Temperatures measured from satellites

Satellites provide another source of global temperature trend information by measuring microwave light emission from oxygen gas, O2, in the atmosphere. Because of the way that electrons are distributed around the nuclei of oxygen molecules, the rotation of oxygen molecules emits and absorbs energy in the microwave range of light. This is longer wavelength, lower energy light than the IR light that greenhouse gases absorb and emit. Microwave light does not carry much energy in the Earth's energy budget, so we have not been considering O2 as a greenhouse gas the way we do CO2. The difference is that microwave emission comes from rotation rather than vibration, and the frequency of light this generates falls outside the main blackbody spectrum of the Earth (Chapter 4).

The intensity of microwave radiation emitted from O2 increases with increasing temperature, just as the intensity of IR light goes up with temperature. The satellites measure microwave emission in a range of wavelengths, and from these measurements construct temperature estimates for several regions of the atmosphere (see http://mtp.jpl.nasa.gov/intro/intro.html). The lowermost region of the atmosphere from which the satellite estimates the temperature spans from the surface to about 8 km altitude, with an exponential decay, rather similar in shape to the curve describing pressure with altitude (Fig. 5.2).

These satellite temperature estimates have been the subject of considerable scientific and political discussion because for many years the satellite estimates of warming disagreed with the reconstructions from thermometers. This has now changed, as scientists learn how to calculate temperature from the raw satellite sensor data (solid black line in Fig. 11.3). The satellite temperature record comes from a series of satellites which must be well calibrated against each other as they are pieced together into a longer composite record. The raw data must be corrected for things like changes in the orbit of the satellite. The current calibration of the satellite data shows good agreement with the land and sea instrumental records.

1880 1900 1920 1940 1960 1980 2000 Year

Fig. 11.3 A comparison of the global average temperature reconstruction with the satellite record. Data replotted from Mears and Wentz (2005).


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Instrumental record

Fig. 11.3 A comparison of the global average temperature reconstruction with the satellite record. Data replotted from Mears and Wentz (2005).

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Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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