Projections for future levels of warming are calculated from “best guess” estimates around climate sensitivity. Climate sensitivity rests on some complex stuff, such as how changing cloud cover might affect the dynamics of warming. In essence, the lower that climate sensitivity is taken to be, the lower the expected level of warming.
That’s why there are broad bands of temperature range given in graphs that display possible future levels of warming.
Ken Caldeira and Patrick Brown (Nature) thought it would be good idea to figure out whether the higher or lower projections were more likely to be accurate. To do this they looked to see which models (high and low sensitivity) best matched recently measured observations(phys.org).
Models incorporating higher levels of climate sensitivity were more accurate at simulating recent and present climate observations. From that, Caldeira and Brown re-calculated that the chance of the world experiencing 4 degrees C of warming by the end of the century (at current emission rates) shifts from a 62% chance to a 93% chance. (The Independent) Put another way, we were telling ourselves we had a 3-1 chance of avoiding 4 degrees, and those odds have just dropped to about even money.
Obviously the work undertaken by Caldeira and Brown doesn’t touch on the fact that we’ve been “stacking” integrated assessment models by inserting things like negative emissions technology, and monkeying with emission rates and peak emission dates and what not to make our prospects look better than they actually are.
So we need to cut and cut fast. This link is going to bring back up a post that outlines a politically unpalatable, but as far as I can tell, perfectly feasible course of action that would allow us (at least, in NZ) to slaughter our emissions in a timely manner.
And just to finish I want to re-visit a short exchange with Rhinocrates last night. The suggestion was that even though we have landed ourselves with a square wheeled cart, we have no option but to get in behind and push in the hope we can transform our situation.
The problem I have with the notion that we’d make progress if everyone just “did their bit”, is simply that the economic, social and political paradigms that have brought us to this point, are the very ones that deny us the ability to do anything other than push a square wheeled cart into ever deeper ruts the ground.
If we want that cart shifted far enough and fast enough, we need to ‘walk’ it using levers (think “ice hockey sticks”) and anyone committed to ‘pushing’, is in the way and dangerous. So yeah, If you’re in behind and pushing, do your bit. Stop.