Is Global Warming Less than We Thought?
A discussion of a provocative new climate science paper
I noted on Twitter and Notes that it seems that discussion of topics generally in the purview of IPCC Working Group 1 ā the physical science of climate change ā seem to have dissipated in recent years. Iām not sure why that has happened, but it has motivated me to experiment here at The Honest Broker. I am of the view that science is stronger when discussed and challenged out in the open, and in that process we all get smarter.
Here is how this will work. This post introduces a new paper that I find interesting and which may or may not be significant in our understandings. I summarize it below and briefly give my views. I then invite discussion, experts especially, but all are welcome. For the first time I will open comments to everyone. There is one rule: Participate respectfully, politely and generously. If you donāt, youāll be removed from this forum without warning. With that, letās get to it!
Zou et al. 2023 is the paper I am inviting you to discuss (thanks @weerrecords!), which Iāll call Zetal23. It is open access and can be found at the link below.
Zou, C. Z., Xu, H., Hao, X., & Liu, Q. (2023). MidāTropospheric Layer Temperature Record Derived from Satellite Microwave Sounder Observations with Backward Merging Approach. Journal of Geophysical Research: Atmospheres, e2022JD037472.
The authors explain what they did in the study:
Long-term observations of global atmospheric temperatures from satellite microwave sounders play a vital role in climate change research. These observations involved multiple satellites spanning several decades. Careful intersatellite calibration and bias correction are needed to derive inter-consistent records from multi-satellite observations for reliable climate change detection. Here we develop a new version of the NOAA Center for Satellite Applications and Research (STAR) mid-tropospheric temperature (TMT) time series for climate trend investigation.
Long-timers in the climate space will know well that debates over satellite temperature trends used to be knock-down, drag-out affairs. In a wiseacre nutshell ā if you favored the satellite temperature record, you were probably a denier, and if you saw the satellites as flawed, then you were onsides. Here is how Carbon Brief characterized the debate back in 2017:
Climate sceptics have long claimed that satellite data shows global warming to be less pronounced than observational data collected on the Earthās surface.
The occasion for that characterization was a paper (Mears and Wentz 2017) that suggested that a leading satellite time series may have been flawed and as a result, underestimated warming trends. Carbon Brief explained at the time of the then-new paper:
Researchers from Remote Sensing Systems (RSS), based in California, have released a substantially revised version of their lower tropospheric temperature record. After correcting for problems caused by the decaying orbit of satellites, as well as other factors, they have produced a new record showing 36% faster warming since 1979 and nearly 140% faster (i.e. 2.4 times larger) warming since 1998. This is in comparison to the previous version 3 of the lower tropospheric temperature (TLT) data published in 2009.
Well, as I often warn, be careful celebrating the results of any one study too much, because science moves ahead and there is no guarantee that any single paper stands the test of time. And that brings us back to Zetal23 ā written by a highly qualified and well-published team of researchers from the National Oceanic and Atmospheric Administration (NOAA) and published in a leading climate science journal.
Zetal23 have produced a new estimate of global warming using satellites, which can be seen in the figure below.
They explain of the significance of the data in the figure:
The above TTT [Temperature Total Troposphere] trends have strong implications for trends in climate model simulations and other observations. Santer etĀ al.Ā (2021) reported that the multi-model averages for the TTT trends from CMIP5 and CMIP6 were 0.28ā0.29Ā K/decade during 1979ā2019. The total TTT trend found in this study was only one-half of the climate model simulations during the same period. This is consistent with conclusions in McKitrick and ChristyĀ (2020) for a slightly shorter period (1979ā2014). Possible reasons for the observation-model differences in trends may include climate model biases in responding to external forcings (McKitrick & Christy,Ā 2020), deficiencies in the post-millennium external forcings used in model simulations (Santer, Fyfe, etĀ al.,Ā 2017), phase mismatch in natural internal climate variability (Po-Chedley etĀ al.,Ā 2021; SuĆ”rez-GutiĆ©rrez etĀ al.,Ā 2017), and possible residual errors in satellite data sets.
Read that again, especially the last sentence. Zetal23 are suggesting the possibility that either observations of global warming are flawed, that climate models are flawed, or maybe both. These possibilities would ā if true ā be very scientifically important. Hence, why discussion of Zetal23 is important.
My two cents:
Nothing in the Zetal23 has any implications for my views of climate policy, which remain highly robust to the evolution of scientific understandings, uncertainties and ignorance, as they should be.
