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Coupled Climate Stressors along the West Coast of North America: Drought, Marine Heat Waves, HABs, and Hypoxia

Project Summary:
Climate change is increasing variability in earth systems, resulting in more extreme weather and
ecosystem events. Currently, an unprecedented multi-year marine heat wave, severe drought,
and short-term bouts of severe hypoxia and harmful algal blooms (HABs) in the coastal marine
environment are gripping the western United States, causing a variety of biological impacts and
socio-economic hardships. While each of these extreme events might be a chance occurrence on
its own under natural climate forcing, their current spatiotemporal coincidence may indicate that
the recent events are attributable to anthropogenic climate change. The simultaneity of the
stressors in these coupled terrestrial and marine ecosystems may stimulate combined ecological
catastrophes in western states that are unlike those experienced previously. In this project, we
hypothesize that the synchrony of fires and drought (and hence, poor air quality) in the terrestrial
realm are mechanistically coupled to episodes of hypoxia, harmful algal blooms, heat waves, and
acidification in the coastal marine environment through large-scale atmospheric forcing.

To test this hypothesis, we propose to use the ensemble of Earth System Model (ESM) output
produced as part of the CMIP6 effort and explore three metrics of change in ecosystem
conditions: 1) change in mean state; 2) change in the interannual variability of extremes (both
frequency and intensity); and 3) shifts in the seasonal cycle. Each of these characteristics can
have important (and distinct) implications for the marine and terrestrial events considered here.
Anthropogenic changes in the frequency and intensity of extreme events and anomalies in the
seasonal cycle will be assessed using fraction of attributable risk (FAR) analyses. Key
ecosystem properties relevant to the marine biogeochemical and terrestrial events of focus will
be selected. Mean states, seasonalities, and variabilities will be assessed under forcing from both
historical simulations (long control runs and historical forcing of CMIP6 Earth System models)
and simulations associated with future shared socioeconomic pathways; and FAR analyses will
be used to investigate the changes in likelihood of such simultaneous events under future climate
scenarios. Improved understanding of the frequency of these events under future climate
forcing—particularly the chances that they will occur simultaneously in marine, freshwater, and
terrestrial systems—can inform efforts to adapt and prepare for such catastrophes.

Relevance to the Competition and to NOAA’s Long-term Climate Goals:
The proposed project is directly applicable to the research priorities of the CPO and Competition
6 as it will evaluate changes in the likelihood of extreme events that impact the sustainability of
marine and terrestrial ecosystems and the resiliency of coastal communities—challenges that are
prominent in the strategy of the CPO and its focus on climate intelligence and climate resilience. We
will develop an integrated, process-level understanding of the dynamics of specific climate-
related catastrophes in CMIP6 Earth System models. Such effort will also inform decision makers 
and facilitate the development of indices that can be leveraged by groups across NOAA
and among partner agencies.

Climate Risk Areas: Water Resources, Marine Ecosystems

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