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El Niño may push heating past 1.5C but urgent action could avert catastrophe

May 06, 2023

Without emissions reductions, in next 10 years 1.5C target may be permanently exceeded

For several years, the world has been in the grip of La Niña, a weather system in the Pacific that tends to bring cooler temperatures around the world.

Despite that, there has continued to be strong rises in global surface temperatures, with some of the hottest years on record. This year, the oscillating Pacific weather system will probably turn to its opposite, the warming El Niño. That is likely to turbocharge temperatures, and within the next five years we can expect to see new records set, according to the World Meteorological Organisation (WMO).

The previous highest global annual average temperature above pre-industrial levels was 1.28C, but there is now a roughly two-thirds likelihood that surface temperatures will breach 1.5C for at least one of the next five years.

But the rise in temperatures could be temporary, the WMO said. While the trend marches upward, some years are still likely to be slightly cooler, and when the El Niño weather system eventually wanes again and re-enters the opposing, cooling La Niña phase, that could bring down levels from their peaks.

Mark Maslin, a professor of Earth system science at University College London, said: "Within the next five years the extra warming that comes with El Niño events will temporally push the global climate over the 1.5C. It may then drop back below 1.5C, allowing climate change deniers to tell everyone the world is now cooling – as they always ignore the long-term trend."

But he said any respite would be temporary. "Global [greenhouse gas] emissions have yet to drop, and emissions in 2022 were the highest in human history. Hence the long-term warming trend will continue, and without emission reductions we could pass 1.5C permanently in the next 10 years."

Even if that does happen, the temperature goal in the Paris agreement is still worth fighting for, Maslin argues. "This does not mean we should give up on the 1.5C target – far from it. It was an ambitious and aspirational target set by all nations at the Paris climate conference in 2015 and at Cop28 we must re-enforce the global commitments to reduce greenhouse gas emissions as quickly as possible.

"If we ultimately fail to keep global climate to below 1.5C, then we fight for 1.6C and then 1.7C and then 1.8C – because as scientists we know that every 10th of degree of warming will make a huge difference to the impacts of climate change. And the extreme weather events we have experienced over the last few years are just a warning shot to what is to come if we cannot switch to cleaner energy and lifestyles."

Bob Ward, a policy director at Grantham Institute at the London School of Economics, adds: "The 1.5C target refers to the trend in global average temperature, and not just a single year. While we may breach the threshold for a year in the near future, the main risks are associated with the trend reaching 1.5C within the next couple of decades, when most years will be 1.5C or warmer than the pre-industrial level."

Some people have tried to argue that the 1.5C threshold is a political rather than a scientific target. There will be serious impacts on the climate at 1.4C of warming, and 1.6C, and so on, observes Friederike Otto, a senior lecturer in climate at Imperial College London. But science shows that we should not regard 1.5C as without harm.

Otto said: "There will be more irreversible consequences at 1.6C than at 1.5C, but there will also be irreversible changes at 1.4C compared with 1.3C. But we should not say that 1.5C is a safe limit – we are already at 1.2C of heating and people are dying, ecosystems are dying as a result. So 1.5C is a political compromise, not a safe physical limit."

Ward adds: "The 1.5C threshold is a political target, as identified in the Paris agreement, but it is based on science, particularly the assessment published in 2018 by the Intergovernmental Panel on Climate Change. It showed how the impacts increase significantly with warming beyond 1.5C, and the risks of crossing major thresholds also rise. The evidence that some impacts, such as intense heatwaves, are beginning to appear earlier than expected could be an indicator that the risks of breaching 1.5C have been underestimated."

Scientists know there are "tipping points" within the climate system, when warming triggers a cascade of impacts – for instance, the melting of the ice caps, or the point at which a drying Amazon turns from rainforest to savannah. More of these tipping points are likely to be triggered, the higher temperature goes.

There are actions we could take to try to reduce global heating in the short term, chief among them reducing emissions of the powerful greenhouse gas methane. Produced by inefficient fossil fuel operations, and from animal agriculture and waste, methane is about 80 times more potent in warming the atmosphere than carbon dioxide, but it is relatively short-lived, breaking down into carbon dioxide within about two decades. Plugging the leaks in oil and gas wells and coalmines would go a long way to reducing methane emissions, and could even be profitable with today's high gas prices, according to the International Energy Agency.

But any such measures must be accompanied by broader emissions reductions, as this is the only way to stop the upward march of temperatures.

Ward said: "Most analyses, including the IPCC Sixth Assessment Report, show that it will now be very difficult, given where we currently are, to stop the trend in temperature exceeding 1.5C within the next few decades. In that sense, the battle to keep 1.5 alive has probably failed.

"The world has failed to recognise the scale of the risks clearly spelled out by the scientists, and has failed to mount an adequate response. But that does not mean we should abandon the target as we can still avoid many serious impacts if we can bring down global mean surface temperature so it is lower than the 1.5C target by the end of the century."