New Delhi, Sept. 13 -- In the last two articles, we discussed the various types of ocean currents and their role in regulating heat and salinity across and within the oceans. In the third part, we will discuss the importance of the oceans as giant heat sinks and how they will play an important role in the long term, till the end of this century and beyond.
The Rising Emissions, Heating and the Oceans
We have seen in this series that carbon emissions continue unabated, and with the ongoing Iran war, it is likely that fossil fuel mining and burning by countries like India, China, Australia and Indonesia will only increase. The link between rising emissions and increasing temperatures across the Earth has been scientifically established. Climate models suggest that if countries continue with their current policies, temperatures are likely to rise by 2.8-3.2degC, while even if carbon dioxide reduction pledges are met, they could rise by 2.5-2.8degC. Further, carbon dioxide in the atmosphere is already at 430 ppm, and any further rise will have direct implications for ocean warming and its ability to absorb future heat.
Oceans as Giant Sinks
Rising emissions and global temperatures have contributed to the shrinking of Arctic and Antarctic ice sheets and glaciers. More specifically, the Greenland ice sheet has been melting at an accelerating rate of about 260-270 gigatons (Gt) per year on average since 2002, going up to 600 Gt in the warm years of 2012-19. This translates to about a 0.7 mm annual rise in sea levels. It is estimated that the current carbon dioxide concentration in the atmosphere has already locked in a future sea-level rise of 27 cm. Other estimates suggest that melting of the Greenland ice sheet will raise sea levels by 10-16 cm by the end of the century. The locked-in 27 cm rise will cause serious inundation and infrastructure damage in the Indian and Pacific Oceans. In the Indian Ocean, India and its coastal cities will be badly hit, including Mumbai, Chennai and Visakhapatnam, as well as West Bengal and the Sundarbans. Bangladesh, Vietnam and Indonesia will also be impacted. In the Pacific, the East Coast of the USA, including New York and Miami, as well as New Orleans and the Mississippi Delta, will be impacted. Small Pacific islands such as Tuvalu, Vanuatu, Kiribati, Fiji and the Solomon Islands face severe threats. European cities such as Venice, London and Rotterdam will need stronger sea defences. Sea-level rise will be compounded by storm surges, saltwater intrusion and infrastructure damage.
Let us look at Antarctica now. Incidents of calving from large glaciers have increased since 2015 because of warmer ocean waters. In particular, the breaking away of a 225-square-mile chunk of the Pine Island Glacier in 2015 indicated that warmer ocean water was seeping beneath the glacier and creating rifts, leading to more frequent calving. Similarly, the neighbouring Thwaites Glacier is losing ice at 50 Gt per year, accounting for 4% of global sea-level rise. Thwaites is even more critical, not only because of its size-it is roughly the size of Great Britain-but also because of its 'cork' effect. The glacier acts as a massive dam, holding back large ice masses of West Antarctica. Thwaites alone has the potential to raise sea levels by 65 cm, or about two feet. If the Thwaites Glacier collapses, it could also destabilise neighbouring glaciers, potentially contributing to a massive sea-level rise of 3 metres. This criticality gives Thwaites the name 'Doomsday Glacier'.
Then there is the Larsen Ice Shelf in Antarctica, which has been shedding large chunks of ice, with the massive A-68 iceberg breaking off from Larsen C in 2017. Larsen A and Larsen B had earlier collapsed in 1995 and 2002. A-68 weighed around one trillion tons and its separation reduced the area of Larsen C by 12%. Particularly worrying is the role of warmer ocean currents and 'atmospheric rivers'-streams of warm, moist air that contribute to surface melting, ultimately allowing glaciers to flow faster into the oceans and raise sea levels.
Conclusion
Oceans and ocean currents are critical to the way climate change will impact us. With warmer ocean waters chipping away at ice shelves and glaciers, sea-level rise is inevitable. The melting of the Greenland ice sheet alone has locked in a substantial future sea-level rise. In the longer term, the melting of Antarctic glaciers is an even greater cause for concern. It seems that shutting down fossil fuels immediately may not be enough: other mitigation and adaptation measures, along with ramped-up R&D, which we have discussed in this series, are a mus
Published by HT Digital Content Services with permission from Millennium Post.