Anthropogenic forcing dominates global mean sea-level rise since 1970

摘要

Sea-level change is an important consequence of anthropogenic climate change, as higher sea levels increase the frequency of sea-level extremes and the impact of coastal flooding and erosion on the coastal environment, infrastructure and coastal communities(1,2). Although individual attribution studies have been done for ocean thermal expansion(3,4) and glacier mass loss(5), two of the largest contributors to twentieth-century sea-level rise, this has not been done for the other contributors or total global mean sea-level change (GMSLC). Here, we evaluate the influence of greenhouse gases (GHGs), anthropogenic aerosols, natural radiative forcings and internal climate variability on sea-level contributions of ocean thermal expansion, glaciers, ice-sheet surface mass balance and total GMSLC. For each contribution, dedicated models are forced with results from the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model archive(6). The sum of all included contributions explains 74 +/- 22% (+/- 2 sigma) of the observed GMSLC over the period 1900-2005. The natural radiative forcing makes essentially zero contribution over the twentieth century (2 +/- 15% over the period 1900-2005), but combined with the response to past climatic variations explains 67 +/- 23% of the observed rise before 1950 and only 9 +/- 18% after 1970 (38 +/- 12% over the period 1900-2005). In contrast, the anthropogenic forcing (primarily a balance between a positive sea-level contribution from GHGs and a partially offsetting component from anthropogenic aerosols) explains only 15 +/- 55% of the observations before 1950, but increases to become the dominant contribution to sea-level rise after 1970 (69 +/- 31%), reaching 72 +/- 39% in 2000 (37 +/- 38% over the period 1900-2005).