Context

• • The European Union’s Copernicus Climate Change Service (C3S) revealed that the global sea surface temperatures — the temperature of the ocean’s surface layer — were highest on record in February 2024. 

• C3S is one of six thematic information services provided by the Copernicus Earth Observation Programme launched by the European Union in 2014. 

• The average global sea surface temperature soared to an unprecedented high of 21.06 degrees Celsius. 
• This figure eclipses the previous record set in August 2023 by a slight yet significant margin, a continuous trend of escalating ocean temperatures that have been meticulously recorded since 1979.

Why are the oceans getting warmer?

• 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. 
• As a result, the average global temperature has risen at least 1.2 degree Celsius above pre-industrial times.
• Notably, almost 90 per cent of the extra heat trapped by GHGs has been absorbed by the oceans, making them steadily warmer over the decades. 
• Apart from global warming, there are other factors which have led to a spike in ocean temperatures. For instance, 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. 

Why are rising sea surface temperatures a cause of worry?

• Higher ocean temperatures can have irreversible consequences for marine ecosystems. For instance, 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.
• Nutrients are also 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. 
• 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 heat waves have doubled in frequency and have become longer and more intense.
• MHWs are devastating for marine ecosystems as they contribute to coral bleaching, which reduces the reproductivity of corals and makes them more vulnerable to life-threatening diseases. They also impact the migration pattern of aquatic animals.
• Higher ocean temperatures may also result in more frequent and more intense storms like hurricanes and cyclones. Warmer temperatures lead to a higher rate of evaporation as well as the transfer of heat from the oceans to the air. 
• 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.