Earth could cross a key climate threshold in two years. Here's why it matters.

Boston Globe

29-05-2025

The accelerated timeline is due to higher-than-expected temperatures over the past few years, diminishing air pollution that cooled the Earth, and greenhouse gas emissions that continue to rise globally, despite the growth of renewable energy.
And it means that irreversible tipping points in the climate system — such as the melting of Arctic ice sheets or the wide-scale collapse of coral reefs — are closer at hand than scientists previously believed.
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The WMO report predicted five more years of sky-high temperatures — which, combined with hotter conditions driven by the El Niño weather pattern, mean that the planet is poised to officially warm 1.5 degrees Celsius (2.7 degrees Fahrenheit) over a sustained period by 2027.
'There is no way, barring geoengineering, to prevent global temperatures from going over 1.5 degrees,' said Zeke Hausfather, a climate scientist and the climate research lead at the payments company Stripe. Geoengineering refers to deliberately cooling the planet, for example by injecting aerosols into the atmosphere — an idea that is hotly debated.
Nearly a decade ago, delegates from more than 190 nations agreed in Paris to pursue 'efforts to limit the temperature increase' to 1.5 degrees Celsius, after small-island nations protested that higher temperatures would sink their land beneath rising waves.
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While there is no official definition, most scientists and the UN Intergovernmental Panel on Climate Change understand the goal to be a long-term average temperature, over 20 or 30 years. (In a single year, temperatures could spike because of El Niño or other temporary factors.) That's why, when the world passed the first 12-month period of temperatures over 1.5 degrees Celsius in February 2024, scientists warned that this didn't mean the end of the target.
But now, with the WMO's new predictions, even that small hope has slipped away. According to the new analysis, it is likely that the next five years clock in, on average, at over 1.5 degrees Celsius. Combined with the past couple of hot years — and increasing temperatures expected after 2030 — that means 2027 is likely to be the first year where that long-term average temperature is over the limit, Hausfather said.
Since the 2015 Paris agreement, 1.5 degrees Celsius has been a kind of lodestar for the climate movement. Protesters have chanted 'Keep 1.5 alive' outside global climate meetings. Scientists have outlined how that level of warming will drive infectious diseases, destroy crops, and fuel weather disasters.
Still, the goal was always a stretch. In the accord, nations agreed to hold temperatures 'well below' 2 degrees Celsius and pursue efforts to hold them to 1.5 degrees Celsius. But even at the time, some scientists and experts privately worried that — given the difficulty of transforming the energy system — the more ambitious target would prove impossible.
'There's tremendous inertia in the industrial system,' said David Victor, a professor of public policy at the University of California San Diego, who has questioned the feasibility of the goal since before the Paris agreement. 'It doesn't change quickly.'
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A pumpjack dips its head to extract oil in a basin north of Helper, Utah.
Rick Bowmer/Associated Press
Although renewables have grown dramatically over the past decade, they still make up just about a third of the global energy mix. Even as wind, solar, and batteries grow on the grid, the world is also consuming more electricity than ever before.
Missing the target will mark the end of a hopeful phase in the world's battle against climate change — and the beginning of a period of uncertainty about what comes next. At the same time, humanity will face mounting weather extremes, including deadly heat waves that compound in strength for each tenth of a degree of warming.
It also places policymakers and negotiators who have tried to rally support for slashing planet-warming emissions in an uncomfortable situation. UN Secretary General António Guterres, for example, has claimed that the 1.5-degree goal is 'on life support' and 'will soon be dead.' At some point soon, nations will have to acknowledge that failure — and devise a new goal.
'You could imagine governments saying, 'Hey, 1.5 is not going to be feasible, but here's what we're going to do, and here's where we're going to tighten the efforts,'' said Victor. 'That's one approach. And another approach would just be to say give up.'
Some countries and scientists have also put their faith behind a concept called 'overshoot' — where the world could pass 1.5 degrees Celsius, then later on remove carbon dioxide from the atmosphere to bring temperatures back down. But many researchers warn that if countries cannot even spend the money to build out renewables and batteries, removing CO2 from the sky could be a pipe dream.
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'I'm personally very skeptical about our willingness to spend tens of trillions of dollars on dealing with overshoot,' Hausfather said.
Nations could redirect their attention to the Paris agreement's less ambitious goal — holding temperatures to below 2 degrees Celsius of warming. That goal is more feasible, but at the moment still unlikely. The planet is currently on pace for something closer to 2.5 degrees Celsius.
'It's just the longer we wait, the harder it's going to be,' Hausfather said. 'After another decade of doing nothing, we're going to talk about the 2-degree target much like we talk about the 1.5-degree target.'