Over the last few days, I’ve shown that Hansen et al 1999 illustrated and discussed the effect of the NASA adjustment for two stations (Phoenix, Tokyo) where the NASA urban adjustment yielded the expected adjustment (denoted in these posts as a “positive” adjustment). In an earlier post, I’d observed that negative urban adjustments (i.e. for nonclimatec urban cooling) had occurred in some Peruvian stations, followed by a post carrying out an inventory of all NASA adjustments – the number of negative adjustments in the ROW proved to be only slightly lower than the number of positive (expected) adjustments.
Unfortunately Hansen et al 1999, the primary reference, did not contain a systematic discussion of any sites with negative adjustments. However, Hansen et al were aware of the existence of negative urban adjustments and it will now be useful to review the original account of the present-day NASA adjustments.
Here’s an important paragraph from Hansen et al 1999:
Examination of this urban adjustment at many locations which can be done readily via our website shows that the adjustment is quite variable from place to place and can be of either sign. In some cases the adjustment is probably more an effect of small-scale natural variability of temperature (or errors) at the rural neighbors rather than a true urban effect. Also the nonclimatic component of the urban temperature change can encompass many factors with irregular time dependence such as station relocations and changes of the thermometer’s environment, which will not be well represented by our linear adjustment. Such false local adjustments will be of both signs and thus the effects may tend to average out in global temperature analyses but it is difficult to have confidence in the use of urban records for estimating climate change. We recommend that the adjusted data be used with great caution, especially for local studies.
Later in the paper, Hansen added the following:
local inhomogeneities are variable; some urban stations show little or no warming, even a slight cooling relative to rural neighbors. Such results can be a real systematic effect e.g. cooling by planted vegetation or the movement of a thermometer away from the urban center or a random effect of unforced regional variability and measurement errors. Another consideration is that even rural locations may contain some anthropogenic influence.
I didn’t notice any other relevant discussions, but will amend this post if any other relevant quotes are brought to my attention.
Let’s review the negative adjustment of 3.3 deg C at Puerto Maldonado in the context of these reviews.
First, I submit that a negative adjustment of 3.3 deg C rises above a “slight cooling relative to rural neighbors”, In an engineering-quality assessment, such results would require specific investigation and explanation.
Second, while “cooling by planted vegetation” can be a feasible mechanism for a type of negative urban heat island in desert settings e.g.here , it seems implausible that this has affected Puerto Maldonado, which is located on an Amazon tributary, or that this is relevant to the vast majority of sites receiving negative urban adjustments.
Third, while we know virtually nothing of the metadata for Puerto Maldonado, it seems unlikely that the cooling relative to “rural” neighbors is due to the “movement of a thermometer away from the urban center”.
Fourth, while I know nothing of the local particulars of Puerto Maldonado climate relative to (say) nearby Cobija, I’d be amazed if there was a 3.3 deg C swing due to “unforced regional variability”. One could certainly not just assume this without some kind of proof.
It seems by far the most likely that the inconsistency between Puerto Maldonado and Cobija is due to something in the staiton histories – some change in instrumentation at Puerto Maldonado or, perhaps in the Bolivian sites, or perhaps both. In the US, where extensive metadata is available, step changes for station moves or instrument changes are included in the various USHCN adjustments (TOBS, MMTS, SHAP, FILNET), none of which are done for the Peruvian and Bolivian stations and is not a “true urban” adjustment.
In Hansens’s terminology, this adjustment would be a “false local adjustment”.
Hansen postulated in very guarded language that these “false” local adjustments would cancel out:
Such false local adjustments will be of both signs and thus the effects may tend to average out in global temperature analyses.
In an engineering-quality study (as opposed to an exploratory scientific article), it would obviously be unacceptable to leave matters in such a state. An engineer would have been obliged to determine whether the effects actually did average out and would not have been permitted to simply leave the matter hanging.
Note that Hansen did not limit the concept of “false local adjustments” to negative adjustments. He clearly contemplated and stated that false local adjustments (i.e. adjustments that did not adjust for urban effect but for local station history issues) would be “of both signs” and, as noted above, that false positive and false negative local adjustments would “average” out.
In my previous post, I calculated the total number of positive and negative NASA adjustments. Based on present information, I see no basis on which anything other than a very small proportion of negative urban adjustments can be assigned to anything other than “false local adjustments”. Perhaps there are a few incidents of vegetative cooling resulting in a true physically-based urban cooling event, but surely this would need to be proved by NASA, if that’s their position. Right now, as a first cut, let’s estimate that 95% of all negative urban adjustments in the ROW are not due to “true urban” effects i.e. about 1052 out of 1108 are due to “false local adjustments”.
On the reasonable assumption that there will be an equal number of positive “false local adjustments” as negative “false local adjustments”, this will yield a total of approximately 2100 “false local adjustments” out of a total population of 2341 adjustments (disregarding bipolar adjustments.) In other words, there is a valid case that about 90% of all NASA adjustments are “false local adjustments”.
If the purpose of NASA adjustments was to do station history homogenizations (a la USHCN), then this wouldn’t matter. But the purpose of the NASA adjustments was to adjust for the “true urban” effect”. On this basis, one can only conclude that the NASA adjustment method is likely to be completely ineffective in achieving its stated goal. As other readers have observed (and anticipated), it appears highly likely that, instead of accomplishing an adjustment for the “true urban effect”, in many, if not most cases, the NASA adjustment does little except coerce the results of one poorly documented station to results from other equally poorly documented stations, with negligible improvement to the quality of whatever “signal” may be in the data.
This does not imply that the NASA adjustment introduces trends into the data – it doesn’t. The criticism is more that any expectation of using this methodology to adjust for urban effect appears to be compromised by the overwhelming noise in station histories. Needless to say, the problems are exacerbated by what appears to be poor craftsmanship on NASA’s part – pervasive use of obsolete station versions, many of which have not been updated since 1989 or 1990(!), and use of population data that is obsolete (perhaps 1980 vintage) and known to be inaccurate.
Some readers have wondered why Hansen even bothered with the entire NASA adjustment project. That seems a very reasonable question. There are a lot of stations where there is no adjustment – wouldn’t it make sense just to use these stations? This takes you into the metadata problem – right now Hansen shows a lot of ROW “rural” stations, but how many of them are actually tropical towns and cities?
I’ll discuss this further tomorrow.