India and China lead the list of countries likely to be most affected by a 4 degrees Celsius rise in temperature caused by carbon emissions, according to a report by Climate Central - a US based non-profit research organisation.

The rise in sea levels because of the climate change can lead to the submergence of land inhabited by 200 million people in the two countries alone, and 470 to 760 million people globally.

Global megacities in Asia, with the top ten populations, that may lose the most land to sea are Shanghai, Hong Kong, Calcutta, Mumbai, Dhaka, Jakarta, and Hanoi.

Limiting the rise in temperature to 2 degrees Celsius would, however, reduce the risk for 35 million people in India and 64 million in China. 

China and India, among other countries would receive major benefits in their coastal areas by cutting carbon emissions that would limit the rise in temperature to 2 degrees Celsius.

Cities in India – Calcutta, Mumbai and Cuttack - should restrict exposure to 24%, 27% and 7% of its population as opposed to 51%, 50% and 18% should the temperature rise to 4 degrees Celsius.

In China, Hong Kong, Tianjin and Shenzen can, similarly, restrict the repercussions to 31%, 12% and 9% as opposed to 46%, 29% and 20% of its population.

The 4 degrees Celsius rise can prove disastrous for cities like Shanghai and Shantou in China; Howrah district in Calcutta and Mumbai, by submerging land inhabited by half or more of today's population.

Howrah district in Calcutta, which lies next to the Hooghly river, where 60% population is at risk, would benefit by the 2 degrees Celsius difference in the warming scenario. The risk would be cut three-fold, as would Wuxi, a city near Shanghai, China on the banks of the Taihu Lake.

However, the Asian megacities of  Shanghai and Hong Kong in China and Mumbai in India, in spite of limiting the temperature rise to 2 degrees Celsius, would still have 25% of its lands submerged in the impending rise in sea level.

At the UN summit, the Paris Climate Conference - COP21, to be held in December 2015, issues that would determine the future of climate change and management, and lives of millions of people in the world would find expression. The aim of the conference would be to legally bind more than 190 countries to a universal agreement on climate, with the aim of keeping global warming below 2°C.