term (1,000 years) climate simulations were performed under net zero CO2 emissions using the Australian Earth system model 'ACCESS-ESM1-5'. A range of dates between 2030 and 2060 were chosen for achieving net zero and long-term differences in heatwaves for each five-year delay were calculated.

Co-author Andrew King from the University of Melbourne in Australia said throughout all scenarios, the longer net zero is delayed, the higher the occurrence of historically rare and extreme heatwave events.

"This is particularly problematic for countries nearer the equator, which are generally more vulnerable, and where a heatwave event that breaks current historical records can be expected at least once every year or more often if net zero is delayed until 2050 or later," King said.