How much warming are we committed to and how much can be avoided

摘要: This paper examines different concepts of a ‘warming commitment’ which is often used in various ways to describe or imply that certain level warming irrevocably committed over time frames such as the next 50 100 years, longer. We review and quantify four concepts, namely (1) ‘constant emission commitment’, (2) ‘present forcing (3) a‘zero (geophysical) (4) ‘feasible scenario commitment’. While probably most relevant one for policy making, it depends centrally on key assumptions technical, economic political feasibility future greenhouse gas reductions. issue direct relevance when considers 2002 global mean temperatures were 0.8± 0.2 ∘C above pre-industrial (1861–1890) European Union has stated goal limiting 2 mean: What risk we are overshoot ∘C? Using simple climate model (MAGICC) probabilistic computations based conventional IPCC uncertainty range sensitivity (1.5 4.5 ∘C), found constant virtually with central estimate 2.0 by 2100 (4.2 2400). For present radiative levels seems unlikely overshoot. (central 1.1 1.2 2400 ∼10% probability overshooting ∘C). However, increasing rapidly if stabilized much 400 ppm CO2 equivalence (1.95 W/m2) long-term. From geophysical point view, all human-induced emissions ceased tomorrow, ‘exceptionally unlikely’ will be estimate: 0.7 2100; 0.4 Assuming according lower end published mitigation scenarios (350 CO2eq 450 CO2eq) provides temperature projections 1.5 2.1 2400) between 10 50% 1–32% equilibrium. Furthermore, ‘avoidable warming’ 0.16–0.26 every GtC avoided – scenarios.