Cato Working Paper No. 35 — How Well Has It Held Up? (Part 3)

Now I will come to the conclusion of this three-part series ad show you how well Michaels and Knappenberger’s Climate Models and Climate Reality: A Closer Look at a Lukewarming World has held up. Because if the trends indicating a gross overprediction in the IPCC CMIP-5 model runs, a slower warming and a smaller climate sensitivity, which are the Cato paper’s conclusions, are broken, then their conclusions are liable to be ill-founded as well, which means we could be right back at the IPCC’s median estimate of 3.0 deg C ECS (Equilibrium Climate Science) sensitivity---give or take 1.5 deg C.

First, let me show you a very recent graph presented by climate scientist Gavin Schmidt of NASA’s GISS:

Chart G: Global Mean Surface Temperature Anomalies from the 1908-1999 Mean. Anomaly measurements are in degrees C. The CMIP5 Ensemble used has not been blended according to the Hadley Centre’s HadCRUT4 method of accounting for land surface air temperatures and sea surface temperatures. The forcing-adjusted CMIP5 takes into account the updated (historical) forcings to date. The NASA GISS’s GISTemp plotted temperature rise is shown by the red line; the Hadley Centre’s HadCRUT4 by the blue line. Cowtan & Way’s plot and the NOAA NCEI plot are shown by the orange and pale blue lines respectively. The estimated 2017 GISTemp temperature plot and its uncertainty spread is courtesy Gavin Schmidt; the estimated HadCRUT4 plot and its uncertainty spread for 2017 are mine, based on the latest data available from the Hadley Centre website (accessed 11/07/2017). Nota bene that the upper end of this uncertainty spread is hidden by the GISTemp estimated temperature plot for 2017.

The above chart clearly shows that the original CMIP5 model ensemble clearly overpredicts the amount of warming observed; the forcing-adjusted ensemble, less so. The NOAA NCEI and HadCRUT4 temperature plots dip below the 2.5th percentile line of the original ensemble and the original ensemble mean is only hit by the GISTemp and Cowtan & Way temperature plots for 2016, the year of a particularly strong El Nino. The estimated temperatures for 2017 show a drop of approximately 0.09 deg C for both the GISTemp and HadCRUT4 plots.

Clearly, we still have an apparent overprediction problem here even though the planet’s mean temperature rise is no longer in the Pause. To check this we can simply do the same sort of trend runs that Michaels and Knappenberger did to indicate a slow rate of warming in their paper.

Chart H. The trends for the predicted annual average global surface air temperatures taken from Chart G for the CMPI5 ensemble (pale green, purple and pale blue lines), and for the Hadley Centre’s HadCRUT4 (blue line) and NASA GISS’s GISTemp (red line) observed global mean temperatures taken from their latest data for a blend of land and ice surface air temperatures and ocean sea surface temperatures. Observed temperatures for 2017 are estimated as explained under Chart G above. The trends were plotted for all years from 1975 through 2008; the trend lengths run from 10 years (2008-2017) to 43 years (1975-2017).

It appears that in the above chart the CMIP5 Ensemble trends are noticeably higher than for Figure 2 in Part 1. Only the Ensemble Mean trend for 26-year trend length, corresponding to 1992 the year after Mt. Pinatubo blew up, is anywhere close to equal to the Multiple Model-run Mean (MMM) trend shown in Figure 2, as checked in Chart D in Part 2.  The observed trends for longest trend lengths appear at about 0.18 deg C/dec, well below the 2.5th Percentile line at approximately 0.20. After the 37-year trend length, the Hadley and NASA GISS lines begin to diverge. But the shorter observed trend lines after the 26-year trend length---YIKES! They diverge, run an arc and fly above the 97th Percentile line, crashing through the roof! And this is the problem with using short trend lengths; Cato’s figures 2 and 3 exhibit their shorter trend lengths showing trends dropping progressively toward the bottom of the graph, falling into the subbasement.

The above graph shows the influence of the still-warmed global mean temperature(s) of 2017 coming 0.09 deg C off the El Niño-influenced peak temperature(s) in 2016. The trends for trend lengths shorter than 16 years also show the influence of the Pause---the longer into the Pause, the higher the trend. Trend lengths shorter than 10 years would show even higher trends approaching 0.85 deg C per decade.

The IPCC CMIP5 Model Ensemble still overpredicts the amount of surface warming as can also be clearly seen in Chart G. This is because the Ensemble does not take into account the blend of land and ice surface air temperatures and ocean sea surface temperatures reflected in the observed data, and because the forcings under the RCP 8.5 (also RCPs 6.0, 4.5 and 2.6) scenario post-2006 were higher than the observed historical forcings after that year. Apparently the historical forcings between 1992 and 2006 were also erroneous and had to be updated, as shown in Figure 4 of the Cowtan et al 2015 paper, “Robust comparison of climate models with observations using blended land air and ocean sea surface temperatures,” accessible here.

