1. 1 UIUC ATMOS 397G Biogeochemical Cycles and Global Change Lecture 14: Methane and CO Don Wuebbles Department of Atmospheric Sciences University of Illinois, Urbana, IL March 6, 2003

2. 2 UIUC

3. 3 UIUC Tropospheric OH July -- MOZART II

4. 4 UIUC Tropospheric OH (January) -- MOZART II

5. 5 UIUC OH concentrations OH depends non-linearly on atmospheric concentrations of many tropospheric gases most important gases: CH 4, CO, NO x, tropospheric O 3, NMHCs other factors: tropospheric water vapor, uv radiation flux which depends on stratospheric ozone

6. 6 UIUC Simplified CH 4 /OH/CO Chemistry CH 4 oxidizes to CO OH + CH 4 CO OH + CO OH NMHCs UVO 3 H 2 ONO x

7. 7 UIUC From Daniel Jacob

8. 8 UIUC Decay of an Impulse Emission

9. 9 UIUC Methane: Lifetime vs. Response Time Atmospheric lifetime of CH 4 m  = Burden / flux ~ 9 years — 9.6 years in IPCC (2001) Response time is the e-folding time after a perturbation Response time ~ 1.4 x  ~ 13 years

10. 10 UIUC Trends in Tropospheric OH Based on Krol et al. (2002)

11. 11 UIUC

12. 12 UIUC Estimated Changes in CH 4 Source and Sink From NOAA CMDL, E. Dlugokencky Assumes fixed lifetime of CH4 = 8.9 years Mean emission rate of period of observations is 550 Tg CH 4 yr -1.

13. 13 UIUC Earlier Estimates for Trends in Anthropogenic CH 4 Emissions

14. 14 UIUC Methane Growth Rate

15. 15 UIUC Methane: Changes in Growth Rate 1991-1992 After the eruption of Mt. Pinatubo, a large positive anomaly in growth rate was observed at tropical latitudes. It has been attributed to short-term decreases in solar UV in the tropics immediately following the eruption that decreased OH formation rates in the troposphere (Dlugokencky et al., 1996). A large decrease in growth was observed, particularly in high northern latitudes, in 1992. This feature has been attributed in part to decreased northern wetland emission rates resulting from anomalously low surface temperatures (Hogan and Harriss, 1994) and in part to stratospheric ozone depletion that increased tropospheric OH (Bekki et al., 1994; Fuglestvedt et al., 1994). Records of changes in the 13 C/ 12 C ratios in atmospheric CH 4 during this period suggest the existence of an anomaly in the sources or sinks involving more than one causal factor (Lowe et al., 1997; Mak et al., 2000).

16. 16 UIUC Methane: Changes in Growth Rate 1998 High northern and southern tropical latitudes have been linked to interannual variations in temperature and soil moisture content in wetland regions, thereby affecting CH 4 emissions, and emphasizing the strong link between wetland CH 4 emissions and climate. Observations suggest that global emissions were greater than average by 24 Tg CH 4 A process based model, which included soil-temperature and precipitation anomalies, was used to calculate CH 4 emission anomalies from wetlands of +24.6 Tg CH 4, split nearly equally between high-northern latitudes and the southern tropics [Dlugokencky et al., 2001].

17. 17 UIUC Modeling sources of CH 4 Prediction of methane emissions from scenarios of basic variables including: temperature changes population growth evolution of land use patterns future energy demand and sources technological improvements

18. 18 UIUC 2001 IPCC SRES Projected CH 4 Emissions

19. 19 UIUC Derived Concentrations for Methane

20. 20 UIUC Observed 2-D Model 1992 Pre-ind.

21. 21 UIUC CH 4 only All GHGs Ratio

22. 22 UIUC Reductions in CH 4 Reductions in CH 4, CO and NOx Reduce CO and NOx Reduce CO but not NOx

23. 23 UIUC Change in Total Ozone (%) for 2 x [CH 4 Change in Total Ozone (%) for 2 x [CH 4 ] Δ O 3 = +3.4% University of Illinois 2-D Model Month Latitude

24. 24 UIUC Change in Local Ozone (%) for 2 x [CH 4 Change in Local Ozone (%) for 2 x [CH 4 ] University of Illinois 2-D Model