ALBERT

Description: Increasing concentrations of greenhouse gases are the primary contributor to the 0.8 °C increase in the global average temperature since the late 19th century, shortening cold seasons and lengthening warm seasons. The warming is amplified in polar regions, causing retreat of sea ice, snow cover, permafrost, mountain glaciers, and ice sheets, while also modifying mid-latitude weather, amplifying global sea level rise, and initiating high-latitude carbon feedbacks. Model simulations in which we reduced solar insolation over high latitudes not only cooled those regions, but also drew energy from lower latitudes, exerting a cooling influence over much of the hemisphere in which the reduction was imposed. Our simulations, which used the National Center for Atmospheric Research's CAM3.1 atmospheric model coupled to a slab ocean, indicated that, on a normalized basis, high-latitude reductions in absorbed solar radiation have a significantly larger cooling influence than equivalent solar reductions spread evenly over the Earth. This amplified influence occurred because high-latitude surface cooling preferentially increased sea ice fraction and, therefore, surface albedo, leading to a larger deficit in the radiation budget at the top of the atmosphere than from an equivalent global reduction in solar radiation. Reductions in incoming solar radiation in one polar region (either north or south) resulted in increased poleward energy transport during that hemisphere's cold season and shifted the Inter-Tropical Convergence Zone (ITCZ) away from that pole, whereas equivalent reductions in both polar regions tended to leave the ITCZ approximately in place. Together, these results suggest that, until emissions reductions are sufficient to limit the warming influence of greenhouse gas concentrations, polar reductions in solar radiation, if they can be efficiently and effectively implemented, might, because of fewer undesirable side effects than for global solar radiation reductions, be a preferred approach to limiting both high-latitude and global warming.

Description: With human-induced climate change leading to amplified warming in high latitudes, mitigation alone is unlikely to be rapid enough to prevent significant, even irreversible, impacts. Model simulations in which solar insolation was arbitrarily reduced poleward of 51, 61, or 71° latitude in one or both hemispheres not only cooled those regions, but also drew energy from lower latitudes, exerting a cooling influence over much of the particular hemisphere in which the reduction was imposed. The simulations, conducted using the National Center for Atmospheric Research's CAM3.1 atmospheric model coupled to a slab ocean, indicated that high-latitude reductions in absorbed solar radiation have a significantly larger cooling influence than solar reductions of equivalent magnitude spread evenly over the Earth. This amplified influence occurred primarily because concentrated high-latitude reductions in solar radiation led to increased sea ice fraction and surface albedo, thereby amplifying the energy deficit at the top of the atmosphere as compared to the response for an equivalent reduction in solar radiation spread evenly over the globe. Reductions in incoming solar radiation in one polar region (either north or south) resulted in increased poleward energy transport during that hemisphere's cold season and shifted the Inter-Tropical Convergence Zone (ITCZ) away from that pole, whereas comparable solar reductions in both polar regions resulted in increased poleward energy transport, but tended to leave the ITCZ approximately in place. Together, these results suggest that, until emissions reductions are sufficient to limit the warming influence of increasing greenhouse gas concentrations, polar reductions in solar radiation, if they could be efficiently and effectively implemented, warrant further research as an approach to moderating the early stages of both high-latitude and global warming.