Continuing our series.....

on the emission scenerios in Hansen, et al, 1988 (implicit to Hansen's congressional testimony) we now show a comparison between the predicted methane concentrations from Scenerios A, B and C.

(Click on image to enlarge and make clearer)

There is a bit of a cheat here. Hansen, et al. assumed that the mixing ratio was 1.4 ppb in 1958. The figure above assumes 1.34 to give the best fit to the data. The figure below shows the mixing ratios assuming 1.40, 1.34 and 1.30 ppb in 1958 with Scenerio C as described in Hansen et al.

(Click on image to enlarge and make clearer)

There are a number of issues here. First of all the methane mixing ratio series does not extend as far back as that for CO2. Eli is using Blake's (UC Irvine) data which extends back to 1979. Blake analyzes grab samples by gas chromatography with a flame ionization detector. This is an accurate and sensitive method. Samples are taken at fixed sites at different latitudes (Mauna Loa and Antarctic stations are used) and on ship transects. Keep in mind that since methane has an atmospheric lifetime of only a few years, that concentration will vary with latitude and altitude, since the sources are at the surface and emissions are concentrated in the northern hemisphere. Thus it is not trivial to say which of the three starting points is the best. For example, the lower one is more representative of the Antarctic measurements, the top one of mid northern latitudes, and so on.

The important points associated with these scenerios and the data are:

- Scenerio C from Hansen, et al. was a good model for the actual CH4 mixing ratios for about a decade.

- Scenerios A and B were overestimates for methane forcing

- Beyond 2005, even Scenerio C is beginning to exceed actual mixing ratios.

- Claims by Michaels that actual emissions followed Scenerio A are falsified for both CO2 and CH4. At best Michaels is culpable for not RTFR. At worst he is a stone liar and a perjurer.

- Those attempting to defend Michaels have either not RTFR, or cannot UTFR or are just passing gas.

- Comparison of trends in greenhouse gas emissions with these predictions show that alternative scenerios such as those proposed by Hansen are possible.

- Most importantly it shows that reasonable scenerios can be constructed over a ~20 year period (contrast that with economics for example).

- It shows that many details in emission scenerios are unimportant, or rather that false estimates in one direction are most likely going to be cancelled by false estimates in the other for a different forcing agent, and that on average the scenerios should be useful for larger periods.