The Trump Administration scored an own goal by its Cunning Plan to release the mandated National Climate Assessment on the Friday after US Thanksgiving, counting on comatose satiety to distract public attention. In fact, it was such a quiet news day, without outrageous Trump tweets, that the report’s dire warnings got unusual coverage.
The usual shills, rallied by the Leader himself, promptly decried the report as the usual alarmism.
For once, I have to say that the shills have half, or perhaps a quarter, of a point. The NCA makes the situation worse than it really is (which is bad enough). Here’s my take.
The issue lies in the use of a piece of professional jargon, the RCPs (Representative Concentration Pathways). These were defined ten years ago in 2008-2009 by the climate science community to provide benchmarks for comparing different climate models, using a short list of different assumptions about future emissions. RCP 8.5 is the highest emission track, leading to at least 4 degrees C of warming by end century. The best, RCP 2.6, represents early peaking of emissions and the prospect of climate stabilisation.
It matters a great deal which we are on. The NCA says it’s RCP 8.5. Overview (pdf page 10), my emphasis:
The higher scenario (RCP 8.5) represents a future where annual greenhouse gas emissions increase significantly throughout the 21st century before leveling off by 2100, whereas the other RCPs represent more rapid and substantial mitigation by mid-century, with greater reductions thereafter. Current trends in annual greenhouse gas emissions, globally, are consistent with RCP 8.5.
But wait, the full Chapter 2 on climate science, box 2.4, is more nuanced (references omitted):
Which scenario is more likely? The observed acceleration in carbon emissions over the past 15–20 years has been consistent with the higher future scenarios (such as RCP 8.5) considered in this assessment. Since 2014, however, the growth in emission rates of carbon dioxide has begun to slow as economic growth has become less carbon-intensive with the trend in 2016 estimated at near zero. Preliminary data for 2017, however, indicate growth in carbon emissions once again. These latest results highlight how separating systemic change due to decarbonization from short-term variability that is often affected by economic changes remains difficult.
Well, which is it? Continue Reading…