melting of this ice could raise ocean levels by more than 50 m. Even a partial melting could have a pronounced effect on seashore areas. However, the mechanisms for this melting process are not well understood, and thus the rate of melting cannot be predicted. It is expected that the melting process due to warmer air would be extremely slow. A more important event would be that warm polar waters would cause a flow of ice from the continental shelves into the open seas, possibly raising the sea level by several meters in 300 years. 2.3.5 Possible Mitigating Measures Should it be well established that increasing atmospheric CO2 levels will produce serious environmental threats, there are several options open to counteract the problem. The most obvious is a switch from fossil fuels to alternative energy sources. However, the lead time required for such a switch could be considerable, and new technologies may entail environmental problems of their own. Another option would be to increase the biospheric sink for CO2 by planting more trees. Doubling the mass of living trees would store about 3 x 10^-2 t of carbon, which is between a third and a sixth of what might otherwise accumulate in the atmosphere from fossil fuel combust ion. This would have a significant mitigating effect, but would be almost impossible to accomplish within the time frame in which large impacts could occur. Furthermore, trends in forest cover are currently going in the other direction due to population increases and needs for forest resources. Removal of CO2 emissions from major sources is a possibility, although a costly one, as yet unproven, and quite likely energy-inefficient. Other potential mitigating techniques include fertilizing the oceans to accelerate oceanic uptake of C02«^^ Other forms of human intervention are possible. The addition of aerosols over oceans might act to counterbalance the greenhouse effect. Increasing the surface albedo by some means could reduce the amount of solar energy absorbed in the earth-atmosphere system. The actual result of some of these mitigation strategies is only speculative. The only option that would appear to be immediately available would be a curtailment in the use of fossil fuels, but given the global nature of the CO2 issue, any action along these lines could not be taken by the United States alone but would require the cooperation of all nations.
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