Climate End Game

 

 A report from PNAS, Proceedings of the National Academy of Sciences (US), urges governments to take off the blinders and begin evaluating climate breakdown  from a worst case scenario.

Despite 30 y of efforts and some progress under the United Nations Framework Convention on Climate Change (UNFCCC) anthropogenic greenhouse gas (GHG) emissions continue to increase. Even without considering worst-case climate responses, the current trajectory puts the world on track for a temperature rise between 2.1 °C and 3.9 °C by 2100.

  
...Even if anthropogenic GHG emissions start to decline soon, this does not rule out high future GHG concentrations or extreme climate change, particularly beyond 2100. There are feedbacks in the carbon cycle and potential tipping points that could generate high GHG concentrations (14) that are often missing from models. Examples include Arctic permafrost thawing that releases methane and CO2 (15), carbon loss due to intense droughts and fires in the Amazon (16), and the apparent slowing of dampening feedbacks such as natural carbon sink capacity (17, 18). These are likely to not be proportional to warming, as is sometimes assumed. Instead, abrupt and/or irreversible changes may be triggered at a temperature threshold. Such changes are evident in Earth’s geological record, and their impacts cascaded across the coupled climate–ecological–social system (19). Particularly worrying is a “tipping cascade” in which multiple tipping elements interact in such a way that tipping one threshold increases the likelihood of tipping another (20). Temperature rise is crucially dependent on the overall dynamics of the Earth system, not just the anthropogenic emissions trajectory.
 
...There are even more uncertain feedbacks, which, in a very worst case, might amplify to an irreversible transition into a “Hothouse Earth” state (21) (although there may be negative feedbacks that help buffer the Earth system). In particular, poorly understood cloud feedbacks might trigger sudden and irreversible global warming (22). Such effects remain underexplored and largely speculative “unknown unknowns” that are still being discovered. For instance, recent simulations suggest that stratocumulus cloud decks might abruptly be lost at CO2 concentrations that could be approached by the end of the century, causing an additional ∼8 °C global warming (23). Large uncertainties about dangerous surprises are reasons to prioritize rather than neglect them.

Comment Response -

Hi, TB.

I want to imagine that, if we looked at the bigger picture, these issues wouldn't seem so bleak. Then, when you zoom out, you see the full measure of what confronts us. Global heating presents what could become an existential calamity but so too does every other manifestation of humanity's inability or unwillingness to conform to the finite limits of our biosphere.

Our failure is manifest in how we take all of these threats and try to make them conform to political solutions that vary from nation to nation.

Comments response:

I agree, NPoV, that, even if the US and Russia were able to avoid a nuclear confrontation, a peer-on-peer war in our planet's fragile state would greatly worsen all the other existential threats we face. Yet I just read an op-ed in The Hill arguing that, unless Biden intervenes directly in Ukraine, America will be ensnared in yet another war without end.  The logic is so typical and perverse.

The wheels are coming off and the wagon is wobbly.