Stabilization of atmospheric carbon dioxide via zero emissions--an alternative way to a stable global environment. Part 1: examination of the traditional stabilization concept.

The concept of "stabilization" of atmospheric CO(2) concentration is re-examined in connection with climate-change mitigation strategies. A new "zero-emissions stabilization (Z-stabilization)" is proposed, where CO(2) emissions are reduced to zero at some time and thereafter the concentration is decreased by natural removal processes, eventually reaching an equilibrated stable state. Simplified climate experiments show that, under Z-stabilization, considerably larger emissions are permissible in the near future compared with traditional stabilization, with the same constraint on temperature rise. Over longer time scales, the concentration and temperature decrease close to their equilibrium values, much lower than those under traditional stabilization. The smaller temperature rise at final state is essential to avoid longer-term risk of sea level rise, a significant concern under traditional stabilization. Because of these advantages a Z-stabilization pathway can be a candidate of practical mitigation strategies as treated in Part 2.

Stabilization of atmospheric carbon dioxide via zero emissions--an alternative way to a stable global environment. Part 2: a practical zero-emissions scenario.

Following Part 1, a comparison of CO(2)-emissions pathways between "zero-emissions stabilization (Z-stabilization)" and traditional stabilization is made under more realistic conditions that take into account the radiative forcings of other greenhouse gases and aerosols with the constraint that the temperature rise must not exceed 2 °C above the preindustrial level. It is shown that the findings in Part 1 on the merits of Z-stabilization hold under the more realistic conditions. The results clarify the scientific basis of the policy claim of 50% reduction of the world CO(2) emissions by 2050. Since the highest greenhouse gas (GHG) concentration and temperature occur only temporarily in Z-stabilization pathways, we may slightly relax the upper limit of the temperature rise. We can then search for a scenario with larger emissions in the 21st century; such a scenario may have potential for practical application. It is suggested that in this Z-stabilization pathway, larger emissions in the near future may be important from a socioeconomic viewpoint.