Flirting with climate danger: UN forecasts 2 in 3 chance of briefly hitting key heat limit soon

There's a two-out-of-three chance within the next five years that the world will temporarily reach the internationally accepted global temperature threshold for limiting the worst effects of climate change, a new World Meteorological Organization report forecasts.

It likely would only be a fleeting and less worrisome flirtation with the agreed-upon climate danger point, the United Nations weather agency said Wednesday. That's because scientists expect a temporary burst of heat from an El Niño will supercharge human-caused warming from the burning of coal, oil and gas to new heights and then slip back down a bit.

The 2015 Paris climate agreement set 1.5 C (2.7 F) as a global guardrail in atmospheric warming, with countries pledging to try to prevent that much long-term warming if possible. Scientists in a special 2018 United Nations report said going past that point would be drastically and dangerously different, with more death, destruction and damage to global ecosystems.

"It won't be this year, probably. Maybe it'll be next year or the year after" that a year averages 1.5 C, said report lead author Leon Hermanson, a climate scientist at the United Kingdom's Met Office.

But climate scientists said what's likely to happen in the next five years isn't the same as failing the global goal.

"This report does not mean that we will permanently exceed the 1.5 C level specified in the Paris Agreement, which refers to long-term warming over many years. However, WMO is sounding the alarm that we will breach the 1.5 C level on a temporary basis with increasing frequency," WMO Secretary-General Petteri Taalas said in a statement.

"A single year doesn't really mean anything," Hermanson said. Scientists typically use 30-year averages.

Those 66 per cent odds of a single year hitting that threshold in five years have increased from 48 per cent last year, 40 per cent the year before, 20 per cent in 2020 and 10 per cent about a decade ago. The WMO report is based on calculations by 11 different climate science centres across the globe.

The world has been inching closer to the 1.5 C threshold due to human-caused climate change for years. The temporary warming of this year's expected El Niño — a phenomenon that starts with a warming of parts of the central Pacific Ocean and then sloshes across the globe — makes it "possible for us to see a single year exceeding 1.5 C a full decade before the long-term average warming driven by human emissions of greenhouse gases does," said climate scientist Zeke Hausfather of the tech company Stripe and Berkeley Earth, who wasn't part of the WMO report.

"We don't expect the longer-term average to pass 1.5 C until the early-to-mid 2030s," Hausfather said in an email.

But each year at or near 1.5 C matters.

"We see this report as more of a barometer of how we're getting close, because the closer you get to the threshold, the more noise bumping up and down is going to bump you over the threshold randomly," Hermanson said in an interview. And he said the more random bumps over the mark occur, the closer the world actually gets to the threshold.

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Key in all this is the El Niño cycle. The world is coming off a record-tying triple-dip La Niña — three straight years of El Niño's cooler cousin restraining the human-caused warming climb — and is on the verge of an El Niño that some scientists predict will be strong.