Potential for Regional Resilience to Ocean Warming and Acidification Extremes: Projected Vulnerability Under Contrasting Pathways and Thresholds.

We analyze the frequency and amplitude of projected warming and ocean acidification extremes under high CO2 and strongly mitigating scenarios. We find interpretational differences in projections arising from methodological choices associated with specification of stressor thresholds. Use of absolute versus distribution-based thresholds, and, in the distribution-based case, the inclusion or exclusion of seasonal variability, can lead to very different regional patterns in projected stress. The choice of fixed versus adaptive baseline, for example, determines whether future stress frequency in the low-CO2 scenario most closely resembles that in the high-emissions scenario or historical period. We find that mitigation through emissions reductions, in combination with representation of rates of adaptation that are realistic for some marine organisms, has the potential to dampen end of century threshold exceedance to frequencies of occurrence closer to the recent historical period than to the high-emissions scenario.