Global Warming Contribution

Figure 3 gives the relative contribution to global warming caused by different chemical species, with an assumed 100-year time horizon and 1990 emissions estimates.

Carbon dioxide, with its enormous annual increase in concentration, contributes most, at 61%. Methane is second in importance, at 15%, CFC-12 is third, contributing 7%, and nitrous oxide fourth with 4% of the warming under these assumptions. If we took the 500-year horizon, the percentages would change, with longer-lived species contributing larger percentages.

The question now is how do we estimate future emissions of greenhouse gases? Past trends can be used as a starting point, but future emissions will be determined by a complex combination of economic, regulatory, and societal factors. Some, like the CFCs, can be changed relatively quickly by switching to different chemicals for certain industrial and manufacturing processes and consumer products (e.g., eliminating Styrofoam cups that use CFCs). Others like the burning of fossil fuels cannot be changed very quickly, even if society chooses to do so (it takes many years to put a nuclear power plant in operation to replace a coal-fired plant). Since no one can predict the future with any certainty, we resort to considering several different scenarios, each of which gives a specific set of assumptions on economic, political, and social factors.

PREVIOUS: Atmospheric Lifetime and GWP Compared to CO₂

NEXT: Different Future Socio-Economic Development Paths