The concept of “stabilization” of atmospheric CO₂ concentration is re-examined in connection with climate-change mitigation strategies. A new “zero-emissions stabilization (Z-stabilization)” is proposed, where CO₂ 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.

(Contributed by Taroh MATSUNO, M.J.A.)