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Dlugokencky, E.J., B.P. Walter, K.A. Masarie, P.M. Lang, and E.S. Kasischke, 2001: Measurements of an anomalous global methane increase during 1998. Geophys. Res. Lett., 28, 499-502, doi:10.1029/2000GL012119.
Measurements of atmospheric methane from a globally distributed network of air sampling sites indicate that the globally averaged CH4 growth rate increased from an average of 3.9 ppb /yr during 1995-1997 to 12.7±0.6 ppb in 1998. The global growth rate then decreased to 2.6±0.6 ppb during 1999, indicating that the large increase in 1998 was not a return to the larger growth rates observed during the late-1970s and early-1980s. The increased growth rate during 1998 corresponds to an increase in the imbalance between CH4 sources and sinks equal to ~24 Tg CH4, the largest perturbation observed in 16 years of measurements. We suggest that wetland and boreal biomass burning sources may have contributed to the anomaly. An adaptation of a global process-based model, which included soil-temperature and precipitation anomalies, was used to calculate emission anomalies of 11.6 Tg CH4 from wetlands north of 30°N and 13 Tg CH4 for tropical wetlands during 1998 compared to average emissions calculated for 1982-1993. For 1999, calculated wetland emission anomalies were negative for high northern latitudes and the tropics, contributing to the low growth rate observed in 1999. Also 1998 was a severe fire year in boreal regions where ~1.3×105 km2 of forest and peat land burned releasing an estimated 5.7 Tg CH4.
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