Global warming is likely to continue even if the world achieves net zero emissions as overheating of the planet is likely to persist and “ intensify dangerous climate change”, researchers have warned.
The UN Intergovernmental Panel on Climate Change’s latest best estimate is that warming will end at net zero carbon emissions – regarded a key target to be met by 2050 to meet the Paris Agreement target of containing temperature rise at 1.5 degrees.
But a new study by an international team including scientists at Imperial College London (ICL) and the University of Exeter (UE) warns significant warming could occur after that. They map uncertainty in current climate modelling of likely scenarios and propose a framework to better predict future warming.
“The resulting risks must inform climate mitigation and adaptation policies to protect future generations,” they conclude in a study published in Frontiers in Science on Tuesday.
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Prof Joeri Rogelj of ICL said: “These estimates come with substantial uncertainty, meaning there is a non-negligible chance that global warming will continue after net zero and intensify dangerous climate change.”
“Worldwide emissions reduction plans overlook this important risk, which should be urgently addressed at Cop28,” he added. “The take-home message is that the future is more uncertain than we think, and so we must adjust our climate mitigation policies to prevent further warming after net zero.”
“We are working on building better models, but should not wait until they are perfect before we act,” Prof Rogelj added. Their study is the first comprehensive analysis of many factors controlling global temperatures and provides a framework for improving warming predictions.
“Our analysis identifies the levers of global warming after net zero, and explains why current estimates are so uncertain,” said lead author Dr Sofia Palazzo Corner of ICL. “The potential of future climate risks in a net zero world makes the need to limit our initial disturbance to the planet even more imperative. Crucially for policy, a world that expects warming to continue after net zero will have an even smaller carbon budget to keep total warming below 1.5 degrees.”
Prof Michael Mann of the University of Pennsylvania said that despite its alarming message the study offered hope. “It reminds us that the obstacles to climate action are neither physical nor technological. At this point, they remain political. And history teaches us that political obstacles can be overcome,” he noted.
Global temperatures are regulated by multiple natural processes and feedbacks in the oceans, land and atmosphere. Carbon emissions have influenced many of these, triggering long-term changes which could last for centuries after net zero is reached.
“The melting of ice in polar regions is one example,” said Prof Martin Siegert of UE
“As we have observed in the Arctic Ocean, and recently in the Antarctic, a thin layer of floating ice helps reduce global temperatures by reflecting the sun’s energy back into space. However, once this ice melts this reflection is replaced by absorption of solar energy, which drives temperatures even higher.”
Even current climate models show these processes could cause significant warming after net zero – with an estimated one in six chance this warming could exceed 15 per cent of total global warming.
“This means that if global temperatures have risen by 2 degrees at the point we reach net zero, the final temperature change could be above 2.3 degrees,” Prof Siegert said. “Warming of this magnitude would worsen big climate risks to communities across the world, and particularly in the most vulnerable regions.”
Despite progress in exploring climate risks, models are expensive to run and every added process further increases the computational burden. “We need a collaborative effort between diverse climate experts to develop a suite of scientific tools that allow us to more deeply explore and understand the level of global warming we can expect,” Prof Rogelj said.
The study identifies 26 processes, of which more than half could drive significant warming, including a decline in land carbon uptake. Plants are important mitigators of global temperatures since they use CO² but changing rainfall patterns, droughts and heatwaves, reduce the efficacy of this “carbon sink”.
They had built a catalogue of processes that could affect global temperatures in a net zero world, “but we need to better understand their potential impact,” said Dr Palazzo Corner. “We propose a set of key research activities to reduce this uncertainty and improve warming predictions as quickly as possible.”
“We are working on building better models, but should not wait until they are perfect before we act,” said Prof Rogelj. “We must ... drastically reduce emissions now with the goal of achieving net zero CO² as soon as possible and preventing climate harm to future generations.”
