2022-10-25 Zeke Hausfather - passing 1.5C bad but not a tipping point

Zeke Hausfather (@hausfath): To elaborate, the world will likely pass 1.5C in the 2030s. This will be bad: impacts we see from climate change today will be notably worse.

But its not a climatic tipping point that makes additional warming inevitable, and we do the public a disservice when we frame it as such https://twitter.com/hausfath/status/1584940190946054144

Zeke Hausfather (@hausfath): Our models are broadly linear in terms of the relationship between cumulative warming and emissions. And while I'm cognizant of models imperfections and cautious of "unknown unknowns", I'm a lot more worried about those in a 2.5C-5C world than a 1.5C one. https://twitter.com/hausfath/status/1584943538403299335/photo/1

Zeke Hausfather (@hausfath): What I do worry about is the widespread misconception of 1.5C as a tipping point in the climate system, and that these views will lead to despair, despondency, and doomerism once we pass 1.5C. If we give up, we let the fossil fuel interests win.

Zeke Hausfather (@hausfath): Now is the time that we need to step up our efforts, not give into despair; if limiting warming to 1.5C is out of reach, lets try and keep it at 1.6C or 1.7C. Because ultimately every tenth of a degree matters in terms of the impacts on human and natural systems.

Zeke Hausfather (@hausfath): And there are some reasons for cautious hope. While 1.5C is pulling out of reach, in many ways its become a lot more likely that we can limit warming below 2C.

A decade ago we were heading for 4C+, today we are heading for ~2.6C, and we can bend that curve further down. https://twitter.com/hausfath/status/1584943545705582594/photo/1

Dr. Genevieve Guenther (@DoctorVive): @hausfath I really urge you to reconsider stating that we are heading for +/- 2.6 C with such unequivocal confidence. Agree totally that framing 1.5C as a tipping point is a problem, but so is suggesting that a 2.6C temperature rise is a scientific fact rather than a political possibility.

Zeke Hausfather (@hausfath): @DoctorVive A fair point, and something I try to bring up regularly. While a central outcome of 2.6C is consistent with current policies, its hard to rule out closer to 4C if we get unlucky with climate sensitivity or carbon cycle feedbacks: https://twitter.com/hausfath/status/1579917923530919936

Dr. Genevieve Guenther (@DoctorVive): @hausfath Thanks for hearing me.