Rising Global Sea Surface Temperature

General Studies Paper -3

Context: The average global sea surface temperature (SST) for February 2024 stood at 21.06 degree Celsius, the highest ever in a dataset that goes back to 1979.

• Sea surface temperature is the temperature of the water at the ocean surface.

Reasons for Rising SST

• Human Activities:Since the Industrial Revolution kicked off in the 19th Century, human activities such as burning fossil fuels have released high levels of greenhouse gases (GHGs) in the atmosphere.
• Carbon dioxide, methane, ozone, and nitrous oxide are some of the notable GHGs, which trap heat in the atmosphere and contribute to global warming.
• As a result, the average global temperature has risen at least 2 degree Celsius above pre-industrial times.
• Absorption by Oceans:Almost 90 percent of the extra heat trapped by GHGs has been absorbed by the oceans, making them steadily warmer over the decades.
• El Niño: A weather pattern that refers to an abnormal warming of surface waters in the equatorial Pacific Ocean — has contributed to both ocean warming and rising global surface temperatures. 
• Weaker Winds:There is also less dust blowing off the Sahara Desert recently due to weaker-than-average winds. 
• Typically, the dust forms a “giant umbrella that shades” the Atlantic water and reduces ocean temperatures.
• But now, the umbrella has partially folded and more of the Sun is beating down on the ocean.

Impact of Rising SST

• Ocean Stratification:Warmer oceans lead to an increase in ocean stratification — the natural separation of an ocean’s water into horizontal layers by density, with warmer, lighter, less salty, and nutrient-poor water layering on top of heavier, colder, saltier, nutrient-rich water.
• Usually, ocean ecosystems, currents, wind, and tides mix these layers.
• The rise in temperatures, however, has made it harder for water layers to mix with each other. 
• Due to this, oceans are able to absorb less carbon dioxide from the atmosphere and the oxygen absorbed isn’t able to mix properly with cooler ocean waters below, threatening the survival of marine life.
• Threat to Phytoplanktons: Nutrients are not able to travel up to the surface of the oceans from below. This could threaten the population of phytoplankton — single-celled plants that thrive on the ocean surface and are the base of several marine food webs.
• Phytoplankton areeaten by zooplankton, which are consumed by other marine animals such as crabs, fish, and sea stars.
• Therefore, if the phytoplankton population plummets, there could be a collapse of marine ecosystems.
• Marine Heat Waves:Warmer oceans cause marine heat waves (MHWs), which occur 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. 
• Between 1982 and 2016,such heatwaves have doubled in frequency and have become longer and more intense, according to the UN’s Intergovernmental Panel on Climate Change (IPCC).
• MHWs are devastating for marine ecosystems as they contribute to coral bleaching, and also impact the migration pattern of aquatic animals.
• Increase in Intensity of Cyclones:Warmer temperatures lead to a higher rate of evaporation as well as the transfer of heat from the oceans to the air. 
• That’s why, when storms travel across hot oceans, they gather more water vapour and heat.
• This results in more powerful winds, heavier rainfall, and more flooding when storms reach the land — meaning heightened devastation for humans.

Conclusion

• In 2023, the concentration of GHG the highest levels ever recorded in the atmosphere.
• The only way to avoid or blunt the aforementioned consequences is to reduce GHG emissions.