An online model of methane in the atmosphere

I’ve put together an easy-to-play-with online model of methane in the atmosphere. I’m going to use it for teaching along with the rest of the Understanding the Forecast webmodels, but it was designed to be relevant to the issue of abrupt new methane burps as we’ve been ruminating about lately on Realclimate.

The model runs in three stages: a pre-anthropogenic steady state which ends in the model year

-50, addition of a new chronic source for 50 years (from human activity),then a spike beginning at model year 0 (supposed to be today) and running for 100 years into the model future. Here are results from the “worst case scenario” in the last post (whether you believe it is the true worst case or not): 200 Gton C over 100 years.

Looks like we got the factor of 10 methane increase about right.

Source and sink of methane in the model.

The lifetime of methane in the atmosphere, used to calculate the methane sink in any time step, is parameterized as a function of concentration following Schmidt and Shindell (2003).

The atmospheric lifetime of methane, used to calculate the sink flux.

The radiative forcing is parameterized from output from the NCAR model, scaled by an efficacy factor of 1.4 from Hansen et al, (2005). The radiative forcing is compared with Business-as-usual CO2 radiative forcing with the model year 0 corresponding roughly to year 2010, and with CO2 rising at 0.65% per year. The methane radiative forcing before year 0 is not time-realistic because the real human sources did not switch on instantaneously 50 years ago, but you can compare the future evolution of radiative forcing from CO2 and methane, from year 0 onwards.

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References

  1. G.A. Schmidt, and D.T. Shindell, "Atmospheric composition, radiative forcing, and climate change as a consequence of a massive methane release from gas hydrates", Paleoceanography, vol. 18, pp. n/a-n/a, 2003. http://dx.doi.org/10.1029/2002PA000757
  2. J. Hansen, "Efficacy of climate forcings", J. Geophys. Res., vol. 110, 2005. http://dx.doi.org/10.1029/2005JD005776