Risk of Tipping Points From Exceeding 1.5°C Can Be Minimized if Global Heating Quickly Reversed, Researchers Say

Current climate policies are putting the world at a high risk of critical Earth system components reaching tipping points, even if global temperatures return to less than 1.5 degrees Celsius above the pre-industrial average following a period of overshoot.

However, a new study has found that, if global heating is quickly reversed, these risks could be minimized.

The human-caused climate crisis has the potential to cause a destabilization of large-scale elements of Earth systems like ocean circulation patterns, ice sheets and components of the global biosphere. In the study, the researchers examined the risks that future emissions scenarios and current mitigation levels posed to four interconnected tipping elements, a press release from the International Institute for Applied Systems Analysis (IIASA) said.

The research team determined the risks of tipping for destabilizing a minimum of one of four central climate elements: the West Antarctic Ice Sheet, the Greenland Ice Sheet, the Amazon Rainforest and the Atlantic Meridional Overturning Circulation (AMOC) — the Atlantic Ocean’s main ocean current system. All four of these contribute to the regulation of the stability of the planet’s climate. Sudden changes to these biophysical systems can be triggered by global heating, leading to irreversible outcomes.

The report’s analysis explains how important it is to stick to the climate targets laid out in the Paris Agreement, while emphasizing that our current choices will impact the planet for centuries or even millennia.

“Our results show that to effectively limit tipping risks over the coming centuries and beyond, we must achieve and maintain net-zero greenhouse gas emissions. Following current policies this century would commit us to a high tipping risk of 45% by 2300, even if temperatures are brought back to below 1.5°C after a period of overshoot,” said Tessa Möller, co-lead author of the study and a researcher with the Potsdam Institute for Climate Impact Research (PIK)’s Integrated Climate Impacts Research Group, in the press release.

The researchers discovered that tipping risks become substantial by 2300 for several of the future emissions scenarios they assessed. If the average global temperature does not return to less than 1.5 degrees Celsius by 2100 — even if net-zero greenhouse gas emissions are reached — there will be a tipping risk of as much as 24 percent by 2300. This means that in roughly one-quarter of the scenarios that do not return to less than 1.5 degrees Celsius by the end of the century, a minimum of one of the tipping elements they considered will have tipped.

“We see an increase in tipping risk with every tenth of a degree of overshoot above 1.5°C. If we were to also surpass 2°C of global warming, tipping risks would escalate even more rapidly. This is very concerning as scenarios that follow currently implemented climate policies are estimated to result in about 2.6°C global warming by the end of this century,” said co-lead author Annika Ernest Högner, also with PIK, in the press release.

The study, “Achieving net zero greenhouse gas emissions critical to limit climate tipping risks,” was published in the journal Nature Communications.

“Only a swift warming reversal after overshoot can effectively limit tipping risks. This requires achieving at least net-zero greenhouse gases. Our study underscores that this global mitigation objective, enshrined in Article 4 of the Paris Agreement, is vital for planetary stability,” said Carl Schleussner, one of the authors of the study and a leader with the IIASA Integrated Climate Impacts Research Group, in the press release.

The research team said that the models currently being used to study Earth’s systems cannot yet fully capture the feedback loops, complex behaviors and interactions between some tipping elements. In order to address this issue, they used a more simple, stylized model that represented the tipping elements with four connected mathematical equations. This allowed them to consider future stabilizing interactions, such as the weakening AMOC’s cooling effect on the Northern Hemisphere.

“This analysis of tipping point risks adds further support to the conclusion that we are underestimating risks, and need to now recognize that the legally binding objective in the Paris Agreement of holding global warming to well below 2°C, in reality means limiting global warming to 1.5°C. Due to insufficient emission reductions, we run an ever increasing risk of a period of overshooting this temperature limit, which we need to minimize at all costs to reduce dire impacts to people across the world,” said PIK Director Johan Rockström, another co-author of the study, in the press release.