There’s a new paper out today, highlighted at RealClimate by Hausfather et al titled Quantifying the Effect of Urbanization on U.S. Historical Climatology Network Temperature Records and published (in press) in JGR Atmospheres.
I recommend everyone go have a look at it and share your thoughts here.
I myself have only skimmed it, as I’m just waking up here in California, and I plan to have a detailed look at it later when I get into the office. But, since the Twittersphere is already demanding my head on a plate, and would soon move on to “I’m ignoring it” if they didn’t have instant gratification, I thought I’d make a few quick observations about how some people are reading something into this paper that isn’t there.
1. The paper is about UHI and homogenization techniques to remove what they perceive as UHI influences using the Menne pairwise method with some enhancements using satellite metadata.
2. They don’t mention station siting in the paper at all, they don’t reference Fall et al, Pielke’s, or Christy’s papers on siting issues. So claims that this paper somehow “destroys” that work are rooted in failure to understand how the UHI and the siting issues are separate.
3. My claims are about station siting biases, which is a different mechanism at a different scale than UHI. They don’t address siting biases at all in Hausfather et al 2013, in fact as we showed in the draft paper Watts et al 2012, homogenization takes the well sited stations and adjusts them to be closer to the poorly sited stations, essentially eliminating good data by mixing it with bad. To visualize homogenization, imagine these bowls of water represent different levels of clarity due to silt, you mix the clear water with the muddy water, and end up with a mix that isn’t pure anymore. That leaves data of questionable purity.
4. In the siting issue, you can have a well sited station (Class1 best sited) in the middle of a UHI bubble and a poorly sited (Class5 worst sited) station in the middle of rural America. We’ve seen both in our surfacestations survey. Simply claiming that homogenization fixes this is an oversimplification not rooted in the physics of heat sink effects.
5. As we pointed out in the Watts et al 2012 draft paper, there are significant differences between good data at well sited stations and the homogenized/adjusted final result.
We are finishing up the work to deal with TOBs criticisms related to our draft and I’m confident that we have an even stronger paper now on siting issues. Note that through time the rural and urban trends have become almost identical – always warming
up the rural stations to match the urban stations. Here’s a figure from Hausfather et al 2013 illustrating this. Note also they have urban stations cooler in the past, something counterintuitive. (Note: John Nielsen-Gammon observes in an email: “Note also they have urban stations cooler in the past, something counterintuitive.”, which is purely a result of choice of reference period.” He’s right. Like I said, these are my preliminary comments from a quick read. My thanks to him for pointing out this artifact -Anthony)
I never quite understand why Menne and Hausfather think that they can get a good estimate of temperature by statistically smearing together all stations, the good, the bad, and the ugly, and creating a statistical mechanism to combine the data. Our approach in Watts et al is to locate the best stations, with the least bias and the fewest interruptions and use those as a metric (not unlike what NCDC did with the Climate Reference Network, designed specifically to sidestep the siting bias with clean state of the art stations). As Ernest Rutherford once said: “If your experiment needs statistics, you ought to have done a better experiment.”
6. They do admit in Hausfather et al 2013 that there is no specific correction for creeping warming due to surface development. That’s a tough nut to crack, because it requires accurate long term metadata, something they don’t have. They make claims at century scales in the paper without supporting metadata at the same scale.
7. My first impression is that this paper doesn’t advance science all that much, but seems more like a “justification” paper in response to criticisms about techniques.
I’ll have more later once I have a chance to study it in detail. Your comments below are welcome too.
I will give my kudos now on transparency though, as they have made the paper publicly available (PDF here), something not everyone does.