The IPCC report I’ve most been looking forward to is from Working Group III, on mitigation. It looks like drafts of that report are already leaking — Reuters has a (poorly written) rundown.
From what I can tell through the muddy writing, the IPCC lays out a range of mitigation scenarios, which would run anywhere from 0.2 to 3.0 percent of global GDP:
The IPCC scenario of a 0.2 percent loss in GDP in 2030 is based on stabilising greenhouse gases at 650 parts per million (ppm) in the atmosphere by 2030, up from about 430 ppm now. …
UN “best estimates” show that might bring a temperature rise of 3.2-4.0 C (5.8-3.2 F) over pre-industrial times. Tighter curbs would cost ever more.
The most stringent scenario, costing 3 percent of GDP, would limit greenhouse gases to 445-535 ppm by 2030, inside a range likely to bring a 2-2.4 Celsius (3.6-4.3F) rise.
From what I understand, most serious climate activists want to shoot for 450ppm or below.
How to go about mitigation? The Reuters write-up says only this:
… easily achieved curbs include better use of fossil fuels, shifts to energies such as wind, solar or nuclear power and better management of forestry and farming.
Economic benefits in addition to energy savings include better health from less pollution, less damage to agriculture from acid rain and greater energy security by cutting imports.
I guess we’ll find out more soon.