The good news is that it is better written and with better diagrams — no more turgid prose and obscure diagrams that we’ve come to expect from the IPCC.
The other ‘good’ news is facetiously articulated by the Australian:
The bad news is of course best articulated by Al Gore [link], including a dig at President Trump.
Oliver Geden tweets:
“One of the major governance ‘innovations’ of
#COP21 – agreeing on a >3°C deal while putting a 1.5°C label on it.”
This tweet by Richard N. Haas, President of the Council on Foreign Relations, pretty much sums up the policy situation:
“Nothing suggests world will come close to meeting this goal on climate change. There is no US leadership, and the phrase “international community” is more rhetoric than reality. We’d better set aside $ for adaptation and accelerate R&D on geoengineering.”
I don’t see much in the way of new science or better ways of assessing uncertainty — same old, same old. Projections are based on the CMIP5 simulations. There are some more recent references cited in the ‘impacts’ chapter. Most of this addresses the difference between 1.5 and 2.0 C impacts, and also strategies for mitigation etc. The main issue is removing CO2 from the atmosphere, in the absence of being able to meet emissions targets.
The main climate science conclusion is that things would be a little better at 1.5C relative to 2C. For example:
“By 2100, global mean sea level rise is projected to be around 0.1 metre lower with global warming of 1.5°C compared to 2°C (medium confidence).” [0.1 m = 4 inches.]
- collapse of the West Antarctic Ice Sheet, possibly resulting in up to 2.5 m sea level rise as per the NOAA (2017) report (actually, the IPCC does not even make this case, they are predicting SLR of 1-2 feet). This extreme scenario, which would maybe justify all this, is regarded as extremely unlikely, and we are not presently on such a trajectory. In any event, if the WAIS collapses it is more likely to be due to the geothermal heat flux and volcanoes beneath the ice sheet. Recent research shows portions of the WAIS rising at a rate of 41 mm/yr, acting to protect the WAIS from collapse. MASSIVELY uncertain.
- species extinction. After alarming conclusions in AR4, the AR5 backtracked, and this new Report backtracks even further. What about the ocean – acidification and declining oxygen? Our understanding is in its infancy, but this needs to be looked at more.