Updated
12 October, 2003
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US
National Assessment of |
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Figure 11: Projections
of the Intergovernmental Panel on Climate Change for the CO2 concentration
over the next 100 years (IPCC 1992). The red line gives the preferred, Business-as-Usual
estimate used in this study while the other lines show how the 1% equivalent
CO2 compares to IS92a equivalent CO2 and IS92a CO2. The blue line shows
IS92a sulfur emissions. The updated emissions scenarios being provided by
IPCC in preparation for its year 2000 assessment would not significantly
affect the overall range of the possible concentration scenarios for the
21st century. Both HadCM2 and CGCM1 do not use multiple greenhouse
gases, so that the radiative effects of all the greenhouse gases are incorporated
into a larger CO2 concentration (so-called equivalent CO2). The actual
scenario used is 1% per year compounded increase in CO2 after 1990.
The actual IS92a CO2 value (in pink curve below) is 353.6 ppmv, while the
equivalent CO2 value at 1990 is 409.66. The final CO2 value
at 2100 is 705.4 ppmv for IS92a CO2 alone, 1021.77 ppmv for IS92a equivalent
CO2 with the SAR radiative forcing and 1408.95 with the HadCM2 radiative
forcing, and 1346.09 for the 1% increase in CO2. IS92a sulfur
emissions are twice present-day values by 2100. The concentration/emission
values were calculated from the radiative forcing values of SAR IS92a, supplied
by Tom Wigley. I used the formulas in Appendix 2 of IPCC Technical
Paper II to convert from radiative forcing to concentrations/emissions.
The SAR conversion factor is 6.3 while the HadCM2 conversion factor is 5.05.
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