The ocean covers almost three-quarters of the planet. It is divided into five basins: the Pacific, the Atlantic, the Indian, the Arctic and the Southern oceans. Climate and weather systems depend on the temperature patterns of the ocean and its interactions with the atmosphere. Changing temperatures and chemistry, overfishing and pollution have stressed its ecosystems for decades. The ocean stores more than nine-tenths of the heat trapped on Earth by greenhouse-gas emissions.

2018 was the warmest year on records for the oceans. The Fifth Assessment Report published by the Intergovernmental Panel on Climate Change (IPCC) in 2013 revealed that the ocean had absorbed more than 93% of the excess heat from greenhouse gas emissions since the 1970s. This is causing ocean temperatures to rise. As oceans get warmer, there are many ramifications:

• Rising sea levels:
  1. When water heats up, it takes up more space. That means as oceans warm, sea levels rise. The study says this effect alone could make sea levels rise 30cm (12 inches) by the end of the century.
  2. Many large cities around the world, much built on reclaimed land, that are not more than 30cm above sea level. Example: Mumbai, Sydney
  3. But on top of that, warming oceans are causing polar ice sheets to melt faster, which will make sea levels rise even more.
  4. The combination of melting ice and expanding water could cause sea levels to rise by up to a meter by 2100. Hundreds of millions of people could be forced to be climate refugees.
• Extreme weather gets more extreme:
  1. Warmer oceans make tropical storms more intense and longer lasting.
  2. Cyclones become worst by unusually warm ocean temperatures.
  3. For coastal areas already struggling with rising seas, those storms will bring even more flooding.
  4. Warming temperatures also mean changing rainfall patterns. Redistribution of water vapour in the atmosphere takes place. Higher temperatures lead to more evaporation, so parts of the earth will get wetter and parts will get drier.
• Ocean life under threat:
  1. Thermal expansion leads to de-oxygenation. Some areas of Japan, Taiwan and the Baltic Sea are seeing dramatic die-offs of fish because of low oxygen.
  2. Coral Bleaching: Coral reefs are especially sensitive to warmer seas. Between 2016 and 2017, half the corals at the Great Barrier Reef were killed by two ocean heat waves.
  3. Almost three-quarters of the world’s coral reefs were affected by those heat waves and experts say warmer oceans mean these sorts of die-offs will become much more common.
  4. Another problem for sea life is that increased flooding causes more nutrients to be washed into the sea. This leads to plankton blooms and ultimately causes some parts of the sea to be starved of oxygen, making it hard for fish to live there.
• Food security:
  1. Fish species respond to warmer oceans by migrating to cooler areas. But the waters in some parts of the world are getting too warm for any fish — and that could lead to food shortages in those areas.
  2. A 2012 report by the Food and Agriculture Organization of the United Nations estimates that marine and freshwater capture fisheries and aquaculture provide 4.3 billion people with about 15% of their animal protein.
  3. There is a severe food security risk in the tropics.
• Melting sea ice:
  1. Warmer seas are causing sea ice to melt. Sea ice floats on the ocean surface, so when it melts it doesn’t affect sea levels. But it means there’s less sea ice to reflect heat from the sun back into space, which means the planet gets warmer.
  2. It’s bad news for animals that depend on sea ice to survive — including polar bears. But it’s also a problem for some Arctic communities.
  3. The Inuit living in Canada, for example, is a culture based on sea ice. They get their food by hunting seals and polar bears from sea ice, or fishing from sea ice. When the sea ice is disappearing that’s not possible, so the whole culture is being lost.
• Newer threats:
  1. Increasing the prevalence of diseases.
  2. Mutations leading to more superbugs.

Way Forward:

• 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.
• 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.

Conclusion:

Thus, a global effort is imperative to reduce the effects of warmer oceans. Mitigation and Adaptation measures will help us more resilient against extreme weather events.