The 1.5-degree limit of the Paris Climate Agreement is getting closer. Hope is increasingly placed on temporarily exceeding 1.5 degrees, after which we can bring the temperature down again through large-scale CO2 removal. The risks of such an overshoot are underestimated, a large team of researchers argues. They also question its feasibility.

Underestimated Risks 

Even temporary warming leads to lasting effects on the climate, ecosystems, and human societies. The higher the peak in warming, the more extreme weather events, such as heat, precipitation, and drought, will manifest. The melting of ice caps, and thus sea level rise, will also accelerate the longer we remain above 1.5 degrees of warming. The researchers also warn against overestimating confidence in future CO₂ removal. 

The Risk of Tipping Points Increases Above 1.5 Degrees of Warming 

Moreover, the risk of exceeding tipping points increases the longer and higher the warming exceeds 1.5 degrees. Tipping points are abrupt changes, where (a part of) the climate system becomes unstable and enters a new equilibrium state. Often these changes are irreversible on human timescales. 

With each exceedance of 1.5 degrees of warming, the risk of tipping points increases (see Figure 1). Even if the warming is brought back down to 1.5 degrees after a peak through large-scale CO2 removal, this risk remains high. In this study, four tipping points are included: the instability of the AMOC, the Amazon, and the ice sheets of Greenland and Antarctica.