Thursday, June 01, 2006

Scenerio A B and C

Having posted on Hansen et al., assumptions for CO2 forcing, it struck me that there was some value in posting the scenerios for the other gases. Might even get others to do some of the work.

CH4

A: Begins at 1.4 ppbV in 1958. Increases by 0.06%/yr until 1970, 1%/yr until 1980 and 1.5%/yr thereafter.

B. Begins at 1.4 ppbV in 1958. Increases by 0.06%/yr until 1970, 1%/yr until 1980, 1.5%/yr until 1990, 1%/yr until 2000 and 0.5%/yr thereafter

C. Begins at 1.4 ppbV in 1958. Increases by 0.06%/yr until 1970, 1%/yr until 1990, 0.5%/yr until 1990, 1%/yr until 2000 and is constant thereafter.

Amazingly, the data most closely matches scenerio C. Methane concentrations level off ~1990 so all scenerios overestimate methane concentrations. Scenerio A is wildly off. This is a serious problem for anyone trying to claim that Scenerio A is the McGuffin.
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CFCs (principally CFC-11 and 12) . Note: the scenerios look at emissions not concentrations. CFC lifetimes are assumed to be 75 and 150 years

A: Data ends in 1982. Emissions are assumed to increase at a rate of 3%/yr.

B. Data ends in 1982. Emissions increase at a 3%/yr until 1990, 2% until 2000, 1% until 2010 and are constant thereafter.

C. Data ends in 1982. Emissions increase at a 3%/yr until 1990 and then decrease linearly to zero.

The problem with interpreting this is that while C best approximated what happened with CFCs, the HFCs that were introduced in their stead have a significant greenhouse potential. This would have to be factored in. The Scenerios model increases in other CFC like molecules by multiplying the CFC forcing by two.
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N2O

A: Increases 0.1% from 1958, 0.2% from 1980, 0.4% from 2000 and 0.9% in 2030

B. Defined differently (weird) Uses a formula that depends on anthropogenic emissions which are assumed to start at a 3.5%/yr growth rate in 1988, decline to 2.5%/yr in 1990, 1.5% in 2000 and 0.5% in 2010.

C. Flat lines after 1988.

I have to RTFRs to get beyond this to concentrations and forcings, but it is clear that Scenerio A is an overestimate for the actual forcings since 1988.

2 comments:

Tim Lambert said...

N2O emissions in scenario A grow by 3.5% per year. The description is confusing 'cos it's talking about the growth of concentration rather tahn emissions. I had to check the cited reference before I figured out what was going on.

EliRabett said...

Tim: The unnecessary confusion is that Hansen et al. stated the N2O growth differently for Scenerios A and C (concentrations) than for B (emissions). I have the reference now and will be doing N2O next. The methane concentrations for the various scenerios and the the data is now posted.