# Presentation: 207439

## Source vs. Sink Contributions to Atmospheric Methane Trends: 1990-2004

**Source vs. Sink Contributions to Atmospheric Methane Trends: 1990-2004**

**Arlene M. Fiore **
**Larry Horowitz (NOAA/GFDL)**
**Ed Dlugokencky (NOAA/GMD)**** **
**Jason West (Princeton)**
**Informal Seminar at NOAA GMD**
**January 24, 2006**

## More than half of global methane emissions 

**More than half of global methane emissions **
**are influenced by human activities**
- ~300 Tg CH4 yr-1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; *Olivier et al*., 2005]
- ~200 Tg CH4 yr-1 Biogenic sources [*Wang et al*., 2004]

**ANIMALS**
**90**

**LANDFILLS +**
**WASTEWATER**
**50**

**GAS + OIL**
**60**

**COAL**
**30**

**RICE 40**

**TERMITES**
**20**

**WETLANDS**
**180**

**BIOMASS BURNING + BIOFUEL    **
**            ****30**

**GLOBAL METHANE**
**SOURCES **
**(Tg CH****4**** yr****-1****) **

## Observed trend in Surface CH4 (ppb) 1990-2004

- Data from 42 GMD stations with 8-yr minimum record is area-weighted, after averaging in bands
- 60-90N, 30-60N, 0-30N, 0-30S, 30-90S

**GMD Network**

**Global Mean CH****4**** (ppb)**

**Hypotheses for leveling off**
**discussed in the literature:**
**1. Approach to steady-state**
** **
**2. Source Changes   **
**       ****Anthropogenic**
**Wetlands**
**Biomass burning**
**3. Transport**
**4. Sink (OH)**
**         ****Humidity**
**         ****Temperature**
**         ****OH precursor emissions**
**         ****overhead O****3**** columns**

**How does a 3-D forward model compare with GMD observations?**

## 	Model with constant emissions largely captures observed trend in CH4 during the 1990s  

**	****Model with constant emissions largely captures ****observed trend in CH****4**** during the 1990s  **

**MOZART-2  [*****Horowitz et al*****., 2003]**

**NCEP**
**1.9°x1.9°**
**28 ********-levels**
**EDGAR v.2.0 **
**    ****emissions**
**CH****4**** EDGAR **
**    ****emissions **
**    ****for 1990s**

## Bias and Correlation vs. GMD Surface CH4: 1990-2004

**Bias and Correlation vs. GMD Surface CH****4****: 1990-2004**

**BASE ****simulation with constant emissions:**
** ****Overestimates interhemispheric gradient **
** ****Correlates poorly at high northern latitudes**

**BASE**

**Mean Bias (ppb)**

**r****2**

## Estimates for Changing Methane Sources in the 1990s

**547**

**Tg CH****4**** yr****-1**

**EDGAR anthropogenic inventory**

- Biogenic adjusted to maintain
- constant total source

**BASE**

## Bias & Correlation vs. GMD CH4 observations: 1990-2004

**OBS**
**BASE**
**ANTH**

**Mean Bias (ppb)**

**r****2**

**Bias & Correlation vs. GMD CH****4**** observations: 1990-2004**

**ANTH**** ****simulation with**** time-varying EDGAR 3.2 emissions****:**
****** ****Improves abundance post-1998**
** ****Interhemispheric gradient too high **
** ****Poor correlation at high N latitudes**

## Bias & Correlation vs. GMD CH4 observations: 1990-2004

**Mean Bias (ppb)**

**ANTH+BIO**** ****simulation with**** time-varying EDGAR 3.2 ****+ wetland emissions ****improves:**
****** ****Global mean surface conc.**
****** ****Interhemispheric gradient **
** ****Correlation at high N latitudes**

**Bias & Correlation vs. GMD CH****4**** observations: 1990-2004**

**OBS**
**BASE**
**ANTH**
**ANTH+BIO**

**r****2**

**S****	****     Latitude****	****            N**

## Methane Concentration (nmol/mol = ppb)

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

**Model **
**captures**
**distinct **
**seasonal**
**cycles at **
**GMD **
**stations**

## Time-Varying Emissions:  Summary

**Next: Focus on Sinks**
**-- Examine with BASE model (constant emissions)**
**-- Recycle NCEP winds from 2004 “steady-state”**

**OBS**
**BASE**
**ANTH**
**ANTH+BIO**

** ****Annual mean CH****4**** in the   **
** “****time-varying ANTH+BIO” **
**  ****simulation best captures  **
**  ****observed distribution **

## Methane rises again when 1990-1997 winds are applied to “steady-state” 2004 concentrations

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

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

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

## How does meteorology affect the CH4 lifetime? 

**r****2**** = 0.83**

**How does meteorology affect the CH****4 ****lifetime? **

**10****5**** molecules cm****-3**

**Lifetime Correlates Strongly With Lower Tropospheric**
**           ****	****            ****OH                  and              Temperature**

**r****2**** = 0.51**

**r****2**** = 0.89 vs. OH**
**if 1998 neglected**
**(0.80 for Temp)**

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

******T(+0.3K)**

******OH(+1.4%)**

**BASE**

- +

- =

** ****OH increases in the model by 1.4% due to a 0.3 Tg N yr-1 **
**     ****increase in lightning NO****x**** emissions  **
**Large uncertainties in magnitude (and trend) of lightning NO****x**
**     ****emissions in the real atmosphere**

## Methane Distribution and Trends:  Conclusions

**Methane Distribution and Trends:  Conclusions**

**Global Mean CH****4**** (ppb)**

**OBSERVED**

******CH4**** decreases by ~2% from 1991-1995 to 2000-2004 due to warmer temperatures (35%) and higher OH (65%), resulting from a 10% increase in lightning NO****x ****emissions**

**BASE (constant emissions) captures observed rate of increase 1990-1997 and leveling off post-1998**
**ANTH improves modeled CH4 post-1998**
**Wetland emissions in ANTH+BIO best match observed seasonality, inter-hemispheric gradient and global trend**

## Q: How will future global change influence atmospheric CH4?Potential for complex biosphere-atmosphere interactions...can be studied with GFDL earth system model

**CH****4**** + ****OH****      ...****products**** **

**Soil **

**BVOC**

**NO****x**