Mid- and long-term climate projections for fragmented and delayed-action scenarios

摘要: Abstract This paper explores the climate consequences of “delayed near-term action” and “staged accession” scenarios for limiting warming below 2 °C. The stabilization greenhouse gas concentrations at low levels requires a large-scale transformation energy system. Depending on policy choices, there are alternative pathways to reach this objective. An “optimal” path, as emerging from energy-economic modeling, implies immediate action with stringent emission reductions, while currently proposed international policies translate into reduction delays higher emissions. In our delayed scenarios, need thus be reached comparatively high 2030 levels. Negative economic cost explored in accompanying papers significantly mid-term warming, indicated by rate 50% 2040s. By contrast, both mid- long-term another class staged accession that lets some regions embark others follow later, conservation carbon-price comparable optimal scenarios. Not only is cases, but probability exceed 2 °C 21st century increases factor 1.5.