Every 0.1°C of planetary warming increases the risk of reaching dangerous tipping points, says a new open-access article published in the journal Nature Communications. It illustrates why emissions must be scaled back immediately, without waiting for future carbon capture technologies, the authors stress.
A tipping point arises when the next increment of temperature rise caused by greenhouse gas emissions shifts the structure of one of the Earth’s natural systems, producing a cascade of climate impacts out of proportion to the emissions themselves.
The new analysis, by a team of 10 scientists based at leading universities and environmental research institutes in Germany, Austria, the United Kingdom, the United States, and Sweden, focuses on four tipping points:
• Two cryosphere subsystems, the Greenland Ice Sheet (GIS) and the West Antarctic Ice Sheet (WAIS);
• Large-scale oceanic and atmospheric circulation patterns such as the Atlantic Meridional Overturning Circulation (AMOC);
• Biosphere subsystems like the Amazon Rainforest (AMAZ).
“Our results show that only achieving and maintaining net-zero greenhouse gas emissions, associated with a long-term decline in global temperatures, effectively limits tipping risks over the coming centuries and beyond, in line with earlier studies,” the researchers write.
The say their findings “imply that stabilization of global temperatures at or around 1.5°C is insufficient to limit tipping risk in the long term.” Effectively minimizing that risk requires bringing global temperatures down to below 1°C above pre-industrial levels.
Climate scientists have long raised the alarm about rising temperatures pushing systems to tipping points that are not only irreversible but can also hasten further warming, or can elicit other negative outcomes like widespread biodiversity loss or substantial shifts in precipitation patterns.
Already, some increasingly disrupted natural systems—such as in the Antarctic, which is currently facing a near-record heatwave—are raising concerns about how those systems will fare as climate change advances.
While past studies have evaluated global warming’s impacts on tipping points, the researchers say most models don’t fully account for “the non-linear behaviour, feedback, and interactions between some of the tipping elements.” This study aims complement those earlier results with “fold-bifurcation models” that help account for tipping points’ feedback mechanisms.
The study compares how tipping points would be affected by 10 possible future emissions pathways, including one scenario that follows current climate policies until warming declines after 2100, and another that follows a “broad shift towards sustainable development.”
In the findings, the scenario that follows current policies until 2100 results in the highest overshoot temperature of 3.3°C above pre-industrial levels before it declines to 1.5°C. This was also the scenario with the highest tipping risk.
The lowest temperature outcome shows up in a scenario that initially overshoots to 1.67°C, but then brings temperatures down below pre-industrial levels after 2100 through “heavy CDR [carbon dioxide removal] deployment.” However, David McKay, who studies climate tipping points at the University of Exeter’s Global Systems Institute but was not involved in this study, told Carbon Brief the scenario that assumes the success of still-untried carbon dioxide removal technology may not be possible. There is considerable debate about whether CDR technology will work as promised, McKay noted.
The analysis shows that at temperatures lower than 2°C above pre-industrial levels, the risk of reaching a tipping point rises by 1%-1.5% with each 0.1°C increase above 1.5°C. Above 2.5°C, tipping point risk grows by 3% per 0.1°C increase.
“A global mean temperature increase of 1.5 °C is not ‘safe’ in terms of planetary stability but must be seen as an upper limit,” the authors conclude.
“Domestic policies to reduce emissions need to be adopted and implemented, not only pledged, and a more significant and urgent effort is needed to mitigate the risks associated with tipping elements.”
According to Carbon Brief, it was a scientist who was not involved in the study who told them that the research “underlines the need for urgent emission cuts now that do not assume substantial carbon dioxide removal later.”