by Judith Curry
Growing realization by the climate establishment that the threat of future warming has been cut in half over the past 5 years.
Summary: The climate “catastrophe” isn’t what it used to be. Circa 2013 with publication of the IPCC AR5 Report, RCP8.5 was regarded as the business-as-usual emissions scenario, with expected warming of 4 to 5 oC by 2100. Now there is growing acceptance that RCP8.5 is implausible, and RCP4.5 is arguably the current business-as-usual emissions scenario. Only a few years ago, an emissions trajectory that followed RCP4.5 with 2 to 3 oC warming was regarded as climate policy success. As limiting warming to 2 oC seems to be in reach (now deemed to be the “threshold of catastrophe”),[i] the goal posts were moved in 2018 to reduce the warming target to 1.5 oC. Climate catastrophe rhetoric now seems linked to extreme weather events, most of which are difficult to identify any role for human-caused climate change in increasing either their intensity or frequency.
The main stream media is currently awash with articles from prominent journalists on how the global warming threat less than we thought. Here are some prominent articles:
David Wallace-Wells is one of the most interesting journalists writing in the climate space. In 2017, he wrote a 2017 New York Magazine article titled “The Uninhabitable Earth”, with subtitle: “Famine, economic collapse, a sun that cooks us: What climate change could wreak—sooner than you think.” Not long after publication of his book in 2019 entitled The Uninhabitable Earth, David Wallace-Wells made this statement: “Anyone, including me, who has built their understanding on what level of warming is likely this century on that RCP8.5 scenario should probably revise that understanding in a less alarmist direction.” DWW scores HUGE number of points with me for quickly adjusting his priors with the growing amount evidence that RCP8.5 is implausible.
Well, the “messaging” around DWW’s latest article is that we are succeeding with reducing emissions (no we are not). The second message is to acknowledge that that warming will be less than we thought, but the impacts of the warming will be worse than we thought (nope). The third message is that advances in science have brought us to this (relatively) happy place (nope)
At the heart of this good news is abandonment of RCP8.5 from UNFCCC policy making. The hero of science behind this abandonment is Justin Ritchie, a recent Ph.D. graduate (whose work has been cited in previous RCP8.5 posts at Climate Etc).
The COP26 and now the COP27 have quietly dropped RCP8.5 (and SSP5-8.5) from their considerations, focusing on the envelope between RCP4.5 and RCP2.6. The grand poohbahs of the IPCC apparently didn’t see this coming (or preferred to keep spinning the alarm), since they instructed climate modelers for CMIP6 to continue a focus on SSP5-8.5, and climate researchers continue to focus on this scenario in their impacts publications. The IPCC AR6 prominently featured SSP5-8.5, although WGI did make this lukewarm statement
“In the scenario literature, the plausibility of the high emissions levels underlying scenarios such as RCP8.5 or SSP5–8.5 has been debated in light of recent developments in the energy sector.”
The second so-called scientific advance is lower values of climate sensitivity. The so-called advance is associated with the IPCC AR6 decision NOT to include values derived from climate models (which have dominated previous IPCC reports). They implicitly acknowledge that climate models are running too hot and that you can pretty much get whatever value of climate sensitivity that you want from a climate model (this has been blindingly obvious to me and many others for over a decade). The IPCC AR6 lowered the upper likely bound of ECS to 4.0oC (from 4.5oC previously); this further acts to reduce the amount of projected warming. The IPCC AR6 also raised the lower likely bound of ECS to 2.5oC (from 1.5oC). Raising the lower bound of ECS is on very shaky ground, as per the recent publication by Nic Lewis
The COP27 is working from a value of expected warming of 2.5oC by 2100. This is arguably still too high for several reasons. IPCC expert judgment dismissed values of climate sensitivity that are on the lower end (that should not have been dismissed as per Nic Lewis’ paper). Further, the IPCC projections do not adequately account for scenarios of future natural climate variability. See these recent posts:
In addition to an insufficient number of solar and volcanic scenarios, the climate models ignore most solar indirect effects, and the climate model treatment of multidecadal and longer internal variability associated with ocean circulations are inadequate. While in principle these factors could go either way in terms of warmer vs cooler, there are several reasons to think these natural factors are skewed towards cooler during the remainder of the 21st century:
- Baseline volcanic activity since 1850 has been unusually low
- Most solar researchers expect some sort of solar minimum in the mid to late 21st century
- Solar indirect effects are inadequately treated by climate models, which would act to amplify solar cooling
- A shift to the cold phase of the Atlantic Multidecadal Oscillation is expected in the next decade, which influences not only global temperatures but also Greenland mass balance and Arctic sea ice.
Once you include alternative scenarios of natural variability, temperature change by 2100 could easily be below 2oC and even 1.5oC. Recall that this warming is with reference to a baseline of 1850-1900; 1.1oC warming has already occurred.
David Wallace-Wells provides some “hope” for the climate alarmists with this sentence:
“It’s sadly apparent by now that scientists have underestimated, not overestimated, the impact of warming.”
I just don’t know what further to say here. The IPCC AR6 provides very meager fodder to support DWW’s statement. Apart from sea level rise, which is unambiguously associated with global warming, there is no prima facie reason that extreme weather events would worsen in a warming climate. Observational evidence, provided that you go back at least to 1900, shows that nearly all horrible, recent weather and climate disasters have precedents in the 20th century and hence “detection” is very challenging. Climate models are not fit-for-purpose to simulate extreme weather events, let alone to attribute them to human caused warming. We are then left with back-of-the-envelope simple thermodynamic calculations to infer worsening of extreme weather events, which ignores the overwhelmingly dominant role of atmospheric and oceanic circulations.
Think about the implications of assuming extreme weather and horrible impacts are highly sensitive to a 0.5oC temperature change. If so, this leads to the conclusion that the dominant climate factor is natural climate variability, with year-to-year swings of several tenths of a degree from El Nino and La Nina, a substantial volcanic eruption, and/or multidecadal ocean oscillations. The rationale for ignoring natural climate variability is based on the assumption that large amounts of fossil-fueled warming from climate model simulations spiked by RCP8.5 and high values of ECS will swamp natural climate variability. Cut the warming in half (or reduce even further), and you lose the rationale for ignoring natural climate variability.
So is all this a “victory” for climate science? I don’t think so. But I told you so . . .
And finally Bret Stephen’s article includes this all important figure. Are we to infer that warming causes fewer deaths (well there is a STRIKING correlation)? Well maybe, but the real cause of this decline is increasing wealth, increased warnings, and adaptation to weather and climate extremes.
Extreme weather and climate events are something that needs to be dealt with independently of the AGW issue. The world has always suffered from weather and climate extremes, and it always will; this will not change with further warming or with emissions reductions.
The policy implications of all this is enormous. Unfortunately I suspect that the COP27 will focus too much on emissions reductions (which aren’t working and wont impact the climate in any event), and not enough on supporting development and adaptation for developing countries and most importantly supporting development in Africa by allowing them to benefit from their fossil fuels (other than by selling them to Europe). With regards to the later, a shout out to Rose Mustiso’s recent Nature publication; Rose is my favorite African activist and thinker on this topic.