Consequences of twenty-first century policy for multi-millennial climate and sea-level change

1 There is scientific consensus that unmitigated carbon emissions will lead to global warming of at least several degrees Celsius by 2100 (ref. 1), resulting in high-impact local, regional, and global risks to human society and natural ecosystems2. Despite this consensus, international efforts to address the challenge of global climate change have been and remain limited in scope3. We suggest that one important factor contributing to this impasse is the focus of the scientific community on near-term climate changes and their uncertainties. In particular, the scientific emphasis on the expected climate changes by 2100, which was originally driven by past computational capabilities, has created a misleading impression in the public arena — the impression that human-caused climate change is a twenty-first-century problem, and that post-2100 changes are of secondary importance, or may be reversed with emissions reductions at that time. Socioeconomic and policy discussions regarding climate change have also focused primarily on near-term impacts to the end of this century. The viewpoint that the near term is the most relevant timeframe with regard to socioeconomic impacts and adaptation reflects an implicit discounting of future impacts, as well as an assumption that successful mitigation measures could reverse the negative impacts of climate change over the next few hundred years. Consequences of twenty-first century policy for multi-millennial climate and sea-level change