WUWT has a post by Bob Tisdale, based on one of Tisdale’s own posts. The theme is that ocean heat content (OHC) hasn’t risen as fast as GISS model projections. Watts even says “we have a GISS miss by a country mile.” But Tisdale can only support his claim by using tricks to hide the incline. In fact he uses two of the favorite tricks of deniers. One is a clever, but hardly new, trick called “cherry picking.” The other is ridiculously simple: misrepresentation.
Here’s Tisdale’s “money graph”:
If you want an honest comparison of these observations with prediction, you can find it at RealClimate, which does so using this graph:
Notice that from 2003 to 2010, the observations are higher than prediction, then lower than prediction — but overall OHC (actually OHCA, ocean heat content anomaly) has been pretty close to its predicted values. But then, that’s the honest way to compare them, which of course is not acceptable in some quarters.
Why does Tisdale give such a different impression? First let’s expose the cherry-picking part. To make it look as though observation is out of whack with prediction, Tisdale starts with 2003. His justification is to call this the “Argo-era,” which he claims he chose because
According to it, ARGO floats have been in use since the early 1990s, but they had very limited use until the late 1990s. ARGO use began to rise then, and in 2003, ARGO-based temperature readings at depth became dominant. Based on that, I’ll use January 2003 as the start month for the “ARGO-era” in this post.
I don’t believe him.
Here’s the ocean heat content data from NODC (which he uses):
It’s annual averages of the quarterly data you can find here. The trend line in the RealClimate graph starts about 1993, so let’s take the data from 1993 to the present, fit a trend line, then plot the residuals to see how observations differ from that trend:
If you want to start at the highest residual, the cherriest cherry-pick, the one which gives the most dishonest impression of the trend, start with the point circled in red. My opinion: that’s why Tisdale chose 2003.
Now let’s look at the misrepresentation — specifically a blatant falsification of what the GISS prediction is. I don’t know exactly what the GISS model prediction for OHCA is, neither does Tisdale, he just “eyeballed” it from the RealClimate graph. But let’s look at what the prediction would be for a simple linear extrapolation. The RealClimate trend line starts about 1993, so let’s take the data from 1993 through 2002 and fit a straight line, then extend that line as a prediction through 2010. We’ll call it “prediction by extrapolation.” It guarantees that our prediction line will have the correct slope and intercept to match a true continuation of the trend. And it gives this:
But Tisdale didn’t do that. He chose a slope to match his “eyeball” estimate of the trend line in the RealClimate graph, but chose the intercept to match 2003. He even states “Note that I’ve shifted the data down so that it starts at zero in 2003.” Let’s call that the “Tisdale method” and compare it to the honest method when extrapolating the trend line:
Sorry, Bob. When you try to match a line’s slope, but then shift that line upward, choosing the intercept deliberately to make the prediction look as bad as possible, that’s dishonest.
It’s also one of the most common tricks that many denialists have used to “hide the incline.” That, and cherry-picking, just might be their favorites.