Guest Post By Bob Tisdale
For the past few years, we’ve been showing in numerous blog posts that the observed multidecadal variations in sea surface temperatures of the North Atlantic (known as the Atlantic Multidecadal Oscillation) are not represented by the forced components of the climate models stored in the CMIP5 archive (which were used by the IPCC for their 5th Assessment Report). We’ve done this by using the Trenberth and Shea (2006) method of determining the Atlantic Multidecadal Oscillation, in which global sea surface temperature anomalies (60S-60N) are subtracted from the sea surface temperature anomalies of the North Atlantic (0-60N, 80W-0). As shown in Figure 1, sea surface temperature data show multidecadal variations in the North Atlantic above and beyond those of the global data, while the climate model outputs, represented by the multi-model mean of the models stored in the CMIP5 archive, do not. (See the post here regarding the use of the multi-model mean.) We’ll continue to use the North Atlantic as an example throughout this post for simplicity sake.
Figure 1 (Figure 3 from the post Questions the Media Should Be Asking the IPCC – The Hiatus in Warming.)
Michael Mann and associates have attempted to revise the definition of multidecadal variability in their new paper Steinman et al. (2015) Atlantic and Pacific multidecadal oscillations and Northern Hemisphere temperatures. Michael Mann goes on to describe their efforts in the RealClimate post Climate Oscillations and the Global Warming Faux Pause. There Mann writes:
We propose and test an alternative method for identifying these oscillations, which makes use of the climate simulations used in the most recent IPCC report (the so-called “CMIP5” simulations). These simulations are used to estimate the component of temperature changes due to increasing greenhouse gas concentrations and other human impacts plus the effects of volcanic eruptions and observed changes in solar output. When all those influences are removed, the only thing remaining should be internal oscillations. We show that our method gives the correct answer when tested with climate model simulations.
It appears their grand assumption is that the outputs of the climate models stored in the CMIP5 archive can be used as a reference for how surface temperatures should actually have warmed…when, as shown as an example in Figure 1, climate models show no skill at being able to simulate the multidecadal variability of North Atlantic. (There are posts linked at the end of this article that show climate models are not capable of simulating sea surface temperatures over multidecadal time frames, including the satellite era.)
Let’s take a different look at what Steinman et al. have done. Figure 2 compares the model and observed sea surface temperature anomalies of the North Atlantic for the period of 1880 to 2014. The data are represented by the NOAA ERSST.v3b dataset, and the models are represented by the multi-model mean of the climate models stored in the CMIP5 archive. Both the model outputs and the sea surface temperature data have been smoothed with 121-month filters, the same filtering used by NOAA for their AMO data.
As illustrated, the data indicate the surfaces of the North Atlantic are capable of warming and cooling at rates that are very different over multidecadal periods than the forced component of the climate models. The forced component is represented by the multi-model mean. (Once again, see the post here about the use of the multi-model mean.) In fact, the surfaces of the North Atlantic warmed from about 1910 to about 1940 at a rate that was much higher than hindcast by the models. They then cooled from about 1940 to the mid-1970s at a rate that was very different than the models. Not too surprisingly, as a result of their programming, the models then align much better during the period after the mid-1970s.
Steinman et al., according to Mann’s blog post, have subtracted the models from the data. This assumes that all of the warming since the mid-1970s is caused by the forcings used to drive the climate models. That’s a monumental assumption when the data have indicated the surfaces of the North Atlantic are capable of warming at rates that are much higher than the forced component on the models. In other words, they’re assuming that the North Atlantic since the mid-1970s has not once again warmed at a rate that is much higher than forced by manmade greenhouse gases.
What Steiman et al. have done is similar to subtracting an exponential curve from a sine wave…where the upswing in the exponential curve aligns with the last minimum to maximum of the sine wave…without first establishing a relationship between the two totally different curves.
MICHAEL MANN PRESENTED A CLEAR INDICATION OF HOW POORLY CLIMATE MODELS SIMULATE MULTIDECADAL SURFACE TEMPERATURE VARIABILITY
I had to laugh when I saw the following illustration presented in Michael Mann’s blog post at RealClimate. I assume it’s from Steinman et al. In it, the simulations of the surface temperatures (represented by the multi-model mean of CMIP5-archived models) of the North Atlantic, North Pacific and Northern Hemisphere surface temperatures have been subtracted from the data. That illustration clearly shows that the climate models in the CMIP5 archive are not capable of simulating the multidecadal variations in the sea surface temperatures of the North Atlantic and the North Pacific or the surface temperatures of the Northern Hemisphere.
In other words, that illustration presents model failings.
If we were to invert those curves, by subtracting reality (data) from computer-aided speculation (models), the resulting differences would show how greatly the models have overestimated the warming of the North Pacific and Northern Hemisphere in recent years.
What were they thinking? We’d let that go by without calling it to everyone’s attention?
Thank you, Michael Mann and Steinman et al (2015). You’ve made my day.
We’ve illustrated and discussed how poorly climate models simulate sea surface temperatures in the posts:
- Alarmists Bizarrely Claim “Just what AGW predicts” about the Record High Global Sea Surface Temperatures in 2014
- IPCC Still Delusional about Carbon Dioxide
For more information on the Atlantic Multidecadal Oscillation, refer to the NOAA Frequently Asked Questions About the Atlantic Multidecadal Oscillation (AMO) webpage and the posts:
- An Introduction To ENSO, AMO, and PDO — Part 2
- Multidecadal Variations and Sea Surface Temperature Reconstructions
Some readers might think that Steinman et al. is nothing more than misdirection, a.k.a. smoke and mirrors. What do you think?
Thanks to blogger “Alec aka Daffy Duck” for the heads-up.