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About The Marine Heat Waves


July is expected to be the warmest month ever recorded on Earth, following the hottest June on record. Both land and sea surface temperatures have risen significantly, with ocean temperatures staying at record highs since 2016, leading to the occurrence of marine heat waves worldwide.


GS I: Geography

Dimensions of the Article:

  1. Marine Heat Waves (MHWs)
  2. Impact of Marine Heat Waves (MHWs)
  3. Impact of Global Warming on Marine Heat Waves and Oceans

Marine Heat Waves (MHWs)

  • A marine heat wave is an extreme weather event characterized by a significant increase in sea surface temperature in a specific region of the ocean.
  • It is defined as when the surface temperature rises 3 to 4 degrees Celsius above the average temperature for at least five consecutive days.
  • MHWs can persist for weeks, months, or even years.
  • Currently, MHWs have affected several regions, including the north-east Pacific, the southern hemisphere in the southern Indian Ocean and the Pacific, the north-east Atlantic, tropical North Atlantic, and the Mediterranean.

Impact of Marine Heat Waves (MHWs)

On Weather Pattern:

  • MHWs can intensify storms like hurricanes and tropical cyclones due to higher ocean temperatures, leading to increased evaporation and heat transfer to the air.
  • As the world gets warmer, MHWs are expected to become more intense and prolonged.

On Ocean Life:

  • MHWs can cause coral bleaching and the death of marine species, altering migration patterns.
  • They can lead to fish kills and destruction of kelp forests, fundamentally changing ecosystems.
  • MHWs fuel the growth of invasive alien species, disrupting marine food webs.
  • Wildlife may be at increased risk, as seen in whale entanglements in fishing gear.

On Humans:

  • Storms traveling over warm oceans gather more water vapor and heat, resulting in more powerful winds, heavy rainfall, and flooding when they reach land, causing heightened devastation for humans.
  • MHWs have significant socio-economic impacts on coastal communities, affecting fisheries and livelihoods.

Impact of Global Warming on Marine Heat Waves and Oceans:

  • Increased Frequency, Duration, and Intensity: Rising global temperatures have led to longer-lasting, more frequent, and intense marine heat waves (MHWs) in recent decades.
  • Ocean’s Role in Heat Absorption: The oceans have absorbed about 90% of the additional heat resulting from greenhouse gas emissions caused by human activities like burning fossil fuels and deforestation.
  • Sea Surface Temperature Rise: The global mean sea surface temperature has risen by nearly 0.9 degrees Celsius since 1850 due to this heat absorption by the oceans.
  • Correlation with Air Temperature: As global air temperatures increase, ocean temperatures also rise, contributing to the occurrence of more MHWs.
  • Impact of El Nino: The current El Nino weather pattern, characterized by abnormal warming of equatorial Pacific Ocean waters, is likely to exacerbate extreme heat events and break temperature records in various regions.

-Source: Indian Express

December 2023