National Aeronautics and Space Administration

Publication Supplements

Schmidt and Shindell 2003

The study reported in "Atmospheric composition, radiative forcing, and climate change as a consequence of a massive methane release from gas hydrates" by Schmidt and Shindell (2003) used a simple box model of the troposphere and stratosphere to estimate concentrations of CH₄, stratospheric H₂O, and CO₂ as a function of anomalous emissions of CH₄ into the atmosphere. The documented FORTRAN 90 code that was used for these calculations is available as methane.f. This code consists of two subroutines that can be called from within a carbon cycle model to easily incorporate the atmospheric chemistry and emission changes involving methane.

• init_methane(M): sets the base level of CH₄, calculates the residence time, the proportion of the methane sink that occurs in the troposphere, the stratospheric H₂O due to methane oxidation, and gives an estimate of the multiple of pre-industrial sources required to acheive such a concentration (assuming that no other relevant emissions change).
• methane(em_anomaly,CH4,H2O_strat,dCO2_anomaly,dt): using the emission anomaly (Gt/carbon per yr), this subroutine updates the CH₄ and stratospheric H₂O levels, and returns the amount of CO₂ (in Gt/carbon) that arises from methane oxidation.
• sink(CH4): this function estimates the relative specific loss rate for methane in the troposphere as a function of the methane concentration using a look-up table that summarises results from the 2D tropospheric-stratospheric chemistry model described in the paper.

Please address any comments or questions about this FORTRAN code to Dr. Gavin Schmidt.