Abstract
We assessed how projected changes in the physical Southern Ocean will alter population trajectories of the two pack-ice penguins of the Antarctic, the Emperor (Aptenodytes forsteri) and Adélie (Pygoscelis adeliae). Using a subset of IPCC AR4 climate model output for emission scenario SRES A1B (doubling of CO2 from 360 and stabilizing at 720 after 2100), we identify the time period at which global temperature will have increased by 2°C above pre-industrial levels. Using this benchmark, rather than an arbitrary year, allowed removal of some of the biases and uncertainties associated with the differing model sensitivities. We, then, for the Antarctic, considered criteria and identified a subset of the “better” IPCC AR 4 climate model outputs. The “best” four — GFDL-CM2.1, GFDL-CM2.0, MIROC3.2(hires), and MRI-CGCM2.3.2a — were composited into an ENSEMBLE, which was then examined to look at conditions at the year of 2°C warming. Care was taken to evaluate the individual models that comprise the ENSEMBLE, as errors in different models tend to cancel one another often leading to an unjustified faith in the collective predictions. The ENSEMBLE output provided indicators of sea-ice coverage, wind speeds, and air temperatures for the Southern Ocean. These indicators of physical conditions were then used to assess the impacts of a 2°C global warming on penguins’ habitat and ultimately their populations. On the basis of the ENSEMBLE output, we concluded that 50% of Emperor colonies (40% of population) and 75% of Adélie colonies (70% of population) that currently exist at latitudes north of 70°S are in jeopardy of marked decline or disappearance, largely because of severe decreases in pack-ice coverage and, particularly for Emperors, ice thickness as well (especially in the eastern Ross and Weddell seas). Included are colonies on both sides of the northern Antarctic Peninsula and in East Antarctica.
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