A few more things I’m going to add …
It’s wrong. As I noted in that post, it’s not a credible chart that’s being “tossed around” anywhere but in denialist circles; it comes from Bjorn Lomborg, who is a shill for the fossil fuel industry and who’s been convicted in Denmark of scientific dishonesty with regard to some of his claims about climate change.
ETA: And note that I linked over here to an excellent debunking of the bullshit arguments that Trump is making.
With regard to the Paris accord, the question is malformed; in essence, the question is backwards. The agreement is primarily drafted in terms of outcomes [you may have to click on “The Paris Agreement” on the left-hand side to go the right section], the most important of which is to limit further temperature rise to well below 2°C and to make every effort to limit it to 1.5°C. A secondary goal is for emissions to peak ASAP and thereafter stabilize and decline, with zero net new emissions in the second half of this century.
So “the effects of the Paris accord” are self-evidently defined in the agreement itself, and it can be said that the temperature goals are consistent with scientific evidence of dangerous thresholds and damaging impacts, and the emissions goals are broadly consistent with the temperature goals according to current understanding of climate sensitivity.
There is a real and valid criticism that can be made of the Paris accords, but it isn’t the kind of nonsense that Lomborg is spouting, and it’s particularly not what conservatives want to hear. The criticism is that the goals for net emissions reductions are not sufficiently binding and probably not aggressive enough. A quick look at this graph tells the story. The four RCPs represent the net new forcing from atmospheric carbon in 2100, in watts/m[sup]2[/sup]. RCP 2.6 is generally considered an unrealistically aggressive mitigation scenario, RCP 8.5 is business as usual (i.e.- Trump policy), and the middle two are generally considered the realistic ones. The trouble is, it will take something close to RCP 2.6 to achieve the desired temperature outcome by 2100 and keep temperature rise below dangerous thresholds.
This research paper and this one [PDF] both point to similar conclusions. The first paper questions whether 1.5°C is achievable without substantially more aggressive policies; the second one goes further and concludes that “the 2°C threshold could be avoided only if net zero greenhouse gas emissions (GHGEs) are achieved by 2085 and late century negative emissions are considerably in excess of those assumed in Representative Concentration Pathway (RCP) 2.6”. This is perhaps somewhat of an outlier but not greatly so, and certainly plausible.
The question that Americans should be asking is this: if we are already at the point that it may take the most optimistic and aggressive mitigation policies to bring climate change safely under control, isn’t doing nothing – and indeed mining for more coal and trying to grow fossil fuel use – the most reckless and stupid policy imaginable? Doesn’t it underscore the vital importance of a concerted global effort to meet or exceed the Paris objectives, starting immediately?
