I have not looked into the paper you mentioned in the original post, but I wrote about the one linked by Sanjay here. For reference:
Their [McKayâs tipping points] most extreme (maximum for positive, or minimum for negative) impact on the global temperature is descrived inTable S3 (see Supplementary Materials):
Lowlatitude Coral Reefs [die-off]: not defined (ND).
Boreal Permafrost [abrupt thaw]: ND.
Barents Sea Ice [abrupt loss]: ND.
Mountain Glaciers [loss]: 0.08.
Sahel & West African Monsoon [greening]: ND.
Boreal Forest [southern dieback]: â0.18.
Boreal Forest [northern expansion]: 0.14.
Boreal Permafrost [gradual thaw]: 0.7.
Arctic Summer Sea Ice [loss]: 0.25.
Global Land Carbon Sink [weaken]: ND.
Ocean Biological Pump [weaken]: ND.
Marine Methane Hydrates [dissociation]: 0.5.
Indian Summer Monsoon [shift]: ND.
South. Ocean Sea Ice [Ind. increase]: ND.
South. Ocean Sea Ice [Pac./âAtl. loss]: ND.
South. Ocean Sea Ice [bimodality]: ND.
Equatorial Stratocumulus Clouds [breakup]: 8.
Antarctic Bottom Water [collapse]: ND.
Indian Ocean Upwelling [abrupt increase]: ND.
Tibetan Plateau Snow [abrupt loss]: ND.
Ocean Deoxygen -ation [global anoxia]: ND.
Arctic Ozone Hole [abrupt expansion]: ND.
El Nino Southern Oscillation [permanent /â extreme]: ND.
Northern Polar Jet Stream [instability]: ND.
Adding up all of these, I get a maximum global warming of 10.37 ÂșC, which is mostly driven by the 8 ÂșC which could result from the breakup of the equatorial stratocumulus clouds.
So my very tentative conclusion was that the potential breakup of the equatorial stratocumulus clouds is an important consideration. I should note it is still unclear whether this tipping point actually exists, but uncertainty should push us towards acting as if it does exist (unless we expect lots of regression to the mean in further studies). McKay says:
However, this [breakup of the equatorial stratocumulus clouds] has only been resolved in one model so far, and so remains highly uncertain. If further research supports the existence of this tipping point, EQSC would constitute a global core tipping element, albeit one that is unlikely to triggered by anthropogenic warming unless global policy fails.
The part I highlighted above refers to the fact we need 1,200 ppm to trigger that tipping point. From the abstract of the paper which introduced it, Schneider 2019:
In the simulations, stratocumulus decks become unstable and break up into scattered clouds when CO2 levels rise above 1,200âppm.
Until reaching 1,200 ppm there would be quite some time to adapt. McKay says that concentration corresponds to âapprox. 6.3°C (7-8.9°C) at ECS of 3°C per 2xCO2â. However, I was impressed by how fast Schneider 2019 predicts the temperature transition (from 6 ÂșC of warming to 14 ÂșC (= 6 + 8) of warming) to be. I did not find information in the text, but there is a movie with a time series in the supplementary information. Here is the print of the cloud cover and temperature over time (sorry, I could not take a print without the play bar).
It looks like an increase of 6 ÂșC (= 303 â 297) happens in 20 days (= 275 â 255)! This is an underestimate, from the movie description:
The breakup of the stratocumulus clouds is more rapid than it would be in nature because of the unrealistically small thermal inertia of the underlying slab ocean.
That being said, even if the transition takes 10 times as long, 200 days is not much time. Nevertheless, overall, I am still pretty optimistic about extreme climate change (relative to other xrisks) given the low chance of 1,200 ppm.
Hi Johannes,
I have not looked into the paper you mentioned in the original post, but I wrote about the one linked by Sanjay here. For reference:
So my very tentative conclusion was that the potential breakup of the equatorial stratocumulus clouds is an important consideration. I should note it is still unclear whether this tipping point actually exists, but uncertainty should push us towards acting as if it does exist (unless we expect lots of regression to the mean in further studies). McKay says:
The part I highlighted above refers to the fact we need 1,200 ppm to trigger that tipping point. From the abstract of the paper which introduced it, Schneider 2019:
Until reaching 1,200 ppm there would be quite some time to adapt. McKay says that concentration corresponds to âapprox. 6.3°C (7-8.9°C) at ECS of 3°C per 2xCO2â. However, I was impressed by how fast Schneider 2019 predicts the temperature transition (from 6 ÂșC of warming to 14 ÂșC (= 6 + 8) of warming) to be. I did not find information in the text, but there is a movie with a time series in the supplementary information. Here is the print of the cloud cover and temperature over time (sorry, I could not take a print without the play bar).
It looks like an increase of 6 ÂșC (= 303 â 297) happens in 20 days (= 275 â 255)! This is an underestimate, from the movie description:
That being said, even if the transition takes 10 times as long, 200 days is not much time. Nevertheless, overall, I am still pretty optimistic about extreme climate change (relative to other xrisks) given the low chance of 1,200 ppm.