Global-Average Surface Temperature

Measurements of the global-averaged surface temperature of the Planet Earth show that this temperature has increased by about 0.5^oC over the last 100 years. This increase with time has not been uniform. Figure 3 shows there was a reasonably steady rise from 1860 to a peak in the 1940's and then a drop off to the 1970's followed by a very dramatic rise since about 1970. Recent data show that 1998 has been the hottest year in the 138-year historical record and that six of the eight warmest years have occurred since 1998. The extraordinary warmth in 1998 was largely due to a very strong El Niño. The demise of this El Niño allowed global temperatures to drop back somewhat, but then resume an increase to the point where at the end of 2005, global mean temperatures equaled those of the 1998 El Niño year even though we had no El Niño in progress at this time.

There is now good evidence that at least part of this rise in temperature is caused by the increases in carbon dioxide, methane and other trace gases that are produced as a result of anthropogenic (human) activities. There is good physical evidence to support this because we know carbon dioxide and methane absorb infrared radiation and are contributing to this recent rise in temperature.

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