Measurements of an anomalous global methane increase during 1998

Abstract

Measurements of atmospheric methane from a globality distributed network of air sampling sites indicate that the globality averaged Ch 4 growth rate increased from an average of 3.9 ppb yr -1 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 CH 4 sources and sinks equal to -24 Tg CH 4 the largest perturbation observed in 16 years of measurements. We suggest that wetland and boreal biomas 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 CH 4 from wetlands north of 30°N and 13 Tg CH 4 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 × 10 5 km6 2 of forest and pest land burned releasing an estimated 5.7 Tg CH 4.