Business was not usual (continued)
Jim Hansen, in his testimony to the Senate Committee on Energy and Natural Resources (btw he testified four times on essentially the same topic between November 1987 and 1989) said:
For the future, it is difficult to predict reliably how trace gases will continue to change. In face, it would be useful to know the climatic consequences of althernative scenerios. So we have considered three scenarios for future trace gas growth, shown on the next viewgraph.Of course, as we have seen in the previous post, atmospheric methane (CH4) concentrations have leveled off starting in 1990 and the Montreal Protocols are actually reducing the mixing ratios of the CFCs.
Scenerio A assumes the CO2 emissions will grow 1.5 percent per year and that CFC emissions will grow 3 percent per year. Scenerio B assumes constant future emissions. If populations increase, Scenerio B requires emissions per capita to decrease.
Scenerio C has drastic cuts in emissions by the year 2000, with CFC emissions eliminated entirely and other trace gas emissions reduced to a level where they just balance their sinks.
These scenarios are designed specifically to cover a very broad range of cases. If I were forced to choose one of these as most plausible, I would say Scenario B. My guess is that the world is now probably following a course that will take it somewhere between A and B
In testimony to the House Energy and Power Subcommittee Hansen made the following recommendations for immediate action:
I think we could take some steps now to reduce the rate of growth of the greenhouse effect. Chlorofluorocarbons, which destroy ozone, as well as cause 20 percent of the greenhouse effect, could be phased out entirely over an appropriate period of time. The manufacturers agree that there are or will be substitutes for the chlorofluorocarbons.Before anyone gets crazy, the "CO2 causes 55-60 percent of the greenhouse effect", clearly refers to the forcing, not the total greenhouse effect.
Also, we should increase our energy efficiency, because CO2 causes 55-60 percent of the greenhouse effect. There's a lot of room for improved efficiency. It would have other benefits, independent of the greenhouse effect, especially on our balance of payments deficit. How to get at that problem is, of course, a major difficulty and that's something you can address better than I can. I know that there are major ways that we could improve our energy efficiency.
Finally, I think we should discourage deforestation and encourage reforesetation, because that would not only reduce atmospheric CO2, but also preserve the habitat for innumerable, valuable biological species. The impact of these kinds of steps on the short run is going to be relatively small, but it's very important, because it would change the direction in which the greenhouse effect is headed. Instead of the sharp, upward ramp that we're on now, it could put us on a more manageable course on the longer term, over the next several decades.