Water vapor is the most important greenhouse gas, followed by carbon dioxide and other trace gases. However, the concern is not with the fact that we have a greenhouse effect, but it is with the question regarding whether human activities are leading to an enhancement of the greenhouse effect. There is no scientific debate on this point. The warming has not been globally uniform. The recent warmth has been greatest over N. America and Eurasia between 40 and 70 N. Warming, assisted by the record El Ni o of 1997-1998, has continued right up to the present.
Linear trends can vary greatly depending on the period over which they are computed.
Furthermore, there are small unresolved differences between radiosonde and satellite observations of tropospheric temperatures, though both data sources show slight warming trends. If one calculates trends beginning with the commencement of radiosonde data in the 1950s, there is a slight greater warming in the record due to increases in the 1970s. Cloud cover has increased in many of the areas with reduced diurnal temperature range. Relatively cool surface and tropospheric temperatures, and a relatively warmer lower stratosphere, were observed in 1992 and 1993, following the 1991 eruption of Mt. Pinatubo. The warming reappeared in 1994.