Globally-averaged methane mixing ratios are collected approximately weekly from various sites in the NOAA/CMDL cooperative air sampling network (Dlugokencky et al. 1994). Air sampling sites are distributed between 90oS and 82oN. The average increase in the globally- averaged methane mixing ratio over the period 1983-1993 is approximately 0.6% per year when referenced to the middle of the sampling record (Fig. 1.19). The growth of methane over the past few years has slowed, probably due to a change in the anthropogenic source (Dlugokencky et al. 1994). Increased methane affects the Earth's radiation balance and the chemistry of the atmosphere. While the major sources of methane have been identified, their absolute contributions to the global methane budget remain poorly quantified. Until a better understanding of the methane budget is realized, the exact causes of the observed increase will remain uncertain. It is clear, however, that the increase in atmospheric methane is related to increased methane emissions from sources directly influenced by human activity.
Climate and Global Change Issues - Cryosphere: Snow Cover
Climate and Global Change Issues - Trace Gases: Carbon Dioxide
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