How is global warming affecting oceans?
- There are two broad mechanisms at work.
- Heat trapped in the atmosphere due to rising sea levels makes water expand.
- Melting ice sheets begin to add water to the world’s oceans.
- NASA’s satellite data shows that the seas on average have risen 85 mm since 1993, adding about 3.5 mm annually.
What is peculiar about the Indian Ocean?
- The Indian Ocean has been rising rapidly, particularly since 200.
- It was specific to a smaller stretch called the North Indian Ocean, which consists of the Bay of Bengal, the Arabian Sea and a large part of the Indian Ocean until the 5 degree S latitude.
- North Indian Ocean sea levels actually dipped between 1993 and 2004, at about 0.3 mm per year, but after 2004, the rise was 6 mm annually.
- Such a fluctuating trend hasn’t been observed for the Pacific Ocean and the Atlantic Ocean.
Why did this happen?
- The North Indian Ocean is surrounded by land on all sides, except an outlet on the southern side.
- This influences the rate at which heat is absorbed and flushed out from within the system.
- Wind flows, which led to warm water welling up on the Indian Ocean surface, changed directions every decade and probably influenced sea level patterns.
What does this imply?
- This means a rise in average global temperature doesn’t mean a concurrent rise in sea levels everywhere.
- Every year in the last decade has broken temperature records that have held for over a century.
- But researchers believe that North Indian Ocean levels may see a fall over the next decade (like seen between 1993 and 2004).
What should be done?
- These points to a need for more research to understand the inherent variability of the Indian Ocean.
- This could help sharpen monsoon forecasts and predicting coastal erosion patterns.
- Better understanding of sea level undulations could also inform future reports by the Intergovernmental Panel on Climate Change.
Source: The Hindu
