I recently showed a couple of breakpoint comparisons for satellite data: RSS versus NOAA and RSS versus UAH. Today, I’ll show a similar comparison for UAH versus NOAA, again stratifying by Land, Ocean and All. (Unfortunately, I was unable to extract a satellite comparison for other major food group: the CRU_TAR (airport tarmac).
Again, the breakpoints are calculated using strucchange and line segments are fitted between breakpoints.
At this point, I’m simply plotting results using a relevant algorithm as an exploratory analysis and am not asserting that any of the breakpoints are “Significant”. Having said that, the breakpoints (which have CIs attached to them) plausibly relate to the (first) termination of NOAA-6 (1983-11), NOAA-10 (1988-10), NOAA-12 (1998-12) and the introduction of AMSU units (2004-12). Here is one more interesting graphic from Christy et al 2000 showing the differences between instrument temperature for different satellites up to 2000 – something that has to be adjusted for. Could errors of 0.2 deg C arise in this standardization? Seems possible to me. Could three errors all be of the same sign? Sure, they could.
The breakpoint structure point to an interesting statistical issue in respect to trend estimation, which may have important implications for the ongoing issue of satellites versus observation. Take a look at the bottom panel (Land). The intra-segment trends are all flat or slightly positive, while the trend without breakpoints is negative – this negative trend is the T2LT warming less than surface (NOAA) warming inconsistent with model expectations.
However, suppose that the breakpoints analysis has identified real breakpoints at important satellite transitions. Is it possible that three inter-satellite adjustments were each off by 0.2 deg C or so (and all in the same direction)? I don’t know enough about the inter-satellite adjustment procedures to comment on this, but my quick perusal of the literature hardly leads me to exclude that possibility.
Let’s also suppose that there were three breakpoints of the sort shown and that otherwise the fluctuations around the trend are white-to-low order red noise. If the breakpoints are not recognized, this will ARIMA-model out as quite high order red noise.
Also if there were breakpoints of the form shown, note that the “true” trend is the composite of the intrasegment trends, which is positive i.e. troposphere warming slightly more than the surface in line with models. So quite a lot turns on breakpoint analysis – an issue that I do not recall being addressed in the CCSP or IPCC reports on this topic. (FWIW, I’ve reflected a bit on this matter, about which much has been made in “skeptical” literature and will try to re-visit it some time. After some reflection, the idea that the tropical troposphere would warm more than the surface doesn’t seem to me to be a particularly unreasonable model property. On the other hand, surface histories of tropical tarmac may have flaws of their own. As also histories of SST with complicated transitions from buckets to engine inlets to buoys.)