Global Chemistry-Climate Modeling (Lead: ETH Zurich)

The overall objective of WP3 is to provide an understanding of the interactions between natural methane emissions and global climate. Using a global chemistry-climate model, our goals are:

  1. To understand the observed variability of atmospheric CH4 concentrations in the recent past, including an integrated global analysis of the main effects of extreme events like ENSO and volcanic eruptions on methane sources and sink processes
  2. To predict the influence of natural methane emissions on atmospheric CH4 concentrations in the 21st century under a variety of politically likely or extreme scenarios
  3. To determine and analyze feedback processes between the biosphere, atmospheric composition and climate.

Approach and Methods:
We will apply the coupled chemistry-climate model (CCM) SOCOL (Stenke et al., 2012). SOCOL is based on the middle-atmosphere version of the general circulation model ECHAM5 (Roeckner et al., 2003, 2006; Manzini et al., 2006) and the chemistry module MEZON (Egorova et al., 2003). We run the model at T42 horizontal resolution, resulting in a grid spacing of 2.8125° × 2.8125°. In the vertical, a hybrid-sigma coordinate system is used with 39 vertical levels from the surface up to the model top at 0.01 hPa (~80 km). Within MAIOLICA-I the model has been extended towards a comprehensive tropospheric and stratospheric CCM allowing for a consistent simulation of methane emission fluxes and chemistry throughout the whole model domain. In the framework of the proposed project the SOCOL model will be used to perform a series of transient model simulations covering different time periods.

WP3 can be subdivided into 2 activities:
a) Simulations of the recent past from 1990 to 2010 (the period with the best observational coverage for model evaluation),
b) Model forecasts for the future until 2100.

Task 1:
Preparation of model simulations. For activity 3a we intend to apply the model in nudged mode. Our simulations will be set up to guarantee best comparability with the global Lagrangian transport modeling activities in WP2.

Task 2:
Scenario simulations for the recent past (1990-2010). Besides a reference simulation we will perform several sensitivity simulations with respect to different methane emissions inventories as well as the impact of outstanding episodes like strong ENSO events or volcanic eruptions on atmospheric methane. At a later stage of the project, we will perform further sensitivity simulations applying the improved data sets for terrestrial methane emissions from wetlands and biomass burning developed in WP1.

Task 3:
Analysis of key processes driving the observed CH4 variability. The results from our reference run will be extensively validated against satellite and in-situ observations of atmospheric methane. This model validation will be done in close collaboration with WP2. The model simulation will be analyzed with respect to key processes driving the observed CH4 variability by making use of the implemented tracer diagnostic. Combining two model approaches, i.e. a global, low-resolution climate model with interactively coupled chemistry and an Eulerian transport algorithm as well as a global, high-resolution Lagrangian transport model with prescribed OH fields, will provide additional insights into the importance of transport and mixing processes as well as chemical feedbacks for simulated methane concentrations and the relative importance of individual CH4 sources. Particular emphasis will be given to the role of extreme atmospheric conditions like strong ENSO events or volcanic eruptions. The impact of the applied emission data sets will be elucidated by replacing the inventories for individual source categories gradually in a series of sensitivity.

Task 4:
Analysis of CH4 beyond a 2° target. For activity 3b of this work package we will perform long-term ensemble simulations of the 21st century. These model runs serve to investigate the future role of methane in a changing climate, in particular beyond the 2° target. Since the model simulations will be performed with interactively coupled chemistry, we will also take into account future changes in the oxidation capacity of the troposphere including stratospheric feedbacks. For the future simulations we will use different politically likely and extreme scenarios for the evolution of longlived greenhouse gases, methane emissions and land-use changes following the different RCPs (representative concentration pathways) provided within the framework of the IPCC AR5. A comprehensive assessment of future atmospheric methane levels also requires consideration of additional CH4 release from thawing permafrost soils and marine gas hydrates in a warmer climate.
The analysis of the model simulations will focus on the impact of terrestrial (wetland) emissions to future atmospheric CH4 abundances, but also on the relation among interannual CH4 variability and ENSO events. Finally, model results for 2100 will be used to calculate the direct radiative forcing of methane, but also indirect contributions associated with changes in atmospheric composition, in particular ozone and stratospheric water vapor, and to quantify the future contribution of methane to climate change.


  1. Model simulations in nudged mode for the time period 1990-2010
  2. Identification of key processes responsible for the observed variability in atmospheric methane
  3. Model projections of the 21st century under different politically likely and extreme scenarios
  4. A quantitative estimate of the contribution of methane to climate change at the end of the 21st century
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