A new study warns that exceeding 1.5°C, even briefly, causes irreversible climate impacts. Immediate action to achieve net-negative emissions is essential.
A new study published today in Nature warns that, while it may be possible to reverse global temperature increases after a temporary overshoot of 1.5°C, some climate impacts, such as rising sea levels and other damages experienced at peak warming, will be irreversible.
The study is the culmination of a three-and-a-half-year project, backed by the European innovation fund HORIZON2020, looking at so-called ‘overshoot’ scenarios where temperatures temporarily exceed the Paris Agreement’s 1.5°C limit, before descending again by achieving net-negative CO2 emissions.
“This paper does away with any notion that overshoot would deliver a similar climate outcome to a future in which we had done more, earlier, to ensure to limit peak warming to 1.5°C,” explains Carl-Friedrich Schleussner, Integrated Climate Impacts Research Group Leader in the IIASA Energy, Climate, and Environment Program and scientific advisor at Climate Analytics, who led the study. “Only by doing much more in this critical decade to bring emissions down and peak temperatures as low as possible, can we effectively limit damages,” he adds.
It matters how high and for how long we let temperatures rise
The paper highlights that if we were to exceed 1.5°C there are clear benefits to reversing warming by acting to achieve net negative emissions globally. Achieving long-term temperature decline could lower sea level rise in 2300 by about 40 cm compared to a situation in which temperatures merely stopped rising.
“Until we get to net zero, warming will continue. The earlier we can get to net zero, the lower peak warming will be, and the smaller the risks of irreversible impacts,” notes study co-author Joeri Rogelj, professor of climate science and policy and Director of Research of the Grantham Institute at Imperial College London and senior research scholar in the IIASA Energy, Climate, and Environment Program. “This underscores the importance of countries submitting ambitious new reduction pledges, or so-called Nationally Determined Contributions (NDCs), well ahead of next year’s climate summit in Brazil.”
Full carbon dioxide removal capacity is needed to hedge against higher warming
The study emphasizes that while there are still pathways open to limiting warming to 1.5°C or lower in the long run, there is a need to ‘hedge’ against higher warming outcomes if the climate system warms more than median estimates. To do this, ambitious emissions reductions need to go hand in hand with scaled and environmentally sustainable carbon dioxide removal technologies. A ‘preventive capacity’ of several hundred gigatons of net removals might be required.
“There’s no way to rule out the need for large amounts of net negative emissions capabilities, so we really need to minimize our residual emissions. We cannot squander carbon dioxide removal on offsetting emissions we have the ability to avoid,” commented study coauthor Gaurav Ganti, research assistant at IIASA and a research analyst at Climate Analytics.
“Our work reinforces the urgency of governments acting to reduce our emissions now, and not later down the line. The race to net zero needs to be seen for what it is – a sprint,” Schleussner concludes.
Reference: “Overconfidence in climate overshoot” by Carl-Friedrich Schleussner, Gaurav Ganti, Quentin Lejeune, Biqing Zhu, Peter Pfleiderer, Ruben Prütz, Philippe Ciais, Thomas L. Frölicher, Sabine Fuss, Thomas Gasser, Matthew J. Gidden, Chahan M. Kropf, Fabrice Lacroix, Robin Lamboll, Rosanne Martyr, Fabien Maussion, Jamie W. McCaughey, Malte Meinshausen, Matthias Mengel, Zebedee Nicholls, Yann Quilcaille, Benjamin Sanderson, Sonia I. Seneviratne, Jana Sillmann, Christopher J. Smith, Norman J. Steinert, Emily Theokritoff, Rachel Warren, Jeff Price and Joeri Rogelj, 9 October 2024, Nature.
DOI: 10.1038/s41586-024-08020-9