The new study adds weight to an analysis I participated in in 2009 that offered āAn alternative explanation for differential temperature trends at the surface and in the lower troposphere,ā (which, by the way, was published in the same journal as Zetal23) in which we hypothesized that there was a warm bias in the land surface temperature record as compared to the satellite temperature record due to real-world physical processes in the atmospheric boundary layer. The paper started as a ādinner tableā debate between my dad and I ā you can read all about it in non-technical language here and a more technical discussion here.
With that, I invite you to join a discussion of Zetal23.
Is it sound? If so, is it important?
I appreciate your support. I am embarking on an experiment to see if a new type of scholarship is possible. I am looking to make a break from traditional academia and its many pathologies, and this Substack is how Iām trying to make that break. I am well on my way. Please consider a subscription at any level, and sharing is most appreciated. Independent expert voices are going to be a key part of our media ecosystem going forward and I am thrilled to be playing a part. You make that possible.
FYI, my Dad will have a post shortly on ocean heat content as a better metric of global warming than atmospheric temperatures ... stay tuned
I became an Expert Reviewer for AR6 wg1 partly because of this issue. I had written a paper for my Masters (in climate science and policy) referring to Christy and McNiderās paper āSatellite Bulk Tropospheric Temperatures as a Metric for Climate Sensitivityā Asia-Pac. J. Atmos. Sci., 53(4), 1-8, 2017, DOI:10.1007/s13143-017-0070-zā which showed the lack of warming in the upper troposphere ā the āmissing hotspot.ā Dr Christy had alerted me to observational charts published by the IPCC in AR5 as āsupplementalā material, months after the publication of the main report and the had story moved on (see figure 10.SM.1 from Chapter 10SM). These charts show a divergence between observations and modelled upper tropospheric warming. But the IPCCās conclusion was that the models were probably correct and the problem lay with the satellites. Greenhouse warming should be most obvious in areas of the atmosphere with low water vapour ā the upper troposphere and the North and South poles. Only the North pole shows conclusive evidence of warming.
My paper started as a simple energy budget review so I looked at the surface temperature record ā specifically as covered by AR5 p.189. I went through the papers cited and was concerned to find they were not properly summarised. For example, Zhang et al 2010 found nearly a third of observed warming across China was attributable to UHI. But the IPCC only reported the study āfound no evidence for urban influences in the desert North West region of China despite rapid urbanization.ā This secondary finding was due to artificial oases, an explanation not included by the IPCC. I contacted Dr Ren, a co-author who had submitted expert comments in the Second Order Draft advocating for Zhang et alās primary finding (which was stated as 'accepted'). Dr Ren considered that the language used was likely part of a predetermined decision on the issue.
I also looked at the comments to Chapter two, SOD, page 189 and saw there was considerable debate about what should be included and a divergence of views ā 10 pages worth. Dr Phil Jones of the CRU, the lead author for AR4, contributes vociferously. Dr Ren submits as well as the likes of Christy and others arguing for higher levels of uncertainty.
The following comment was from Marcel Crok, The Netherlands, was accepted: āYou should mention Fall, S., D. Niyogi, A. Gluhovsky, R. A. Pielke Sr., E. Kalnay, and G. Rochon, 2009: Impacts of land use land cover on temperature trends over the continental United States: Assessment using the North American Regional Reanalysis. Int. J. Climatol., 10.1002/joc.1996. [Fall et al 2010] This paper shows that most of the trends in the US can be explained by land use changes. In their words: "As most of the warming trends that we identify can be explained on the basis of LULC changes, we suggest that in addition to considering the greenhouse gases-driven radiative forcings, multi-decadal and longer climate models simulations must further include LULC changes."
This study was duly cited (top right of page 189) but the key conclusion, that LULC can account for most warming trends, was not reproduced ā rather the conclusion was modified to simply say their Reanalyses work matched observations. Rogerās Dad was a co-author, with Eugenia Kalnay, Jule Charneyās protĆ©gĆ© and a legend in the numerical weather prediction space. Kalnay and Cai 2004 had made a similar finding. But the IPCCās conclusion was that the surface record was likely within 10% of that observed (āhigh agreementā).
Needless to say I received a poor mark, the lowest in class, and a āsit down and talking toā by two IPCC scientists on the faculty.
I was pleased to advocate for the inclusion of John Cristyās conclusions in AR6 and to see that the IPCC modified their approach to now acknowledging, with medium confidence, that the upper troposphere observations are inconsistent to those modelled. They refused to address the shortcomings of their treatment of Fall et al 2010, saying it was out of scope for AR6.
Its good to see multiple study groups now agreeing with John, Roy and others. Hats off to their perseverance.