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The lapse rate feedback is the dominant driver of stronger warming in the Arctic than the Antarctic in simulations with increased CO2. While Antarctic surface elevation has been implicated in promoting a weaker Antarctic lapse rate feedback, the mechanisms in which elevation impacts the lapse rate feedback are still unclear. Here we suggest that weaker Antarctic warming under CO2 forcing stems from shallower, less intense climatological inversions due to limited atmospheric heat transport above the ice sheet elevation and elevation‐induced katabatic winds. In slab ocean model experiments with flattened Antarctic topography, stronger climatological inversions support a stronger lapse rate feedback and annual mean Antarctic warming comparable to the Arctic under CO2 doubling. Unlike the Arctic, seasonality in warming over flat Antarctica is mainly driven by a negative shortwave cloud feedback, which exclusively dampens summer warming, with a smaller contribution from the winter‐enhanced lapse rate feedback. Plain Language Summary: Models project stronger surface warming in the Arctic than the Antarctic under climate change. A climate feedback in which more warming occurs near the surface than at higher altitudes in the atmosphere promotes this stronger Arctic warming. Antarctica's surface elevation is thought to weaken this feedback in comparison to the Arctic, but how this occurs is unclear. Here we show that Antarctic elevation weakens surface warming by changing the base state vertical temperature structure. When Antarctic topography is flattened in model experiments, Antarctica experiences more warming under climate change, resembling Arctic warming. Similarly to the Arctic, flat Antarctica warms most during the winter, but this seasonality is driven by different climate feedbacks in the Arctic versus Antarctic. These results indicate the importance of base state temperatures for warming under climate change and suggest that strong polar amplification is possible without local sea ice loss. Key Points: Antarctic elevation causes asymmetry in climatological inversions, lapse rate feedbacks, and warming between the polesIn model experiments with flattened Antarctica, strengthened inversions lead to stronger lapse rate feedback and Antarctic amplificationShortwave cloud feedback promotes seasonality in flat Antarctic warming; lapse rate feedback more strongly promotes seasonality in Arctic [ABSTRACT FROM AUTHOR]

A coupled global climate model is used to evaluate processes that determine the equilibrium location of the sea-ice edge and its climatological annual cycle. The extent to which the wintertime ice edge departs from a symmetric ring around either pole depends primarily on coastlines, ice motion, and the melt rate at the ice–ocean interface. At any location the principal drivers of the oceanic heat flux that melts sea ice are absorbed solar radiation and the convergence of heat transported by ocean currents. The distance between the ice edge and the pole and the magnitude of the ocean heat flux convergence at the ice edge are inversely related. The chief exception to this rule is in the East Greenland Current, where the ocean heat flux convergence just east of the ice edge is relatively high but ice survives due to its swift southward motion and the protection of the cold southward-flowing surface water. In regions where the ice edge extends relatively far equatorward, absorbed solar radiation is the largest component of the ocean energy budget, and the large seasonal range of insolation causes the ice edge to traverse a large distance. In contrast, at relatively high latitudes, the ocean heat flux convergence is the largest component and it has a relatively small annual range, so the ice edge traverses a much smaller distance there. When the model is subject to increased CO2 forcing up to twice preindustrial levels, the ocean heat flux convergence weakens near the ice edge in most places. This weakening reduces the heat flux from the ocean to the base of the ice and tends to offset the effects of increased radiative forcing at the ice surface, so the ice edge retreats less than it would otherwise. [ABSTRACT FROM AUTHOR]

Submarine measurements of sea ice draft show that the ice has thinned in some parts of the Arctic Ocean at a remarkably high rate over the past few decades. The spatial pattern indicates that the thinning was a strong function of ice thickness, with the greatest thinning occurring where the ice was initially thickest. A similar relationship between sea ice thinning and the initial thickness is reproduced individually by three global climate models in response to increased levels of carbon dioxide in the models' atmosphere. All three models have weak trends in their surface winds and one model lacks ice dynamics altogether, implying that trends in the atmosphere or ice circulation are not necessary to produce a relatively high rate of thinning over the central Arctic or a thickness change that increases with the initial thickness. A general theory is developed to describe the thinning of sea ice subjected to climate perturbations, and it is found that the leading component of the thickness dependence of the thinning is due to the basic thermodynamics of sea ice. When perturbed, sea ice returns to its equilibrium thickness by adjusting its growth rate. The growth-thickness relationship is stabilizing and hence can be reckoned as a negative feedback. The feedback is stronger for thinner ice, which is known to adjust more quickly to perturbations than thicker ice. In addition, thinner ice need not thin much to increase its growth rate a great deal, thereby establishing a new equilibrium with relatively little change in thickness. In contrast, thicker ice must thin much more. An analysis of a series of models, with physics ranging from very simple to highly complex, indicates that this growth-thickness feedback is the key to explaining the models' relatively high rate of thinning in the central Arctic compared to thinner ice in the subpolar seas. [ABSTRACT FROM AUTHOR]

The Northern Hemisphere polar amplification of climate change is documented in models taking part in the Coupled Model Intercomparison Project and in the new version of the Community Climate System Model. In particular, the magnitude, spatial distribution, and seasonality of the surface warming in the Arctic is examined and compared among the models. The range of simulated polar warming in the Arctic is from 1.5 to 4.5 times the global mean warming. While ice-albedo feedback is likely to account for much of the polar amplification, the strength of the feedback depends on numerous physical processes and parametrizations which differ considerably among the models. Nonetheless, the mean sea-ice state in the control (or present) climate is found to influence both the magnitude and spatial distribution of the high-latitude warming in the models. In particular, the latitude of the maximum warming is correlated inversely and significantly with sea-ice extent in the control climate. Additionally, models with relatively thin Arctic ice cover in the control climate tend to have higher polar amplification. An intercomparison of model results also shows that increases in poleward ocean heat transport at high latitudes and increases in polar cloud cover are significantly correlated to amplified Arctic warming. This suggests that these changes in the climate state may modify polar amplification. No significant correlation is found between polar amplification and the control climate continental ice and snow cover. [ABSTRACT FROM AUTHOR]