What information are satellites giving us about temperature changes?
Scientists have studied the air temperature recordings made by satellite instruments since 1979, looking for any trends. The satellite measurements appear to show a slight cooling of the worlds atmosphere about -0.06C per decade. This is despite the global warming trend shown by surface measurements of temperature. However, if short-term events such as El Nio and volcanic eruptions are taken into account, both satellite measurements of the lower atmosphere (the troposphere) and recordings at the surface show slight warming since 1979. In addition, both weather balloons and satellites show that the stratosphere (the layer of the atmosphere from about 12 to 50 kilometres above the ground) is cooling. This is a change that scientists expect to happen as levels of greenhouse gases increase and the ozone layer thins.
Despite the wide range of indicators of global warming, critics often focus on a 23-year period from 1979-2001 when early studies with satellite data showed little or no warming in the lower atmosphere, whereas thermometer data showed that surface temperatures had increased. However, this disparity has declined in recent years. A recent study by Vinnikov and Grody found good agreement between the satellite and surface data from 1978-2002, with a satellite-based warming of 0.24°C per decade compared with 0.17°C per decade from surface data. Another study by Mears et al (2003) found a satellite-based warming of 0.10°C per decade. Santer and others have concluded that apparent inconsistencies between surface and satellite results may be an artefact of satellite data uncertainties. The satellite record is too short to be certain. The longer record of temperature measurements from weather balloons shows that the lower atmosphere has warmed by about 0.10°C per decade from 1958 to 2000, a sim
