A new article from Proceedings of the National Academy of Sciences goes through eight climate change tipping points that have studied, and tries to assign an economic impact to each. I’ll list them here in order of highest to lowest impact according to this study (see Table 2). They use the change in social cost of carbon as their key metric.
Two tipping points have major potential impacts and represent over 80% of the total risk from the eight, according to this study:
- ocean methane hydrates
- permafrost carbon feedback
Four tipping points have relatively modest expected impacts, at least modest compared to the truly existential threats represented by the top two:
- West Antarctic Ice Sheet
- Greenland Ice Sheet disintegration
- Indian Summer Monsoon
- Amazon dieback
Finally, two actually have small positive impacts on the (human) economy according to these authors:
- Atlantic Meridional Overturning Circulation slowdown (AMOC)
- Arctic sea ice / Surface Albedo Feedback
They don’t include “nonmarket effects”, so if you just feel that the death of the Amazon forest is profoundly sad, that is not reflected here. The authors are explicit about this so I guess it is okay.
These results are mismatched with my impressions, which are most likely driven by the amount of media coverage given to tipping points. I have probably read the most about ice sheets, the AMOC, and the Amazon, and these somewhat surprisingly do not make the top of the list. I feel like I have some basic grasp of the scientific concepts on each of these other than the methane hydrates. I understand why releasing massive amounts of methane would raise temperatures. I just don’t yet understand the feedback loop that would cause it to happen, whereas with the permafrost thawing it is pretty clear. Are the methane hydrates just frozen and expected to melt? I suppose in that case they are very similar to methane under the permafrost, with the difference being land and water. So the release of vast amounts of trapped methane is by far the biggest impact identified by this paper. For the most part though, the solutions to address any of these tipping points are going to be the same – drastic greenhouse gas emissions reductions and/or drastic geoengineering. Nothing else is going to reduce the amount of heat and solar energy melting ice, thawing permafrost and undersea frozen methane hydrates, and affecting ocean currents across vast chunks of the planet.