Reposted from Dr. Roy Spencer’s Blog
January 21st, 2021 by Roy W. Spencer, Ph. D.
As part of my Jan. 19 presentation for Friends of Science about there being no climate emergency, I also examined surface temperature in Canada to see how much warming there has been compared to climate models.
Canada has huge year-to-year variability in temperatures due to its strong continental climate. So, to examine how observed surface temperature trends compare to climate model simulations, you need many of those simulations, each of which exhibits its own large variability.
I examined the most recent 30-year period (1991-2020), using a total of 108 CMIP5 simulations from approximately 20 different climate models, and computed land-surface trends over the latitude bounds of 51N to 70N, and longitude bounds 60W to 130W, which approximately covers Canada. For observations, I used the same lat/lon bounds and the CRUTem5 dataset, which is heavily relied upon by the UN IPCC and world governments. All data were downloaded from the KNMI Climate Explorer.
First let’s examine the annual average temperature departures from the 1981-2010 average, for the average of the 108 model simulations compared to the observations. We see that Canada has been warming at only 50% the rate of the average of the CMIP5 models; the linear trends are +0.23 C/decade and +0.49 C/decade, respectively. Note that in 7 of the last 8 years, the observations have been below the average of the models.
Next, I show the individual models’ trends compared to the observed trends, with a histogram of the ranked values from the least warming to the most warming, 1991-2020.
Note that the 93.5% of the model simulations have warmer temperature trends than the observations exhibit.
These results from Canada are generally consistent with the results I have found in the Midwest U.S. in the summertime, where the CMIP5 models warm, on average, 4 times faster than the observations (since 1970), and 6 times faster in a limited number of the newer CMIP6 model simulations.
Implications
The Paris Climate Accords, among other national and international efforts to reduce greenhouse gas emissions, assume warming estimates which are approximately the average of the various climate models. Thus, these results impact directly on those proposed energy policy decisions.
As you might be aware, proponents of those climate models often emphasize the general agreement between the models and observations over a long period of time, say since 1900.
But this is misleading.
We would expect little anthropogenic global warming signal to emerge from the noise of natural climate variability until (approximately) the 1980s. This is for 2 reasons: There was little CO2 emitted up through the 1970s, and even as the emissions rose after the 1940s the cooling effect of anthropogenic SO2 emissions was canceling out much of that warming. This is widely agreed to by climate modelers as well.
Thus, to really get a good signal of global warming — in both observations and models — we should be examining temperature trends since approximately the 1980s. That is, only in the decades since the 1980s should we be seeing a robust signal of anthropogenic warming against the background of natural variability, and without the confusion (and uncertainty) in large SO2 emissions in the mid-20th century.
And as each year passes now, the warming signal should grow slightly stronger.
I continue to contend that climate models are now producing at least twice as much warming as they should, probably due to an equilibrium climate sensitivity which is about 2X too high in the climate models. Given that the average CMIP6 climate sensitivity is even larger than in CMIP5 — approaching 4 deg. C — it will be interesting to see if the divergence between models and observations (which began around the turn of the century) will continue into the future.
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