The concentration of methane has been measured in tropospheric air samples collected in remote locations between 55°N and 53°S during six collection periods between November 1977 and November 1980. The observed concentrations of CH 4 have increased in each of six latitude locations by an average of 0.052±0.005 ppmv between January 1978 and January 1980. This (1.4±0.2)×10 14 gram increase in the total atmospheric burden of CH 4 corresponds to 35±12% of the yearly flux of (4.0±1.3)×10 14 grams needed to maintain the CH 4 concentration in steady‐state at its recent level of about 1.6 ppmv. The 1978‐1980 excess of about 0.7×10 14 grams per year of sources over sinks for CH 4 could arise from either an increase in biogenic releases or from a decrease in the average OH radical concentration in the lower troposphere, or from both.
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