And now I will show you the trends for the up-to-date forcing-adjusted CMIP5 as shown in Chart G versus the trends from the observed data:

Chart I The trends for the predicted annual average global surface air temperatures taken from Chart G for the forcing-adjusted (supplied with updated historical forcings from 1992 to date) CMPI5 ensemble (pale green, purple and pale blue lines), and for the UK Met Office Hadley Centre’s HadCRUT4 (blue line) and NASA GISS’s GISTemp (red line) observed global mean temperatures taken from their latest data for a blend of land and ice surface air temperatures and ocean sea surface temperatures. Observed temperatures for 2017 are estimated as explained under Chart G above. The trends were plotted for all years from 1975 through 2008; the trend lengths run from 10 years (2008-2017) to 43 years (1975-2017).

The observed temperature trend plots are still low in the long-term trend lengths when compared to the Ensemble Mean, but this time they are within the 95-percent spread, i.e., at or above the 2.5th percentile line. One possible explanation for this is that this CMIP-5 model, as the original one, does not take into account the blend of ocean sea surface and land air surface temperatures. If it did, Chart G would have stated as such. As in Chart H, the observed trends start at 0.18 deg C / decade, there is a peak at the 26-year trend length, corresponding to 1992 the year after Mt. Pinatubo blew up, and after that the observed temperature trends swing in an arc and fly through the roof of the 97th Percentile line, indicative of the twin influences of the Pause and the 2016 El Niño heat spike which the climate is still in, despite the Pacific Ocean presently exhibiting a La Niña. One last interesting tidbit: the Ensemble Mean and the 97.5th Percentile lines converge at the 13-year trend length, a curious coincidence.

It should be emphasized that in both Charts H and I the observed temperature trends diverge after the 37-year trend length, with the 2017 NASA GISS line roughly exhibiting a trend of 0.20 deg C / decade and the UK Met HadCRUT4 roughly showing a trend of 0.15 deg C / decade, before both trend lines rocket skyward under the influence of both the 2016 El Niño heat spike and the 2002-2014 Pause.

The one thing the Cato got right was that the original and blended CMIP5 Model Ensembles with historical forcings to 2006 overpredicted the amount of warming compared to the amount already observed. Cowtan et al also noted this with the original Ensemble and they made a double comparison using 84 of the model runs: all surface air temperatures vs land surface air temperatures, and historical to 2006 then RCP 8.5 vs updated historical forcings and presented their findings in Figure 4 of their paper:

Chart J (Cowtan et al 2015 Figure 4):  “Comparison of 84 RCP8.5 simulations against HadCRUT4 observations (black), using either air temperatures (red line and shading) or blended temperatures using the HadCRUT4 method (blue line and shading). The shaded regions represent the 90% range (i.e., from 5% to 95%) of the model simulations, with the corresponding lines representing the multimodel mean. (a) Anomalies derived from the unmodified RCP8.5 results and (b) the results adjusted to include the effect of updated forcings from Schmidt et al. [2014]. Temperature anomalies are relative to 1961–1990.” The purple shading is the overlap between the red and blue shadings.

Please note in the above chart that the multiple model set of 84 simulations that had the best fit to the observed post-1991 (post-Pinatubo) temperatures was the set that was run with (a) updated blended temperature anomalies (HadCRUT4 method) and (b) updated forcings to 2013. The observed temperatures run through 2014. Neither the updated forcings nor the observed temperatures include the years 2015 through 2017 which have the El Niño warming spike that brought an end to the Pause.  For those years’ observed temperatures catching up to the mean multimodel prediction, even with all surface air temperatures, see Chart G at the top.

Now what does this mean for the Cato Working Paper No. 35? Despite the paper being correct about the CMIP5 Model Ensemble with its original forcings grossly overstating the predicted warming, it does not follow that the trend lines are levelling off toward zero or even 0.10 deg C / decade. If anything, it shows that taking trends that are shorter than 30 years and extrapolating a lower Charney / ECS climate sensitivity toward a doubling of CO2 from them is a fool’s errand and that the longer trend lengths with their observed trend values of about 0.18 deg C / decade are to be preferred in roughly predicting any future warming. And what was the lower sensitivity favored by the Cato paper? 2 degrees Celsius for a doubling of CO2, which is more than enough to bring on the coming global superstorms that would wreck our civilization. A higher sensitivity, say 3 degrees Celsius, is more likely given the observed longer-term trend values and would be even worse for us because the storms would arrive at a lower CO2 content, that is, sooner.

Furthermore, the difference in the surface warming versus the mid-troposphere warming is creating a higher heat gradient between the surface and the mid-troposphere, meaning that more water vapor is going up into the atmosphere, creating more clouds and weirder and more extreme weather in diverse places. After all, we do know our weather has gotten weirder and some climate scientists are on record stating that it has become more extreme.

Cato’s Working Paper No. 35 has not held up well at all.