20. Projected anthropogenic CO2 emissions from fossil fuel use, deforestation and cement production are shown for some of the IPCC emission scenarios. The highest emission scenario - IS92e - assumes moderate population growth, high economic growth, high fossil fuel availability, and a phase out of nuclear power; and the lowest emission scenario - IS92c - assumes low population growth, low economic growth, and severe constraints on fossil fuel supplies.
Understanding how CO2 concentrations in the atmosphere will change in the future requires carbon cycle models which model the relationship between emissions and atmospheric concentrations. The estimated CO2 concentration in the atmosphere for each emission scenario (calculated using the Bern model) is shown in the second figure. All scenarioes show increased concentrations that are well above pre-industrial levels by 2100 (75 to 220% higher).
Climate induced environmental changes cannot be reversed quickly. Even if the anthropogenic emissions of CO2 are stabilized or reduced, the CO2 content in the atmosphere will still increase for some time.