Ref: Frank J. Wentz and Matthias Schabel, "On the discrepancy between observed in situ warming and the cooling trend in MSU tropospheric temperatures"

This research paper, submitted to Nature on Feb. 23rd and widely leaked, attacks the results of the MSU (Microwave Sounding Unit) instrument flown on NOAA weather satellites since 1979. According to their analysis, the reported negative temperature trend (of about minus 0.05°C per decade) by Channel 2R may turn into a positive trend of 0.07°C per decade -- still well below the value of 0.2 to 0.3°C calculated by climate models and endorsed by the IPCC.

Wentz shows that the small decrease in satellite altitude due to atmospheric drag, about 15 km from a mean altitude of 850 km, may be sufficient to affect the Spencer/Christy analysis leading to the 2R result of tropospheric cooling since 1979. This comes about because 2R is synthesized by subtracting data from different view angles of Channel 2 (which covers the whole troposphere) in order to concentrate the response to the lower-most region of the troposphere.

Frank Wentz is a well-respected remote-sensing expert of considerable ability, and the glitch that he found in the satellite data analysis appears to be genuine. His research paper adds to a better understanding of the satellite data and certainly deserves to be published. The effect he discovered, however, may be offset and canceled by other effects that are now being investigated.

Dr. Roy Spencer, at the NASA Marshall Center in Huntsville AL, told us the following:

1. Wentz's criticism of Channel 2R is basically correct. But he has applied his effect to adjusted data, which gives it a stronger impact. This is wrong; it should really be applied only to the raw data.

2. The effect Wentz found--orbital decay creating a false cooling trend in the satellite temperature data--may be offset by two compensating effects that Spencer is now checking out: orbital precession of the satellites and calibration drift in the radiometer, which would create a false warming trend.

3. Support for an offsetting effect can be found in the strong correlation between the weather satellite temperature data and the (independent) balloon radiosonde temperature data. The effect Wentz is talking about would not apply to balloon radiosondes, so if it were really distorting the satellite data, those two records should diverge. They do not.

Two Comments:

1. Wentz used sea surface temperatures as a substitute for tropospheric temperatures. But SST and atmospheric temperatures can be very different. Also, the various ways that sea surface temperatures are combined--buckets, ship intake water, buoys, land stations on islands, etc., all thrown into the hopper--make the end result for SST dependent on the mix. A change in the mix of data sources over time could cause an artificial temperature trend.

2. The satellite data showing a cooling trend have been under attack by scientists who believe in the correctness of climate models that calculate a strong warming trend. In a 1997 paper in Nature, James Hurrell and Kevin Trenberth had also criticized the MSU results, claiming that a negative bias was introduced when records of different satellites were joined; Spencer/Christy do not accept this criticism. Question: Does the Wentz effect make the Hurrell/Trenberth criticism moot?

The bottom line: Wentz has an interesting research paper, and it certainly adds to our understanding of this part of the global warming discussion, but the net effect at this point looks like no change.

P.S. The way the Wentz paper is being handled raises eyebrows: i.e., circulated to core global warming promoters; rushed into print in a publication that has been increasingly ideological on the global warming issue; refusing to hold up until a response can be submitted alongside; brought to the attention of IPCC chairman Robert Watson and Vice President Albert Gore (who was reportedly "ecstatic"); and without a doubt leaked to the press at a time when the EPA is trying to circumvent Senate ratification of the Kyoto Accord.

This issue has been aired by Congressman John Peterson in a letter over the Internet. It's on the SEPP web page, the Junk Science page, the John Daly "Still Waiting for the Greenhouse" page, and has turned up on CNN's global warming on-line debate. (By e-mail, Peterson's letter may have already circled the globe three times).