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contribution of each major factor to the current uncertainty 

 of sea level rise from thermal expansion, using the low scenario 

 as a baseline. Assumptions were changed one-at-a-time from 

 low to high for each factor. The first four factors (CO2 

 emissions, chlorof luorocarbons , nitrous oxide, and methane) 

 were approximately additive in their effects. Because the 

 other factors were not, changing them in a different order 

 would change these estimates somewhat. Nevertheless, this 

 figure conveys the relative importance of the uncertainties 

 for each of the various factors in 25-year time spans. 



This figure reveals some important insights for setting 

 research priorities. The best way to improve estimates of sea 

 level rise to the year 2025 would be to improve estimates of 

 temperature (climate) sensitivity, and next, the concentrations 

 of the trace gases. In the longer term, the level of CO2 becomes 

 quite important. 



The atmospheric fraction airborne for CO2 and diffusivity 

 do not appear to be the major sources of uncertainty. It is 

 possible that increasing temperatures may stratify the ocean, 

 and increase fraction airborne and decrease diffusivity beyond 

 the ranges of our assumptions. However, although these effects 

 would both raise atmospheric temperatures, their effects on sea 

 level rise would tend to offset one another. 



Appendix A shows that in the long run, the impact of 

 extreme and unexpected forms of natural variation (volcanoes 

 and solar radiation) are unlikely to be important, except in 

 the early stages when they could mask the overall trend. 



