Instead of apocalyptic warnings about “immediate risk” a top line message of this report should be: Great News! The Extreme Scenario that IPCC Saw as Most Likely in 2013 is Now Judged Low Likelihood. I am actually floored that this incredible change in such a short time apparently hasn’t even been noticed, much less broadcast around the world.
For its part, the IPCC claims to be “neutral” with respect to scenario assumptions, despite also, seemingly contradictorily, identifying certain scenarios as low likelihood and others more in line with current policies. Here is where the IPCC gets into some trouble.
Despite acknowledging the low likelihood of the most extreme scenarios RCP8.5 and SSP5-8.5, which were the dominant focus of the 2013 IPCC report, the extreme scenarios dominate the current report as well.
The phrase “extreme scenario” might be a little difficult to understand in the abstract. So let me explain what an extreme scenario looks like, and why it is obviously, undeniably implausible. All of RCP8.5, SSP5-8.5 and SSP3-7.0 assume that the world is going to massively increase consumption of coal in the future. The scenarios project that we will replace natural gas with coal, we will replace nuclear with coal, we will replace wind and solar, we will even chose to abandon gasoline for cars and use coal-to-liquid as fuel. If that sound ridiculous — it is!