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

Context- The average global sea surface temperature (SST) in February 2024 reached a record high of 21.06°C, according to the Copernicus Climate Change Service (C3S). This is the highest temperature recorded in a dataset dating back to 1979. The previous record was 20.98°C in August 2023. Since March 2023, the average daily SST has been exceptionally high. The data for 2024 so far indicates temperatures significantly higher than any previous year, including 2023.

Why are the oceans getting warmer?

  • Since the 19th Century Industrial Revolution, human activities like burning fossil fuels have released significant levels of greenhouse gases (GHGs) such as carbon dioxide, methane, ozone, and nitrous oxide into the atmosphere.
  • These GHGs trap heat, contributing to global warming and causing the average global temperature to rise at least 1.2°C above pre-industrial times.
  • Almost 90% of the extra heat trapped by GHGs has been absorbed by the oceans, leading to a steady increase in their temperature over the decades. Biological oceanographer Francisco Chavez stated that the oceans have mitigated climate impacts by absorbing and storing heat not just at the surface, but also at depths.
  • In addition to global warming, other factors have contributed to the rise in ocean temperatures. For example, El Niño, a weather pattern characterized by abnormal warming of surface waters in the equatorial Pacific Ocean, has contributed to ocean warming and rising global surface temperatures.
  • The global daily average sea surface temperature (SST) began to rise significantly before El Niño fully developed and remains unusually high even as the weather pattern is waning.
  • Recently, there has been less dust blowing off the Sahara Desert due to weaker-than-average winds. This dust typically forms a “giant umbrella” that shades the Atlantic water and reduces ocean temperatures.
  • However, with the umbrella now partially folded, more sunlight is reaching the ocean, further increasing its temperature.

Why are rising sea surface temperatures a cause of worry?

  • Rising ocean temperatures can lead to irreversible impacts on marine ecosystems. Warmer oceans increase ocean stratification, which is the layering of water by density.
  • This makes it harder for different water layers to mix, reducing the ocean’s ability to absorb carbon dioxide and properly mix oxygen with cooler waters below, threatening marine life.
  • The inability of nutrients to travel up to the ocean’s surface could endanger phytoplankton populations, the base of many marine food webs. A decline in phytoplankton could lead to a collapse of marine ecosystems.
  • Warmer oceans also cause marine heat waves (MHWs), where the sea surface temperature of a region rises 3 or 4°C above average for at least five days. MHWs have doubled in frequency and become longer and more intense from 1982 to 2016.
  • They contribute to coral bleaching, reducing coral reproductivity and making them more disease-prone, and affect the migration patterns of aquatic animals.
  • Higher ocean temperatures could also lead to more frequent and intense storms like hurricanes and cyclones. Warmer temperatures increase evaporation rates and heat transfer from oceans to air, intensifying storms as they gather more water vapor and heat.
  • This results in stronger winds, heavier rainfall, and more flooding when storms reach land, causing increased devastation for humans.
  • The only way to mitigate these consequences is to reduce greenhouse gas emissions. However, in 2023, the concentration of greenhouse gases reached the highest levels ever recorded in the atmosphere.

Conclusion- The escalating ocean temperatures, driven by human-induced greenhouse gas emissions, are causing profound and potentially irreversible impacts on marine ecosystems. The increased stratification of ocean waters is disrupting the absorption of carbon dioxide and oxygen, and the transportation of nutrients, threatening marine life and the stability of marine food webs. Marine heat waves, which have doubled in frequency and intensity, are causing widespread coral bleaching and altering the migration patterns of aquatic animals. Furthermore, the warmer oceans are intensifying storms, leading to more devastating hurricanes and cyclones.

Despite the urgent need to reduce greenhouse gas emissions to mitigate these impacts, the concentration of these gases reached record levels in 2023. The situation underscores the critical need for immediate and substantial global action to curb greenhouse gas emissions and combat climate change.

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