This article was written by Seth Borenstein and was published in the Toronto Star on October 31, 2023.

In a little more than five years — sometime in early 2029 — the world will likely be unable to stay below the internationally agreed temperature limit for global warming if it continues to burn fossil fuels at its current rate, a new study says.

The study moves three years closer the date when the world will eventually hit a critical climate threshold, which is an increase of 1.5 degrees Celsius since the 1800s.

Beyond that temperature increase, the risks of catastrophes increase, as the world will likely lose most of its coral reefs, a key ice sheet could kick into irreversible melt and water shortages, heat waves and death from extreme weather dramatically increase, according to an earlier United Nations scientific report.

Hitting that threshold will happen sooner than initially calculated because the world has made progress in cleaning up a different type of air pollution — tiny smoky particles called aerosols. Aerosols slightly cool the planet and mask the effects of burning coal, oil and natural gas, the study’s lead author said. Put another way, while cleaning up aerosol pollution is a good thing, that success means slightly faster rises in temperatures.

The study in Monday’s journal Nature Climate Change calculates what’s referred to as the remaining “carbon budget,” which is how much fossil fuels the world can burn and still have a 50 per cent chance of limiting warming to 1.5 C since pre-industrial times. That is the threshold set by the 2015 Paris Agreement.

The past 10 years are already on average 1.14 C hotter than the 19th century.

Last year was 1.26 C warmer and this year is likely to blow past that, according to scientists.

The new study set the carbon budget at 250 billion metric tons. The world is burning a little more than 40 billion metric tons a year (and still rising), leaving six years left. But that six years started in January 2023, the study said, so that’s now only five years and a couple of months away.

“It’s not that the fight against climate change will be lost after six years, but I think probably if we’re not already on a strong downward trajectory, it’ll be too late to fight for that 1.5-degree limit,” said lead author Robin Lamboll, an Imperial College of London climate scientist.