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Sea surface temperature (SST) observations in the North Atlantic since 1870 reveal a region of enhanced warming off the northeastern coast of North America, and a region of cooling to the south of Greenland. It has been hypothesized that these adjacent SST trends are a result of long‐term changes in the buoyancy‐driven ocean circulation—a slowdown of the Atlantic Meridional Overturning Circulation. The impacts of these historical SST trends on the atmosphere are estimated using idealized atmospheric general circulation model experiments in which the global atmosphere is exposed to modern climatological forcing minus the aforementioned regional SST trends. The local response includes a negative North Atlantic Oscillation tendency and southward shift of the wind forcing for the subtropical gyre. Due to planetary wave propagation, the regional SST trends also induce a northward shift of the intertropical convergence zone over the Indian Ocean. Implications for climate feedbacks and projections are discussed. Plain Language Summary: The ocean surface is warming over most of the planet, with a couple of notable exceptions. One is over the North Atlantic Ocean, just south of Greenland, where the temperature of the ocean surface has actually been cooling by about 1°C since 1870. Nearby, extending off the northeastern coastline of North America is a region where the ocean surface has been warming much faster than the global ocean on average—by about 1.5°C since 1870. This side‐by‐side pair of accelerated warming and cooling trends is likely due to a slowdown of the ocean's overturning circulation, which carries large amounts of heat energy from the tropics toward the poles. This paper reveals the effects of those unusual ocean temperature trends in the North Atlantic on the atmospheric circulation using a computer model of the global atmosphere. The model simulations indicate that these ocean temperature trends are causing shifts in the jet stream, changing the way the winds propel the upper ocean currents, and even have impacts quite far away by moving the tropical rain belt northward in the Indian Ocean. Key Points: The impact of historical sea surface temperature trends in the North Atlantic since 1870 is simulated with a global atmospheric modelAdjacent warming and cooling trends in the North Atlantic Ocean induce a negative NAO‐like response and southward‐shifted gyre forcingPropagation of planetary waves away from the North Atlantic induces a northward‐shifted intertropical convergence zone in the Indian Ocean [ABSTRACT FROM AUTHOR]

We report 20 10Be exposure ages from glacial erratics and bedrock on the west coast of British Columbia, Canada, which add to existing chronologies of Cordilleran Ice Sheet retreat along ∼600 km of coastal North America. Collectively, these data show the western ice limit reached the present coast by 18–16 ka then retreat slowed for ∼4,000 years until 14–13 ka. We attribute initial retreat to destabilization and grounding line retreat resulting from rising sea level and/or ocean warming in the northern Pacific. Subsequent stability of the ice sheet at the present coastal margin was likely due to the transition from marine to terrestrial margins despite increasing temperatures that may have driven ice sheet thinning. Our findings demonstrate the importance of understanding both climatic and nonclimatic drivers of ice sheet change through time. Plain Language Summary: The Cordilleran Ice Sheet once covered western North America and was similar in size and characteristics to the modern Greenland Ice Sheet. It is therefore a good analog for how the Greenland Ice Sheet may respond to changing climate and underlying topography in the future. We show the western margin of the Cordilleran Ice Sheet retreated rapidly from around 18,000 years ago but then stabilized for several thousand years close to the present coastline. Ice may still have been lost during this period of relative stability, but through vertical thinning rather than lateral retreat, demonstrating the importance of understanding ice sheets in three‐dimensions. Our reconstruction shows that atmospheric and oceanic temperatures and underlying topography can all control ice sheet stability. We also show that hundreds of kilometers of coastline were free of ice prior to an important period of early human migration into the Americas. Key Points: Consistent, western ice sheet margin retreat at ∼18–16 ka driven by destabilization due to sea level rise and/or ocean warmingRetreat stabilized during ∼17–13 ka after reaching present coastIce sheet margin may have thinned before ∼13 ka, consistent with interior but without substantial marginal retreat [ABSTRACT FROM AUTHOR]

The impact of the Arctic stratospheric polar vortex on persistent weather regimes over North America is so far underexplored. Here we show the relationship between four wintertime North American weather regimes and the stratospheric vortex strength using reanalysis data. We find that the strength of the vortex significantly affects the behavior of the regimes. While a regime associated with Greenland blocking is strongly favored following weak vortex events, it is not the primary regime associated with a widespread, elevated risk of extreme cold in North America. Instead, we find that the regime most strongly associated with widespread extremely cold weather does not show a strong dependency on the strength of the lower stratospheric zonal mean zonal winds. We also suggest that stratospheric vortex morphology may be particularly important for cold air outbreaks during this regime. Plain Language Summary: During winter, the strength of the winds 10–50 km above the Arctic can affect the weather patterns at the surface. Generally, this influence is strongest over the North Atlantic and Europe. However, we show that the strength of stratospheric winds has a significant impact on weather patterns across North America. Our results indicate that knowledge of the stratospheric winds can provide a greater understanding of the evolution of likely weather in this region on longer time periods, including both severely cold weather (and its associated impacts on energy consumption, transport, and human health) and an unusual absence of severe cold. Key Points: The behavior of three of four regimes over North America is significantly linked to the strength of the lower stratospheric polar vortexA regime associated with Greenland blocking shows the strongest relationship with the stratospheric polar vortex strengthThe regime most strongly associated with widespread severe North American cold does not show a dependency on stratospheric vortex strength [ABSTRACT FROM AUTHOR]