Despite plenty of indications that the Earth has gotten warmer—like melting glaciers and ecosystems that are shifting toward the poles—there are a number of climate skeptics who simply don't accept the temperature records produced by three different organizations (NASA, NOAA, and the CRU). Many of them pinned their hopes on physicist Richard Muller, who was also not convinced the professionals had gotten it right. But Muller did something about it, forming the Berkeley Earth project, and building a huge database of land temperature records.

Back in October, Muller dropped his findings in a rather unconventional location: an editorial in The Wall Street Journal. Despite the hype, the results were rather bland. He produced a temperature record that was nearly identical to that of the other organizations. But now, Muller is back for round two, and this time he has chosen the New York Times as an outlet for his climate musings.

As before, his team uses a different statistical method of reconstructing temperatures that works well with short records, taken at sites that were shut or moved. NASA, NOAA, and the CRU use methods that require long records, so they have to make adjustments to the data from sites that have shifted or gotten new equipment. This compensates for the fact that these changes will lead to discontinuities in the record. Since Berkeley Earth doesn't need the same length, it can just skip adjustments entirely: any record with a discontinuity is just split there, and treated as two records. The team has now also pushed its analysis back to almost 1750, adding a century to the land temperature records produced elsewhere.

Once again, the more recent results are all within the statistical noise of the three mainstream temperature records. For a century and a half, Berkeley Earth is telling us what we already know. The data from before 1750 comes with a full degree Celsius of error on either side of the value. It suggests that the climate was roughly even prior to industrial times, although with very significant short-term variability.

The authors ascribe this variability to the frequency of major volcanic eruptions, as these have a known cooling effect. That seems to have led them to consider attribution more generally. To do so, they use an incredibly simplistic approach: start with the baseline temperature, add volcanic eruptions, then add other climate forcings to see which one recapitulates the temperature curve. They conclude greenhouse gasses fit the best (and more or less rule out solar variations as major drivers), although they note that carbon dioxide is serving as a proxy for a variety of human-driven changes.

It's not exactly a sophisticated analysis, and others have reached the same conclusion using far more appropriate methods. Nevertheless, it's another indication that it's hard to make sense out of our current trends in climate without recognizing that the greenhouse effect is real.

In fact, as we mentioned in our initial coverage of the Berkeley Earth work, a lot of the papers have a substantial overlap with the existing literature. So much so that it's not clear that Muller and his collaborators will have an easy time getting them published. By extending the instrument record back to 1750, the most recent manuscript does offer something new, but the simple attribution of warming to volcanoes and CO 2 may get hammered during the peer review process.

Muller is a physicist, and that field has a tradition of releasing its papers before peer review (through sites like the preprint host the arXiv). But very few physicists get to announce the arrival of these preprints through editorials in major newspapers. That's partly a result of the fact that even something so well established—the temperatures are going up—has somehow ended up the subject of doubt by over a third of the US population, and the subject of various conspiracy theories.

There also seems to be an element of self-promotion involved. There's an undertone to Muller's op-eds that seems to suggest he feels like it's safe for everyone else to finally believe them, now that he's repeated work that was already accepted by the scientific community. Muller deserves credit for doing much more than most self-described skeptics are willing to do: perform rigorous research designed to address his lingering doubts. But he's being naïve if he seriously thinks that a PR campaign promoting his findings is going to do much to shift the public debate away from basic reality.

The new manuscript can be found here.