As a simple exercise, I quickly revisited the everchanging Hansen adjustments, a topic commented on acidly by E.M. Smith (Chiefio) in many posts – also see his interesting comments in the thread at a guest post at Anthony‘s, a post which revisited the race between 1934 and 1998 – an issue first raised at Climate Audit in 2007 in connection with Hansen’s Y2K error.
As CA readers recall, Hansen’s Y2K error resulted in a reduction of US temperatures after 2000 relative to earlier values. The change from previous values is shown in red in the graphic below; the figure also shows (black) remarkable re-writing of past history since August 2007 – a rewriting of history that has increased the 2000-6 relative to the 1930s by about 0.3 deg C.
This impacts comparisons made in 2007 between GISS and CRN1-2 stations. At the time, it was noted that GISS adjustments for UHI resulted in the GISS US temperature anomaly having quite a bit in common with a TOBS average from Anthony’s CRN1-2 stations.
Critics of Anthony’s surfacestations.org project commented on this rather smugly – too smugly given the large differences with NOAA and CRU versions in the US and the incoherence of Hansen’s adjustments outside the US. The post-2007 adjustments to GISS adjustments change this.
The increased trend in the GISS US statistic comes at the expense of reconciliation with CRN1-2 stations: the trends no longer cohere.
In the past, Hansen said that he was too busy to joust with jesters – see here. At the time, I observed:
presumably he’s too busy adjusting to have time for jousting. We by contrast have lots of time to jest with adjusters.
Little did we appreciate that Hansen’s new adjustments were not in jest.
Update Dec 26– Hansen’s new article on GISTEMP – Hansen et al 2010 here updates Hansen et al 1999, 2001. Section 4 contains a discussion of US adjustments under different systems, each purporting to show that UHI doesn’t matter. Later in section 9, there is a section on US adjustments, with a brief whining mention of the Y2K adjustment and the following graphic purporting to show that change to USHCN v2 had negligible impact.
It is entirely possible that the change in GISS US since August 2007 is primarily due to the replacement of USHCN v1 methodology (TOBS and that sort of thing that we discussed in the past) with Menne’s changepoint methodology used in USHCN v2.
Menne’s methodology is another homemade statistical method developed by climate scientists introduced without peer review in the statistical literature. As a result, its properties are poorly known.
As I mentioned some time ago, my impression is that it smears stations together so that, if there are bad stations in the network, they influence good stations. Jones used the Menne method in Jones et al 2008, his most recent attempt to show that UHI doesn’t “matter.”
My guess is that it will be very hard to construct circumstances under which UHI will matter after data has been Menne-transformed. And that tests of the various night lights scenario on data after it has been Menne-transformed will not tell you very much. This is just a surmise as I haven’t waded through Menne code. (I requested it a number of years ago, but was unsuccessful until 2009.)
It’s too bad that the Menne adjustment methodology wasn’t published in statistical literature where its properties might have been analysed by now. It’s a worthwhile topic still.