Risk Analysis of Near-Coastal Species of the U.S. Pacific Coast: Case Study Comparing Risks Associated with Two Future Climate Scenarios
Lee II, H., C. Folger, Pat Clinton, D. Reuesser, AND R. Graham. Risk Analysis of Near-Coastal Species of the U.S. Pacific Coast: Case Study Comparing Risks Associated with Two Future Climate Scenarios. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-17/351, 2017.
To evaluate climate change risks under different emission scenarios, we developed a risk assessment framework to predict relative climate change risks for near-coastal species (0-200 m depth) at the scale of marine ecoregions. Using the online risk assessment tool (CBRAT, http://www.cbrat.org/), we compared risks under two climate scenarios: RCP 8.5 an unregulated, “business as usual” scenario and RCP 4.5 an intermediate scenario with reduced emissions of greenhouse gases. Risks were compared for all true crabs, king crabs, rockfish, and bivalves that occur in the ten ecoregions spanning Southern California through the Beaufort Sea. At the coastal scale summarizing across all ten ecoregions, the model predicted substantial decreases in number of ecoregions with species at high risk under RCP 4.5 compared to RCP 8.5. However, there was no consistent geographical pattern in risk reductions at the ecoregion scale. Across the four taxa, the model predicted no reduction in risk in some ecoregions with RCP 4.5 while substantial declines were predicted in others. A different type of climate impact is the colonization of northern ecoregions by southern species as the oceans warm. As with the risks, the model predicted no consistent geographical pattern in the reduction in the number of northern colonists per ecoregion. However, when summed over the ten ecoregions, the total number of potential colonists was predicted to be moderately to substantially reduced under the RCP 4.5 scenario, depending upon the taxon. Based on the reductions in predicted species at risk and number of northern colonists, we conclude that achieving the RCP 4.5 scenario would substantially reduce ecological risks to near-coastal species along the North American Pacific Coast. However, the variation among taxa and lack of simple geographical patterns in the extent of risks or in risk reductions with RCP 4.5 suggests that no single climate adaptation strategy is likely to be effective for all species or locations. This report contributes to ACE-CIVA 2.1.
Fundamental questions for climate change policy and adaptation strategies are to what extent does ecological risk change under different climate scenarios and how do any changes in risk vary among taxa and geographically. To evaluate these questions, we developed a rule-based framework to predict relative risks to temperature increases, ocean acidification, and sea level rise for near-coastal species (0-200 m depth) at regional scales. The framework is implemented in the ecoinformatics website Coastal Biodiversity Risk Analysis Tool (CBRAT, http://www.cbrat.org/). In our first case study, we compared the risks associated with Representative Concentration Pathway (RCP) 4.5 and 8.5. RCP 8.5 represents an unregulated, “business as usual” scenario while RCP 4.5 represents an intermediate scenario. Risk were evaluated for all the true crabs, king crabs, rockfish, and bivalves (total 694 species) occurring in the ten coastal ecoregions from Southern California to the Beaufort Sea. At the coastal scale summed across all ten ecoregions, the RCP 4.5 scenario showed substantial decreases in the percent of ecoregions with species at high risk compared to RCP 8.5. The reduction in high risks ranged from a 32% decrease for king crabs to a 93% decrease for bivalves. Concurrently, there was an increase in the number of ecoregions with species at moderate risk with the king crabs, rockfish, and bivalves. This pattern indicates that under the RCP 4.5 scenario, risks were reduced from high to moderate for many species. However, there was no consistent geographical pattern in risk reductions at the ecoregion scale. Across the four taxa, the model predicted no reduction in risk in some of the ten ecoregions with RCP 4.5 while substantial declines were predicted in others. However, for each taxon there was at least one ecoregion with a substantial (≥25%) reduction in the percent of specie at moderate or high risk. In three of the taxa, more than half of the occupied ecoregions showed a reduction in the percent of species at risk to climate change. Another effect of climate change is the potential for southern species to colonize currently unoccupied northern ecoregions as temperatures warm. This was evaluated by assessing the thermal suitability of currently unoccupied northern ecoregions for southern species. As with the risks, there was considerable geographic variation in the reduction of potential colonists per ecoregion under RCP 4.5. However, when evaluated at a coastal scale, there substantial decreases in the number of potential colonists were predicted in each of the four taxa under RCP 4.5. Generating simple conclusions regarding risk reduction with the RCP 4.5 scenario is complicated by the multiple ways that risk reductions can be quantified and the lack of consistent taxonomic and geographical patterns. Nonetheless, overall, we conclude that the RCP 4.5 scenario would substantially reduce ecological risks to true crabs, king crabs, rockfish, and bivalves along the North American Pacific Coast.