Context: The report by Copernicus Climate Change Service (C3S) indicates that average sea -surface temperature has reached a new high in February 2024. This unusual warming of oceans is gradually acquiring a usual color, thereby posing grave threat for ocean ecosystem and biodiversity in particular and the Earth in general.
Reasons for warming of oceans:
- Increasing absorption of greenhouse gases emissions: The average global temperature has risen by at least 1.2 degree Celsius above pre-industrial times on account of high levels of GHGs emissions. Consequently, oceans have absorbed around 90% of the extra heat trapped by the GHGs, thereby leading to the excess warming of oceans.
- Impact of El-Nino: This phenomenon results in temperature rise in eastern equatorial pacific ocean.
- Saharan impact on Atlantic: The blowing of dust from Sahara desert acted as a giant umbrella to shade the Atlantic water and reduces ocean temperatures. But now this dust umbrella has partially folded, resulting in the increased heating of the Atlantic ocean.
- Impact of Sulphate aerosols: Sulphate aerosols on account of SO2 emissions act like a cloud, preventing solar radiation from reaching the ocean surface. But the decline in SO2 emissions on account of decline in Sulphur in marine fuels has negated this favorable impact.
- Weakening of Ocean Current: Weakening of ocean currents has impacted the heat regulation in oceans.
Impact of Warming of oceans:
- Ocean Stratification: Warmer oceans lead to an increase in ocean stratification i.e. the natural separation of ocean 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.
- Impacting the Ocean biodiversity: Due to ocean stratification, nutrients are not able to travel up to the surface of the ocean and so there is no intermixing. This threatens the population of the phytoplankton that thrive on the ocean surface and are base of several marine food webs.
- Rising sea levels: Warming of oceans leads to thermal expansion of water and also melting of glaciers in the polar areas. This leads to coastal inundation of low lying areas and also saline intrusion in groundwater reservoirs.
- Rising frequency of Marine Heat Waves (MHWs): MHWs are the abrupt rise in the surface temperature of a particular region of the sea by around 3 to 4 degrees Celsius above the average temperature for at least five days. Ex: Between 1982 and 2016, MHWs have doubled in frequency and have become more intense (IPCC report).
- Coral bleaching: Excessive warming of oceans has led to the discharge of zooxanthellae algae by Corals, thereby bleaching them to white color. This coral bleaching reduces the productivity of corals and makes them more vulnerable to life-threatening diseases like white band disease and black band disease.
- Loss of marine life: MHW events have also contributed to the sudden and unexpected death of many fish and other aquatic animals over a short period of time.
- Impact on migration of marine species: Warming of oceans has impacted the migratory patterns like early migration of heat loving marine species northwards, shifting of mangroves such as in Atlantic northwards towards moderately warmer areas.
- Intensification of the cyclones: The excessive warming of oceans has contributed to higher rate of evaporation and in turn more latent heat of evaporation as fuel for intensifying the cyclonic wind.
Way Forward:
- WMO in its State of Global Climate report has highlighted that there is 66 percent chance that at least one of the years between 2023 and 2027 would cross the threshold of 1.5 degree Celsius (Paris target)
- In this regard, it is important to achieve the goals set out in programs like Mangroves for Future
- Limiting greenhouse gas emissions: There is an urgent need to achieve the mitigation targets set by the Paris Agreement on climate change and hold the increase in the global average temperature to well below 2°C above pre-industrial levels. This will help prevent the massive and irreversible impacts of growing temperatures on ocean ecosystems and their services.
- Protecting marine and coastal ecosystems: Well-managed protected areas can help conserve and protect ecologically and biologically significant marine habitats. This will regulate human activities in these habitats and prevent environmental degradation.
- Restoring marine and coastal ecosystems: Elements of ecosystems that have already experienced damage can be restored. This can include building artificial structures such as rock pools that act as surrogate habitats for organisms or boosting the resilience of species to warmer temperatures through assisted breeding techniques.
- Improving human adaptation: Governments can introduce policies to keep fisheries production within sustainable limits, for example by setting precautionary catch limits and eliminating subsidies to prevent overfishing. Coastal setback zones which prohibit all or certain types of development along the shoreline can minimise the damage from coastal flooding and erosion. New monitoring tools can be developed to forecast and control marine disease outbreaks.
- Strengthening scientific research: Governments can increase investments in scientific research to measure and monitor ocean warming and its effects. This will provide more precise data on the scale, nature and impacts of ocean warming, making it possible to design and implement adequate and appropriate mitigation and adaptation strategies.