There’s a story at the Telegraph UK from Christopher Booker where he states “…the latest US satellite figures showing temperatures having fallen since 1998, declining in 2007 to a 1983 level…”
Wanting to make sure that there was some data to reference this claim for my readers, I’ve presented some graphs of satellite microwave sounder data below.
MSU data are produced by Remote Sensing Systems and sponsored by the NOAA Climate and Global Change Program. Data are available at www.remss.com
Below are the trend graphs for the data since 1979. Note that these graphs are multi channel, which represent different microwave sounder wavelength channels from the spacecraft. These channels represent different measured levels of the atmosphere.
Channel. TLT – Lower Troposphere
Channel TMT – Middle Troposphere
Channel TTS – Troposphere and Stratosphere combined
Channel TLS – Lower Stratosphere
Above: Global, monthly time series of brightness temperature anomaly for channels TLT, TMT, TTS, and TLS.
All matter emits microwave radiation that varies with its temperature, among other factors. Microwave sensors on weather satellites can take more than 60,000 temperature measurements of oxygen in the atmosphere, from the surface to about 10 km (6 mi) altitude.
NOAA and it’s affiliated researchers have compiled almost three decades of data showing how atmospheric temperature has behaved over the entire globe. At UAH (University of Alabama, Huntsville) where Dr. John Christy and Dr. Roy Spencer have been keeping watch on this trend for some time as well, they have tabular data online should you care to plot it. Here is an ongoing history of the data. You can see some of their other work here.
For Channel TLT (Lower Troposphere) and Channel TMT (Middle Troposphere), the anomaly time series is dominated by ENSO events and slow tropospheric warming. The three primary El Niños during the past 20 years are clearly evident as peaks in the time series occurring during 1982-83, 1987-88, and 1997-98, with the most recent one being the largest. Channel TLS (Lower Stratosphere) is dominated by stratospheric cooling, punctuated by dramatic warming events caused by the eruptions of El Chichón (1982) and Mt Pinatubo (1991). Channel TTS (Troposphere + Stratosphere combined) shows a mixture of both effects.
Temperatures in the lower troposphere (for non weather geeks, that is the portion of the atmosphere where we live) have shown a series of ups and downs since 1979, mostly in a ±0.4oC band, with negligible trends over that period. This contrasts with the near surface temperature record that shows a warming during the same period of time. The graph below is from Wikipedia.
Note in the TLT graph above, the strong 1997-98 El Niño event caused significant lower tropospheric warming in late 1997, and record warmth in February 1998 as evidenced by the spikes shown in the TLT, TMT, and TTS graphs above.
Satellite measurements of the lower stratosphere (TLS) reveal two marked warm periods (as much as 1.5oC warmer), caused by sulfuric acid aerosols deposited in this layer by the eruptions of El Chichón in 1982 and Pinatubo in 1991.
These two warm periods are concurrent with a strong cooling trend over the 19-year period that has been attributed to ozone depletion in the lower stratosphere. In 1997, record low stratospheric temperatures were recorded.
On the TLT graph, for the years 1998 to present, there appears to be a slight downward trend in lower stratospheric temperature, and this is what I believe Christopher Booker is referencing in his article in the Telegraph. Note that there have been other downward trends in the nearly 30 year measurement history, but the overall trend in the TLT, TMT, and TTS channels has been positive, so a short downward trend doesn’t necessarily prove anything. The TLS channel shows a negative trend, and along with the ozone depletion factor, indicates that we aren’t getting much heat transport from the troposphere into the stratosphere.
The real question is whether this small downturn in the tropospheric temperature trend is a short term anomaly, or something indicative of a longer term event. Only time will tell.