Here is the second post summarizing some of the climate change research I did at CEA last summer (the first is here). Below are links to outlines of the reasoning behind a few of the estimates there (they are the ‘structured cases’ mentioned in the GWWC post).
The organizations were investigated to very different levels of detail. This is why Sandbag for instance comes out looking quite cost effective, but is not the recommendation. I basically laid out the argument they gave, but had almost no time to investigate it. Adding details to such estimates seems to reliably worsen their apparent cost-effectiveness a lot, so it is not very surprising if something looks very cost effective at first glance.
The Cool Earth case is the most detailed, though most of the details are rough guesses at much more detailed things. The cases are designed to allow easy amendment if more details or angles on the same details are forthcoming.
As a side note, I don’t think GWWC plans on more climate change research soon, but if anyone else is interested in such research, I’d be happy to hand over some useful (and neatly organized!) bits and pieces.