HR: 1330h
AN: A52B-0794    [PDF]
TI: Is the Global Atmospheric Methane Budget at Steady-State?
AU: * Dlugokencky, E J
EM: ed.dlugokencky@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Houweling, S
EM: s.houweling@phys.uu.nl
AF: National Institute for Space Research, Princetonplein 5, Utrecht, 3584 CC Netherlands
AU: Bruhwiler, L
EM: lori.bruhwiler@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Masarie, K A
EM: kenneth.masarie@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Lang, P M
EM: patricia.m.lang@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Miller, J B
EM: john.b.miller@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, CO 80305 United States
AU: Tans, P P
EM: pieter.tans@noaa.gov
AF: NOAA Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Boulder, CO 80305 United States
AB: The atmospheric CH$_{4}$ abundance began increasing near the start of the industrial revolution, and this increase continued through the 20th century. But during the past 4 years (1999 to 2002), the global abundance of atmospheric CH$_{4}$, as determined from an extensive network of air sampling sites, has been approximately constant at 1751 ppb. If it is assumed that the CH$_{4}$ lifetime has been constant over this 4-year period, then the global CH$_{4}$ budget has been at steady state. Although the growth rate of CH$_{4}$ decreased from about 15 ppb yr$^{-1}$ in the early 1980s to a few ppb yr$^{-1}$ in the late 1990s, it seems unlikely that the global CH$_{4}$ budget could have already reached steady-state without a reduction in emissions. Our measurements support such a reduction; we have observed a significant decrease in the difference between polar northern and polar southern zonal averages of CH$_{4}$ from 1991 to 1992. Using a 3-D transport model, we show that this change is consistent with a decrease in CH$_{4}$ emissions of $\sim$10 Tg from north of 50$\deg$N in the early-1990s, which may have accelerated the global CH$_{4}$ budget towards steady state. Based on current knowledge of the global CH$_{4}$ budget and how it has changed with time, it is not possible to tell if the atmospheric CH$_{4}$ burden has peaked, or if we are only observing a persistent, but temporary pause in its increase.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting