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

## TL;DR

The study explores how different methods of measuring ocean warming and acidification extremes affect predictions of marine stress under various CO2 emission scenarios.

## Contribution

The novelty lies in showing how methodological choices in defining stressor thresholds significantly influence regional vulnerability projections.

## Key findings

- Mitigation through emissions reductions can reduce end-of-century stress frequencies to levels closer to historical norms.
- The choice of fixed or adaptive baselines affects whether low-CO2 scenarios resemble historical or high-emissions stress patterns.
- Incorporating realistic adaptation rates in models can dampen projected stressor exceedance frequencies.

## Abstract

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.

We analyze the frequency and amplitude of projected warming and ocean acidification extremes under a high and a lower, strongly mitigating, CO2 scenario and find interpretational differences arising from choices associated with the specification of stressor thresholds. The choice of fixed versus adaptive baseline determines whether future stress frequency in the low‐CO2 scenario most closely resembles the high‐emissions scenario or the historical period. Mitigation through emissions reductions, combined with the representation of rates of adaptation realistic for some marine organisms, has the potential to dampen end‐of‐century threshold exceedance to frequencies closer to the recent historical period than to the high‐emissions scenario.