CLIMATOLOGY

Water Flowing Upward

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Science  20 Apr 2001:
Vol. 292, Issue 5516, pp. 399
DOI: 10.1126/science.292.5516.399b

Water vapor is an important component of the radiative behavior and the chemistry of the stratosphere, especially in the ozone cycle. It is supplied mostly by mixing with the underlying troposphere and by the oxidation of methane, and both processes are thought to be influenced directly or indirectly by anthropogenic activity. The longest continuous data set of stratospheric water vapor abundance extends back only to 1980, so longer trends can be determined only by combining it with other records. Rosenlof et al. have compiled and analyzed ten data sets, which cover the period from 1954 to 2000, and show that the mixing ratio of stratospheric water vapor has increased steadily but irregularly by 2 parts per million by volume during that time (an average rate of about 1% per year). They calculate that this rise is greater than that which can be explained by increases in tropospheric methane concentrations, which implicates changes in the transport of water vapor into the tropical stratosphere as a probable cause. — HJS

Geophys. Res. Lett.28, 1195 (2001).

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