Marine Heat Waves

Context: At present, Marine Heat Waves are occurring in several oceans, including the northern two-thirds of the Pacific Ocean, the southern Indian Ocean, and some parts of the Atlantic Ocean, as well as the Mediterranean Sea.

What Are Marine Heat Waves (MHWs)?

• A MHW is an extreme weather event. It occurs when the surface temperature of a particular region of the sea rises to 3 or 4 degree Celsius above the average temperature for at least five days.
• MHWs can last for weeks, months or even years, according to the US government’s agency National Oceanic and Atmospheric Administration (NOAA).
• According to the International Union for Conservation of Nature (IUCN), MHWs have increased by 50% over the past decade and now last longer and are more severe.
• Projections suggest that by 2100 MHWs will occur as many as 50 times as often as in pre-industrial times, and increase 20-50 times in frequency and 10 times in intensity.

Factors Behind Marine Heat Waves (MHWs)

• Global Warming: A 2018 study, ‘Marine heatwaves under global warming’, published in the journal Nature, showed that with the soaring global temperatures, MHWs have become longer-lasting, more frequent and intense in the past few decades.
  • Research suggests that the oceans have absorbed 90 per cent of the additional heat caused by the release of greenhouse gases which has increased the global mean sea surface temperature by close to 0.9 degree Celsius since 1850.
• El Nino: El Nino further worsens MHWs by triggering more heating of the ocean surface.
  • El Nino is a weather pattern that refers to an abnormal warming of surface waters in the equatorial Pacific Ocean.

Impact of Marine Heat Waves on Ocean Life

• Biodiversity Loss: Marine heatwaves can disrupt marine ecosystems, leading to changes in the distribution and abundance of species.
  • For instance, MHWs along the Western Australian coast during the summer of 2010 and 2011 caused some “devastating” fish kills.
• Kelp Forest Degradation: A different study revealed that the same MHWs destroyed kelp forests and fundamentally altered the ecosystem of the coast.
  • Kelps usually grow in cooler waters, providing habitat and food for many marine animals.
• Coral Bleaching: Corals are very sensitive to the temperature of the water in which they live. When water gets too warm, they expel the algae known as zooxanthellae, living in their tissues, causing them to turn entirely white. This is called coral bleaching.
  • For example, when high ocean temperatures in the tropical Atlantic and Caribbean in 2005 led to a massive coral bleaching event.
  • Coral bleaching has severe consequences as it reduces the reproductivity of corals and makes them more vulnerable to fatal diseases.
  • Also, thousands of marine animals depend on coral reefs for survival and damage to corals could, in turn, threaten their existence.
• Invasive Species: MHWs also fuel the growth of invasive alien species, which can be destructive to marine food webs.
• Behavioural Changes in Species: MHWs force species to change their behaviour in a way that puts wildlife at increased risk of harm.
  • MHWs have been linked to whale entanglements in fishing gear, according to a report by the IUCN.
• Impact on Ocean Chemistry: MHWs are not the only threat to marine ecosystems; often they occur alongside other stressors such as ocean acidification, deoxygenation, and overfishing.
  • In such cases, MHWs not only further damage habitats, but also increase the risk of deoxygenation and acidification.
  • Ocean acidification refers to a reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere.
  • Deoxygenation is the overall decline in the oxygen content of oceanic and coastal waters. As, warm water holds less oxygen, MHWs can trigger deoxygenation.

Impacts of Marine Heat Waves on Humans

• Extreme Weather Events: Higher water temperatures associated with MHWs can cause extreme weather events such as tropical storms and hurricanes, and disrupt the water cycle; making floods, droughts and wildfires on land more likely.
• Sea level rise: As the oceans warm, they expand and cause sea levels to rise, which can flood coastal communities and damage infrastructure.
• Socio-economic Impacts: MHWs have other profound socio-economic impacts for coastal communities.
  • Impact on Aquaculture: Several fish species relocate in response to changing ocean temperatures leading to reduced fish catches and affecting coastal livelihoods.
  • A study found that MHWs reduced the productivity of economically important species including lobster and snow crab in the northwest Atlantic and scallops off Western Australia.
  • Impact on Tourism: MHWs can also harm regional tourism, particularly in areas that rely on marine-based attractions and activities.
  • Impact on Human Health: As temperatures rise, certain types of harmful microorganisms can multiply, which can contaminate seafood and make it unsafe to eat.
• Ocean warming is a positive feedback loop for global warming. As the oceans warm, they release more heat and moisture into the atmosphere, leading to changes in global precipitation patterns as well as temperatures.

Way Forward

• Mitigation: Reducing greenhouse gas emissions is crucial to slow down global warming and the frequency of MHWs.
  • Governments and industries should invest in renewable energy sources, promote energy efficiency, and adopt sustainable practices to mitigate climate change.
• Adaption: National and sub-national governments should design and implement measures to protect communities and build regional ocean resilience.
  • Examples of such measures include creating and protecting marine protected areas to act as refuges for species of coral, kelp and seagrass; and enforcing catch management or fishing restrictions to help limit economic losses linked to MHWs.
• Nature Based Solutions: Governments must invest in nature-based solutions alongside ambitiously reducing fossil fuel-based emissions to achieve the goals agreed to under the Paris Agreement.
  • Nature-based solutions refer to a suite of actions or policies that harness the power of nature to address some of our most pressing societal challenges, such as threats to water security, rising risk of disasters, or climate change.
• Research and Monitoring: Invest in research and monitoring programs to better understand MHWs, their impacts, and their future projections.
• International Collaboration: Foster international collaboration and networks, such as the Marine Heatwave International Group, to share knowledge, data, and best practices in addressing MHWs on a global scale.

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