Guest post by John Goetz
As noted in the previous post, GISS has released their monthly global temperature summary for June, 2009. This month’s whopping anomaly of 0.63C is once again much higher than that of RSS, UAH, and even NOAA, which is the source of the GISS temperature data. Not only is the anomaly higher than the other metrics, but it is trending in the opposite direction.
Temperature data from 1079 stations worldwide contributed to the analysis, 134 of them being located in the 50 US states. Data from essentially the same few stations have been used for the past twenty-four months. Many, many hundreds of stations that have historically been included in the record and still collect data today continue to be ignored by GISS in global temperature calculations.
Once again, the bulk of temperatures comprising the present-day worldwide GISS average come from airports – in this case 554 airports, according to the NOAA metadata from the V2 station inventory. In the US, the ratio of airports to total stations continues to run very high, with 121 out of the 134 reporting stations being located at airports.
Why worry about airports? Aside from recent posts on this site documenting problems with airport ASOS equipment in the US, WUWT has also documented a number of equipment siting problems, notably the typical close proximity of the equipment to a tarmac heat sink. Airports can introduce a mini-UHI effect where one would otherwise not be found.
The NOAA metadata is not entirely accurate, and several stations located at airports are not noted as such. Some examples include Londrina and Brasilia in Brazil, Ely / Yelland in Nevada, and Broome in Austrailia. Those stations were easy to find because they had “airport” (or some variant) in the station name. A check of coordinates using Google Earth confirmed the airport locations.
Let’s examine the metadata a little further, shall we?
NOAA says that 345 of the stations it passes on to GISS are rural and presumably free of UHI influence. Fifteen of those stations are located in the US. However, only 201 of those rural stations are not located at an airport, and therefore presumably free of UHI effects (including tarmac heat sinks). In the US, only one of the fifteen stations is listed as both rural, and not located at an airport: Ely / Yelland in Nevada.
Doh!!! As noted above, that station is located at an airport – confirmed not just by Google Earth, but also by NOAA’s NCDC website as well! This means that all of the US temperatures – including those for Alaska and Hawaii – were collected from either an airport (the bulk of the data) or an urban location.
As for the rest of the world, some of the stations listed as being rural and not at an airport have metadata indicating they are located in an area of “dim” or “bright” lights. Filtering those out, we find a total of 128 stations that are rural, not at an airport, and “dark”.
Why are “dark” stations important? Recall that GISS uses dark stations to adjust for UHI in the urban stations. With only 128 dark stations available, none being in the US, it would seem this is an impossible task.
Fortunately, GISS adjustment rules allow old data to be used in adjusting new data. The older “non-reporting” rural weather stations continue to adjust reporting urban stations, even though the most recent two years of overlap is missing.
Thankfully, the algorithms are robust enough to calculate adjustments to the 100th of a degree even when data is missing.