Warming up to climate change: Why do global sea surface temperatures matter?

GS Paper III

News Excerpt: 

In February 2024, the global sea surface temperature (SST) reached a historic high of 21.06 degrees Celsius, as reported by the Copernicus Climate Change Service (C3S) on March 5, 2024.

  • This marks the highest recorded SST since data collection began in 1979, surpassing the previous record of 20.98 degrees Celsius was set in August 2023.

More About the News: 

  • Since March 2023, daily average SST has consistently exceeded previous years' temperatures, as depicted in the graph below. The orange line represents 2023's temperatures, while the grey lines track temperatures from earlier years. 
  • The solid black line illustrates the SST for 2024, which notably surpasses all previous years, including 2023.

Why Oceans Are Getting Warmer: 

  • Human Factors: The oceans are experiencing warming primarily due to human activities, particularly since the onset of the Industrial Revolution in the 19th century. This period has seen significant emissions of greenhouse gases (GHGs) such as carbon dioxide, methane, ozone, and nitrous oxide, which trap heat in the atmosphere, leading to global warming. As a result, the global average temperature has risen by approximately 1.2 degrees Celsius above pre-industrial levels.
  • GHG Emission: A substantial portion of the excess heat generated by GHGs has been absorbed by the oceans, causing them to gradually warm over time. a biological oceanographer at the Monterey Bay Aquarium Research Institute in California, highlighted the critical role of oceans in mitigating climate impacts, as they absorb and redistribute heat, thereby potentially alleviating the severity of climate change effects.
  • Climatic factors: Additionally, factors like El Niño, characterized by abnormal warming of surface waters in the equatorial Pacific Ocean, have contributed to rising ocean temperatures and global surface temperatures.
    •  However, it's noteworthy that the global daily average sea surface temperature began to rise well before the full onset of El Niño and has remained unusually high even as this weather pattern diminishes.
  • Atmosphere Dynamics: Furthermore, changes in atmospheric dynamics, such as weaker-than-average winds leading to reduced dust blowing off the Sahara Desert, have also influenced ocean temperatures. Typically, this dust forms a protective barrier that shades Atlantic waters, thus lowering ocean temperatures
    • However, recent conditions have resulted in less dust cover, allowing more sunlight to penetrate the ocean surface and contribute to its warming.

Why are rising sea surface temperatures a cause of worry:

  • Impact on Marine Ecosystem: Rising sea surface temperatures pose significant concerns due to their impact on marine ecosystems
    • One consequence is increased ocean stratification, where layers of water with varying temperatures, salinity, and nutrient levels become less likely to mix. 
    • This impedes the ocean's ability to absorb carbon dioxide from the atmosphere and distribute oxygen effectively, endangering marine life.
  • Nutrient Movement: The reduced mixing also restricts nutrient movement from deeper waters to the surface, potentially leading to declines in phytoplankton populations
    • Phytoplankton form the foundation of many marine food webs, and a decrease in their numbers could trigger ecosystem collapse, affecting species throughout the marine environment.


  • It is a  single-celled plant that thrives on the ocean surface and is the base of several marine food webs. 
  • Phytoplankton are eaten by zooplankton, which are consumed by other marine animals such as crabs, fish, and sea stars.
  • Marine Heatwaves: Moreover, warmer oceans contribute to the occurrence of marine heatwaves (MHWs), characterized by prolonged periods of exceptionally high sea surface temperatures
    • These events have doubled in frequency and intensity between 1982 and 2016, according to the Intergovernmental Panel on Climate Change (IPCC). 
    • MHWs have devastating effects on marine life, including coral bleaching, which weakens coral reefs and disrupts aquatic ecosystems.
  • Rise in Storms: Additionally, higher ocean temperatures are linked to the intensification of storms such as hurricanes and cyclones. 
    • This is due to increased evaporation rates and the transfer of heat energy from the ocean to the atmosphere, fueling storm development
    • Consequently, these storms become more powerful, resulting in stronger winds, heavier rainfall, and heightened flooding upon landfall, posing increased risks to human populations.


Addressing these concerns requires substantial reductions in greenhouse gas emissions, yet current emission levels continue to rise. In 2023, greenhouse gas concentrations reached record highs, underscoring the urgent need for global action to mitigate climate change and its adverse effects on marine ecosystems and human communities.

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