Recent studies have revealed a marked increase in the occurrence and intensity of marine heatwaves in the waters surrounding India. Despite being relatively understudied in the tropical Indian Ocean, these phenomena have begun to draw serious attention due to their potential impacts on the marine environment and climate patterns. The Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) has predicted that under 1.5°C to 2°C global warming, the sea surface temperature over the Indian ocean will likely rise by 1 to 2 °C.
Key Findings From the Study
The study has elucidated several important findings. The Western Indian Ocean region, for instance, experienced the greatest rise in marine heatwaves with a rate of about 1.5 events per decade, followed by the north Bay of Bengal at a rate of 0.5 events per decade. The impact of these heatwaves has resulted in increased drying conditions over central India and an increase in rainfall over southern India. Between 1982 and 2018, there were 66 heatwave events in the Western Indian Ocean and 94 in the Bay of Bengal, all linked with modifications in monsoon winds by these heatwaves.
Marine Heatwaves Explained
Marine heatwaves refer to periods of exceptionally warm temperatures in the ocean. These events can cause extensive damage to marine ecosystems, including coral bleaching, seagrass destruction, kelp forest loss and negative repercussions for the fisheries sector. In fact, a post-heatwave study in 2020 discovered that 85% of the corals in the Gulf of Mannar near the Tamil Nadu coast had been bleached. The most common instigators of marine heatwaves are ocean currents, which accumulate areas of warm water, and air-sea heat flux, or warming through the ocean surface from the atmosphere. Weather factors such as winds and climate modes like El Niño can also influence the likelihood of heatwaves in particular regions.
Impacts of Marine Heatwaves
Marine heatwaves display far-reaching impacts. They can alter ecosystem structures, favoring certain species while suppressing others, and even triggering mass mortality events within marine invertebrates. Often they lead to changes in behaviour that puts wildlife at increased risk. Moreover, these heatwaves can shift the habitat ranges of certain marine species, leading to unexpected environmental and economic consequences. For instance, the spiny sea urchin off southeastern Australia is known to expand southward into Tasmania during heatwaves, causing damage to kelp forests.
Economic and Biodiversity Consequences of Marine Heatwaves
The economic implications of marine heatwaves are pronounced, negatively impacting fisheries and aquaculture industries. The effect on biodiversity can be devastating, as demonstrated in 2016 when widespread marine heatwaves caused severe bleaching of the Great Barrier Reef. Further, marine heatwaves often co-exist with other stressors such as ocean acidification, deoxygenation, and overfishing, exacerbating habitat damage and heightening the risk of deoxygenation and acidification.
Moving Forward: A Coordinated Response to Marine Heatwaves
Given the escalating frequency, intensity, and geographic reach of marine heatwaves, it is crucial to enhance ocean observation systems and improve weather models to predict the challenges a warming world presents. Adequately responding to these heatwaves necessitates collective action from a diverse range of stakeholders, including policymakers, researchers, the private sector, conservationists, and civil society. Local management agencies must raise awareness among all stakeholders and establish forecasting systems for a coordinated response. It is also incumbent upon national and sub-national governments to design and implement protective measures for communities and strengthen regional ocean resilience.
