Enhanced Atlantic Sea Level Rise Under High Carbon Emission Rates

An important component of historical sea level rise is the thermal expansion of the world ocean in response to a warming climate. Recent observational studies show that the Atlantic and Southern Oceans are warming at a faster rate than the Pacific and may be linked to the recent "hiatus decade" in climate warming. We demonstrate that climate warming can force basin-scale asymmetries in ocean heat uptake and sea level rise. Using a state-of-the-art coupled climate carbon cycle model forced with seven different carbon emission rates (2, 3, 5, 10, 15, 20, and 25 GtC/yr), we find that higher carbon emission rates (5 GtC/yr, present day rate is about 10GtC/yr) lead to enhanced sea level rise in the Atlantic relative to the Pacific on timescales of several centuries. Low emission rates (2 and 3 GtC/yr) produce more uniform sea level rise during the first several centuries before Pacific sea level rise overtakes the Atlantic on millennial timescales. This basin scale asymmetry is related to differing ocean ideal ages in the basins and a reduction in ventilation through overturning processes that is dependent on the carbon emission rate. This difference in relative vulnerability, Atlantic versus the Pacific, has implications for prioritization of coastal defense activities. We find that largest sea level rise for a given level of cumulative emissions occurs under low emission rates, larger inter-basin differences in sea level rise occur under higher emission rates. These findings confirm that sea level rise is not proportional to cumulative emissions. However, we demonstrate that cumulative emissions may be a predictor of the upper ocean (0-700m) temperature differences between the Atlantic and Pacific basins. Applying these metrics to historical observations -- namely the inter-basin differences in sea level rise -- could be an additional emergent constraint on model responses to increasing greenhouse gases.