# Presentation: 207441

## Biogenic Contributions to Methane Trends from 1990 to 2004

**Biogenic Contributions to Methane Trends from 1990 to 2004**

**Arlene M. Fiore****1 ****(arlene.fiore@noaa.gov), Larry W. Horowitz****1****, Ed Dlugokencky****2****, J. Jason West****3**
** ****1****NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ  ****2****NOAA Global Monitoring Division, Earth System Research Laboratory, Boulder, CO  ****3****Atmospheric and Oceanic Sciences Program and Woodrow Wilson School, Princeton University, Princeton, NJ**

** ****1. Introduction**

**REFERENCES****	**
- Dentener, F., *et al*. (2003), *J. Geophys. Res., 108*, 4442, doi:10.1029/2002JD002916.
- Dlugokencky, E.J., *et al*. (2003), *Geophys. Res. Lett., 30*, 1992, doi:10.1029/2003GL018126.
- Dlugokencky, E.J., *et al*. (2005), *J. Geophys. Res., 110*, D18306, doi:10.1029/2005JD006035.
- Horowitz, L.W., *et al*. (2003), *J. Geophys. Res., 108*, 4784, doi:10.1029/2002JD002853.

**What is the contribution from each process?**
**Are existing bottom-up CH****4**** emission inventories **
**for the 1990s consistent with observations?**** **

**2. Methane in the MOZART-2 CTM**

**3. Influence of Sources on Surface CH****4**** Distribution and Trend**

**4. Meteorologically-driven Changes in the CH****4**** Lifetime**

**Methane (CH****4****) emission controls are a cost-effective strategy for abating global surface ozone, while simultaneously slowing greenhouse warming [*****West and Fiore*****, 2005].  Sources of CH****4**** are shown to the right; the major CH****4**** sink is reaction with the hydroxyl radical (OH) in the troposphere. Surface CH****4**** concentrations rose by 5-6 ppb yr****-1**** on average until 1999 when they leveled off (see Figure below). There is no clear consensus on the driving mechanism. **

**Possible explanations suggested by previous studies:**
** ****Source changes of CH****4**** [*****e.g*****. *****Langenfelds et al*****., 2002; *****Wang et al*****.,  2004] or other species [*****e.g*****. *****Karlsd******ó******ttir and Isaksen*****, 2000]**
** ****Meteorologically-driven changes in the CH****4**** sink [*****e.g.***** *****Warwick et  al*****., 2002; *****Dentener et al*****., 2003; *****Wang et al*****., 2004]**
** ****Approach to steady-state with constant lifetime **
**    ****[*****Dlugokencky et al*****., 2003]**

**BASE**
**Constant emissions (1990)**

**Sensitivity simulations applying different CH****4**** emission inventories:**

**Latitudinal **
**distribution **
**of 1990 CH****4**** **
**emissions **
**for each case**

**ANTH**** **
**Time-varying anthrop. emissions**

**ANTH + BIO **
**Time-varying anthrop. and **
**wetland emissions**

- Tg CH4 yr-1

-  EDGAR v3.2 1990 and 1995 anth.
-    emissions [*Olivier*, 2002]
-  EDGAR “FAST-TRACK” for 2000
-    [*van Aardenne et al*., 2005]
-  Linear interpolation applied for
-    intermediate years
-  Biogenic source adjusted to
-    maintain same global total
-    emissions in 1990 as in BASE

- Combine wetland emissions from
*Wang et al*. [2004] (above) and
- anthropogenic emissions from
- ANTH, constraining global mean
- 1990-1998 wetland emissions
- to equal those in ANTH

****** ****Recycled NCEP 1990-2004 **

****** ****Meteorological drivers for observed trend **
** ****Not just simple approach to steady-state**

**Area-weighted global mean surface CH****4**
**in BASE simulation (constant emissions)**

**BASE**** ****captures observed rate of increase**** ****1990-97**
**and leveling off **
**after 1998**

- Global mean surface CH4 concentrations as measured (or sampled in the model) at 42 Global Monitoring Division (GMD) stations [*e.g.* *Dlugokencky et al*., 2005] with an 8-year minimum record. Values are area-weighted after averaging in latitudinal bands (60-90N, 30-60N, 0-30N, 0-30S, 30-90S).

**How might meteorology affect**** ********? **

**OBS (GMD)     ****BASE     ****ANTH     ****ANTH+BIO**

****** ****Model captures the observed seasonal cycles **

**CH****4 ****Lifetime Against **
**Tropospheric OH (********) **

** ****Mean annual CH****4**** lifetime shortens**

- Surface CH4 concentrations at selected GMD stations

**BASE simulation (constant emissions) captures observed rate of CH****4**** increase from 1990-1997, and leveling off post-1998**
**ANTH emissions (EDGAR 3.2 + FT-2000 inventories) improve modeled CH****4**** post-1998**
**ANTH+BIO spatial and temporal distribution of wetland CH****4**** emissions is critical for reproducing the observed seasonality, interhemispheric gradient, and global mean trend**
** ********CH4**** decreases by ~2% from 91-95 to 00-04 due to warmer temperatures (35%) and higher OH (65%, resulting from a ~10% increase in lightning NO****x ****emissions)**
**Future research should:**
** ****consider climate-driven feedbacks from biogenic emissions and fires (CH****4****, CO, NO****x****, NMVOC) on ********CH4**
** ****develop more physically-based parameterizations of lightning NO****x**** emissions to determine whether  **
**    ****higher emissions are a robust feature of a warmer climate**

**10.40**

**10.23**

- van Aardenne, J.A., F. Dentener, J.G.J. Olivier and J.A.H.W. Peters (2005), The EDGAR 3.2 Fast Track 2000 dataset (32FT2000).
- Wang , J.S., et al. (2004), Global Biogeochem. Cycles, 18, GB3011, doi:10.1029/2003GB002180.
- Warwick, N.J., *et al*. (2002), *Geophys. Res. Lett., 29* (20), 1947, doi:10.1029/2002GL015282
- West, J.J. and A.M. Fiore (2005), *Environ. **Sci. & Technol., 39, *4685-4691.

****** ****OH increases in the model by +1.4% from 1991-1995 to 2000-2004   **
**     ****due to a 0.3 Tg N yr****-1**** (~10%) increase in lightning NO****x **
****** ****Large uncertainties in magnitude (and trend) of lightning NO****x**** **
**     ****emissions in the real atmosphere**

- Karlsdóttir, S., and I.S.A. Isaksen (2000), *Geophys. Res. Lett., 27* (1), 93-96.
- Langenfelds, R.L., et al. (2002), *Global Biogeochem. Cycles, 16*, 1048, doi:10.1029/2001GB001466.
- Olivier, J.G.J., *et al*. (1999), *Environmental Science & Policy, 2*, 241-264.
- Olivier, J.G.J. (2002) In: "CO2 emissions from fuel combustion 1971-2000", 2002 Edition, pp. III.1-III.31. International Energy Agency (IEA), Paris. ISBN 92-64-09794-5.

**nmol/mol = ppb in dry air**

**nmol/mol = ppb in dry air**

**5. Conclusions**

** ****~100 gas and aerosol species, ~200 reactions**
** ****NCEP meteorology 1990-2004**
** ****1.9****o**** latitude x 1.9****o ****longitude x 64 vertical levels**
** ****detailed description in *****Horowitz et al*****. [2003]**

**Deconstruct ************ (-0.17 years) from 1991-1995 **
**to 2000-2004 into individual contributions by **
**varying temperature and OH separately**