Judith Curry is an eminent scientist and a skeptic. Most of the discussion in this posting, comes from her blog Climate, ETC., titled: “The climate ‘crisis’ isn’t what it used to be”.
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:
- NYTimes David Wallace-Wells: Beyond catastrophe: A new climate reality is coming into view.
- WSJ: Good climate change news is fit to print. Slowly its percolating into the journalistic mind that recent research is upbeat
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.
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
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.
*AR stands for Assessment Report. These are based upon the content in the Intergovernmental Panel on Climate Change (IPCC) full reports, assembled by working groups. AR6 is the most recent report. The reputation of the ARs is in dispute. The full report, the 6th, is condensed to an AR6. The dispute is that many nonscientific personnel, such as delegates from industry, NGOs, etc. can force change that make the AR inconsistent with the full report.