From the analysis presented in this paper, temperature emerges as the key control 

 on sea level. It directly controls steric water expansion and the mass balance of the 

 polar ice sheets. It indirectly controls global surface- and groundwater budgets. The 

 global mean temperature record over the last century can best be explained in terms of 

 the combined effects of natural climatic cycles and a warming trend from addition of 

 CO7 to the atmosphere ("greenhouse effect") due to the burning of fossil fuels (Broecker 

 1975). 



An extension of Broecker's analysis has been made in Figure 5 with temperature 

 data updated through 1980 and the model of Hansen et al. (1981) used as a basis for the 

 predicted C02-related warming trend. The figure demonstrates that observed 

 temperatures essentially fall within the range predicted from the two component trends 

 for most of the century. Global temperatures over the last few years, however, have 

 risen significantly above the predicted trend. 



"le natural temperature cycles used in this analysis are based on analysis of stable 

 ; (0) in ice cores from Camp Century in Greenland (Dansgaard et al. 1971). 



Thf 

 isotopes 



Whatever the origin of the climatic cycles observed in the Greenland ice cores, the 

 pattern has been essentially stable during the last 1,000 years. Two cycles appear to be 

 inherent in the Camp Century temperature record, one of 80-year and another of 180- 

 year duration. The curve in Figure 5 is the composite of these two cycles. Because of 

 the regular harmonic pattern this natural temperature curve can easily be extended and 

 thus provide one element in the predicton of future global temperature trends. 



It is well documented that the COn 

 steadily increasing in this century (Si 

 modelling of the atmospheric response to 

 Wetherald (1975) and Hansen et al. (198! 

 in the atmosphere from "pre-industrial" 

 increase global temperatures by 2.4°C to 

 atmospheric CO2 content because this 

 throughout the world. 



content of the terrestrial atmosphere has been 

 egenthaler and Oeschger 1978). Numerical 

 an increase in its COt contents by Manabe and 

 ) suggested that a doubling of the CO2 content 



levels of about 300 ppm to 600 ppm would 

 3.5°C. A major unknown, is the rate of rise of 



is largely controlled by industrial patterns 



Natural Cycles 



Observed Globol Mean 



COj Worming 



Predicted Temperature Trend 



1900 

 Year 



Figure 5. Global temperature variations. The predicted temperature trend 

 is the composite of that due to C02-induced warming and natural temperature 

 cycles. Observed global temperatures and predicted COp warming from Hansen 

 et al . (1981). Figure design modeled after Broecker (1975), 



169 



