Methane Emissions in a Chemistry-Climate Model: feedbacks and climate response

• Main Authors: Heimann, Ines, Griffiths, Paul, Archibald, Alex, Warwick, Nicola, Pyle, John, Abraham, Luke
• Format: Dataset
• Language: English
• Published: Centre for Environmental Data Analysis (CEDA) 2020
• Subjects: Atmospheric sciences and Earth Observation Imagery; Melton; Sea ice
• Online Access: https://dx.doi.org/10.5285/33a2a4b2c2224c5c9a1d17aca747fa19; https://catalogue.ceda.ac.uk/uuid/33a2a4b2c2224c5c9a1d17aca747fa19

This dataset contains methane concentrations from a chemistry-climate model, focusing on year 2000 and year 2100. The present-day forcings were used for the 2000 simulation, while for year 2100 the Representative Concentration Pathway (RCP) RCP8.5 pathway were used. All experiments were run as perpetual timeslice experiments and are global model simulations made using the Met Office Unified Model at vn7.3 based on the HadGEM3-A science configuration. The model was run in atmosphere-only mode with a horizontal resolution of 2.5 degree latitude by 3.75 degree longitude, 60 vertical levels up to 84 km, and prescribed sea surface temperatures and sea ice extents. SST, sea ice and other forcings from earlier model experiments were used, e.g. Banerjee et al. (doi:/10.5194/acp-14-9871-2014). For the year 2000 experiments, greenhouse gas, ozone depleting substances and ozone precursor emissions are taken from the Coupled Model Intercomparison Project - Phase 5 (CMIP5) reference forcings, as in Lamarque, 2010 (doi.org/10.5194/acp-10-7017-2010). The data comprise a series of separate experiments designed to test the performance of methane emissions in this model and to compare against the default that uses a prescribed concentration at the surface, with a view to assessing the performance of the more physically realist emissions treatment. For year 2000, the model was run for three experiments: the first (BASE) experiments employ a set of emissions derived from EDGAR v4 to describe anthropogenic methane emissions, with biognenic emissions taken from the chemistry-transport model (CTM) intercomparison experiment (TransCom-CH4) paper of Patra et al, (DOI:10.5194/acp-11-12813-2011), a second set of experiments used identical emissions to BASE except that CO emissions were increased by 50% globally from the emissions of Lamarque, this is called Delta_CO, and a third year 2000 experiment used CMIP5 methane emissions from Lamarque (as above) rather than EDGAR and biogenic emissions derived from Melton et al. (https://doi.org/10.5194/bg-10-753-2013) rather than Patra. These experiments test the model skill in simulating methane based on the model treatment of emissions and establish the sensitivity to emissions. Three future climate experiments were also performed using climate forcings appropriate to year 2100 following the RCP8.5 pathway. We looked at the climate drivers in turn that arise as the climate changes. In the first, DELTA_CC, climate forcings were adjusted from greenhouse gases to year 2100 values, but kept methane and other anthropogenic forcings at year 2000 values, a second experiment, DELTA_CH4, adjusted CH4 to Year 2100 values from the emissions database as above, a third was an all-forcings experiments in which greenhouse gases, methane and ozone precursors were adjusted to RCP8.5 levels. This gave three separate experiments which explore how methane responds to these changes in the climate drivers.