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doubles, the earth's total equilibrium temperature increase 

 is likely to be between 3°C to 9°C (5.4°F to 16.2°F). 



CONCENTRATIONS OF GREENHOUSE GASES WILL ALMOST CERTAINLY DOUBLE 

 IN THE NEXT CENTURY 



In the past 180 years, atmospheric CO2 appears to have 

 risen approximately 20 percent, from between 260 and 290 ppm 

 to 340 ppm. Very accurate monitoring began in 1958; since then, 

 atmospheric CO2 has increased 8 percent, from 315 ppm to 

 340 ppm._^/ 



Atmospheric levels of other gases have also risen. Methane 

 increased annually by about 1 to 2 percent from 1970 to 1980, 

 chlorof luorocarbons by about 6 percent over the same period, 

 and nitrous oxide by about 0.2 percent per year from 1975 

 to 1980. V 



Economic activities have caused most of these increases. 

 For CO2, the most important cause of emissions has been the 

 combustion of oil, gas, and coal, with deforestation probably 

 contributing a small percentage. Burning fossil fuels (hydro- 

 carbons) oxidizes carbon ( C + 20 -> CO2 ) , inevitably 

 releasing CO2. 



Future energy use and fuel selection will thus be the 

 primary determinants of the rate of CO2 emissions. Because 

 fossil fuels have important competitive advantages and play a 

 critical role in existing energy systems, their use is expected 

 to grow even if radical policies are undertaken to curtail their 

 use. For example, Seidel and Keyes found that even a 300 percent 

 worldwide tax on fossil fuel use would delay a 2°C temperature 



