Interannual Variability of Atmospheric Methane: Possible Effects of the El Niño—Southern Oscillation

Nearly continuous measurements at Cape Meares, Oregon, revealed that methane was increasing in the earth's atmosphere and that its concentration varied cyclically with the seasons. After 6 years of measurements, results show that the rate of increase in methane undergoes interannual variations; the most prominent of these coincided with the last major El Niño-Southern Oscillation, when methane concentrations fell far below expected levels. One of the consequences of the interannual variability is that the long-term rate of increase at Cape Meares is now about 16 parts per billion by volume per year, or about 1 percent annually, which is significantly less than that indicated by the earliest calculations.