I've discussed concerns I have about the Berkeley Earth Project's attempt (BEST) to construct a global temperature record here a couple times. One time I wrote a post discussing how, according to BEST, the state of Illinois is so terrible at measuring temperatures it needs to have its measurements warmed by about one degree per century.
Another time I highlighted the fact BEST's changes to individual stations are based upon perceived differences so small one can barely see them if they're plotted. As I said then, I think the way BEST changes to these stations reflect nothing more than them over-fitting their data.
Today I'd like to highlight an issue which combines both of those problems.
For a bit of an introduction, I recently looked at the gridded data BEST published showing its estimates of average, monthly temperatures across the globe (available on this page). After some playing around, I decided to extract the values given for the area I live. I then did the same thing with another temperature record, NASA's GISS (available on this page).
The values aren't completely comparable as the GISS data set covers a shorter period. GISS also uses larger grid sizes. Still, I thought it'd be interesting to compare them. To keep things simple, I graphed data from both data set only for the period of overlap. This is what I got (with a five year smooth):
I'm not sure anything more needs to be said. In case I'm wrong, and the issue isn't obvious, I'll plot the same graphs, but this time I'll include trend lines:
It's amazing. From month to month and year to year, GISS and BEST look nearly identical. The high frenquency components of their graphs are indistinguishable. The only meaningful differences between the GISS and BEST estimates for my area is BEST adds a huge warming trend.
To be clear, I don't think this means BEST is fraudulently adjusting the data. I'm not Steven Goddard. I suspect what's actually happening is BEST is smearing warming from other areas into mine. That is, warming in other states is causing Illinois to seem like it's warming far more than it actually is. That's not fraud. That's just low resolution in the estimates.
But here's the thing. BEST is supposed to be the best temperature record. It has a website encouraging people to look at data on as fine a scale as individual cities. WHY?! If BEST can't come close to getting things right for the state of Illinois, why should anyone care at what it says about the city of Springfield, Illinois?
At what scale does BEST stop giving imaginary results and start getting a right answer? It doesn't at the city level. It doesn't at the state level. What about at the regional level? Could it get temperatures right for something like, say, Southeast United States? Nope.
We can't pick areas much larger than that. The Southeast United States is about half the size of Australia. It's about a third the size of Europe. If BEST can't get it right, how could it get Australia or Europe right? And that's ignoring the fact the Southeast United States has far more temperature stations (per area) than either of those!
I get almost everybody seems to agree BEST gets things right at the global scale, but couldn't we all agree there's a problem if BEST can't come close to the right answer when looking at entire continents?