3. The transfer of heat to the deep ocean occurs more slowly than the transfer of heat within the atmosphere or within the upper layers of the ocean. The resulting transient period, or ''lag," means that the global average surface temperature at any time is lower than the temperature that would prevail after all the redistribution had been completed. The greater the response, the faster the warming; however, the increase in the warming rate is less than proportional to the climate sensitivity, so it will take longer for the full warming to appear. At the time of equivalent CO2 doubling, for example, the global average surface temperature may be as little as one-half the ultimate equilibrium temperature associated with those concentrations.
4. A rise in sea level may accompany global warming, possibly in the range of 0 to 60 cm (0 to 24 inches) for the temperature range listed above. This range allows for uncertainties in estimates of current sea level change. Zero is included in the range not only because of the uncertainties but also because precipitation in the Antarctic functions to partially offset thermal expansion.
5. A wide range of potentially amplifying or moderating feedbacks have been suggested that involve atmospheric composition and climatic changes. Examples include increased CH4 emissions as the permafrost melts, increased carbon uptake by plants at higher CO2 concentrations, increased summer drying of continental interiors, increased continental precipitation in winter, increased hurricane frequency and/or intensity, and many more potential changes and surprises. Convincing quantitative demonstrations and confirmations of these and other potential changes are lacking, and there is no evidence that any of the changes are imminent, but none of them are precluded.