Heatwaves

Science  Socioeconomic impacts of marine heatwaves: Global issues and opportunities

BACKGROUND

Anthropogenic climate change is altering the structure and functioning of ecosystems globally. The upper layers of the oceans have absorbed >90% of the excess heat arising from human activities and, as a result, surface waters have warmed at an average rate of 0.15°C per decade over the past 40 years, with global ocean heat content currently at a record high. Many marine species have shifted their distributions in response to this ubiquitous warming, causing community reconfigurations and changes to entire ecosystems. In addition to gradual warming, the frequency and severity of short-term oceanic warming events, marine heatwaves (MHWs), has increased substantially, largely as a consequence of rising anthropogenic carbon emissions and ocean warming. The global annual number of MHW days has risen by 54% over the past century, with eight of the 10 most extreme MHWs ever recorded occurring after 2010. MHWs are forceful agents of disturbance with wide-ranging impacts on marine ecosystems, including driving species range shifts and mass mortalities and altering foodwebs and species interactions. Regional case studies have shown that ecological responses to MHWs can have socioeconomic implications such as loss of fisheries income, erosion of essential ecosystem services, mass mortalities of iconic species, and conflict. Although our understanding of the physical drivers and biological impacts from MHWs are becoming increasingly robust and predictive, only a few studies have examined their consequences for human-ocean interactions, a crucial step in understanding the associated costs and risks and in developing potential adaptation and mitigation measures.

ADVANCES

Using a large number of case studies, we provide a global perspective on the impacts of MHWs on the provision of ecosystem services and examine the socioeconomic implications. We show that these discrete warming events are altering ecosystem functioning with present-day ramifications for human-ocean interactions. Ecological impacts commonly include harmful algal blooms, species range shifts, mass mortality events, and ecosystem reconfiguration lasting from weeks to years or longer. Such ecological impacts affect humans by changing provisioning, habitat, regulating, and cultural ecosystem services. Clear socioeconomic consequences have been linked to at least 34 MHWs occurring across a wide range of ecosystems in all major ocean basins globally. Impacts on provisioning services relating to fisheries and habitat services relating to loss of foundation species (e.g., corals, kelps, and seagrasses) have been particularly prevalent. Impacts on cultural services relating to mass mortality of charismatic (e.g., sea lions, sea birds, and corals) and spiritual (e.g., certain kelp) species, and on regulating services relating to carbon sequestration and altered nutrient cycling were also common. Biological responses to extreme warming events can, however, also increase human-ocean interactions and offer short-term socioeconomic opportunities through, for example, increased tourism or fisheries prospects. Economic losses of single MHW events to date exceed US$800 million in direct losses and in excess of US$3.1 billion per annum in indirect losses for multiple consecutive years. The true costs are, however, likely to be much greater because many socioeconomic effects likely remain unknown and underreported, particularly in lower-income countries.

OUTLOOK

The likelihood and intensity of MHWs have increased substantially in recent decades, largely due to broad-scale warming attributed to anthropogenic climate change, and are projected to intensify in coming decades. Concurrently, reported ecological impacts, changes in ecosystem services, and economic losses have also increased markedly. We discuss potential adaptation and mitigation measures to reduce risks and consequences for human-ocean interactions and examine knowledge gaps in our current understanding of MHW impacts, for example, in relation to the likely exacerbating effects of other anthropogenic stressors. Globally, marine ecosystems are threatened by a diverse range of anthropogenic stressors, and policy, management, and conservation measures must prioritize approaches to alleviating them to ensure continued provision of ecosystem services. We demonstrate the far-reaching impacts of MHWs on present-day human-ocean interactions and highlight the urgent need to develop a coherent understanding of the linked social-ecological impacts of MHWs and robust approaches to mitigation and adaptation.

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