The world reached a grim milestone in 2024: for the first time ever, scientists said Thursday, the planet warmed 1.5 degrees Celsius over preindustrial levels. This year, which scientists said is also “virtually certain” to be the hottest year on record, shows the need for urgent, ambitious action—especially in the leadup to COP29 in Baku.
“Seeing a single year having temperature[s] that are 1.5 C higher than preindustrial conditions is a wake-up call,” said Joeri Rogelj, Director of Research at the Grantham Institute at Imperial College London.
What are the implications of this new milestone for the future of climate diplomacy—and the planet? Here’s what you need to know.
Why is 1.5 degrees C significant?
It’s not just an arbitrary number. Rather, 1.5 degrees C is a critical milestone beyond which the effects of climate change become increasingly dangerous and potentially irreversible. It also marks the line between difficult adaptation and widespread catastrophe. Science has shown that if warming exceeds 1.5 degrees C by the end of this century, the chances of extreme storms and heatwaves skyrocket; sea level rise could put millions at risk; and coral reefs could suffer catastrophically.
As of 2024, we’ve already heated the world by about 1.3 degrees C on average since the Industrial Revolution, thanks to our reliance on fossil fuels. The effects of climate change scientists have warned about for decades have already arrived. The closer the world moves towards 1.5 degrees C, the more we are moving into uncharted and perilous territory—and the more urgent it becomes that we take action to cut our emissions.
“We understand that natural variations mean that 2024 was slightly warmer than the underlying global warming trend in isolation,” said Rogelj. “But these variations only contribute a few tenths of a degree variations up or down, and therefore clearly show the urgency of limiting the global warming trend.”
What does breaking 1.5 degrees C mean for the Paris Agreement?
The Paris Agreement looks at temperatures over a longer time period than just one year. But seeing temperatures like this is a warning sign that the world is not on the right trajectory. Experts say that without massive and swift global changes, it is likely that warming will rise above the 1.5 degrees C level by around 2035, according to the IPCC’s last report in 2023.
“These elevated temperatures come with painful knock-on effects in the shape of more extreme weather,” said Rogelj. “For events over the past years, science can now with greater confidence than ever pinpoint the fingerprint and contribution of human-caused climate change to these events. Heatwaves that killed thousands across the globe, floods that wreak havoc in conflict-ridden regions such as Libya, or wildfires that burn millions of hectares in Canada have all found to be exacerbated by climate change.”
That doesn’t mean the goal is impossible: rather, the case for ambitious action only becomes stronger. Governments and businesses must come together to act and avoid the disastrous—and expensive—ramifications that breaching 1.5 degrees C would entail. The world has much of the science and solutions it needs, experts say: it’s simply a matter of scaling up action immediately.
Is it possible to temporarily exceed 1.5 degrees C and return below it later? What would the impacts be in that scenario?
The science is still not clear on this. While IPCC’s sixth assessment (AR6) includes several pathways to keep warming under 1.5 degrees C that incorporate overshoot possibilities, those possibilities deal only with median warming outcomes. A paper published earlier this year in Nature found that when considering the potential for feedbacks—fundamental changes in some of Earth’s most crucial processes as a result of higher warming—warming could spike much higher than main IPCC projections, and create uncertain outcomes.
“Global and regional climate change and associated risks after an overshoot are different from a world that avoids it,” the paper states. “…Temperature reversal could be undercut by strong Earth-system feedbacks resulting in high near-term and continuous long-term warming.”
What scientists agree on is that even if it is possible to bring temperatures back down again and keep feedbacks to a minimum, some of the impacts the world will see in the meantime—lives lost in extreme heatwaves, damage from floods and hurricanes—are irreversible. Global attention, experts say, must focus on keeping warming as close as possible to 1.5 degrees C.
What are the main steps to limit warming to 1.5 degrees C?
To stabilise temperatures at 1.5 degrees C, we need to reach net-zero emissions globally around 2050. This means balancing the greenhouse gases we emit with those we remove from the atmosphere.
The science is clear that in order to avoid passing 1.5 degrees C, we must transition off of fossil fuels: no new oil, gas, or coal development. World leaders also must undergo a rapid transition to renewable energy. Investing in and innovating new technologies and electrifying everything—from cars to heating systems—will also be important, as will restoring nature and shifting to a circular economy. Finally, adapting infrastructure, health services, and farming practices to cope with the monumental changes that are already underway will be crucial.
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