Carbon emissions causing 4°C of warming - what business-as usual points toward today - could lock in enough sea level rise to submerge land currently home to 470 to 760 million people, according to a report and searchable interactive maps published today by Climate Central, with unstoppable rises to unfold over centuries.

The research organization’s report also shows that aggressive carbon cuts resulting in 2°C warming could bring the number as low as 130 million people. The analysis comes as ministers from more than 80 countries meet in Paris to find more common ground weeks ahead of global climate talks in December.

Climate Central’s report builds on a US focused paper published last month in the Proceedings of the National Academy of Sciences of the USA, authored by Climate Central scientists Benjamin Strauss and Scott Kulp, and Anders Levermann of the Potsdam Institute for Climate Impact Research.

To assess implications for all coastal nations and cities, the new research uses relationships between warming caused by carbon emissions, the long term global sea level rise it locks in, and global elevation and population data.

The report finds that China is most at risk with 145 million people living on land ultimately threatened by rising seas if emission levels are not reduced. China also has the most to gain from limiting warming to 2°C, which would cut the total to 64 million.

Twelve other nations each have more than 10 million people living on land at risk, led by India, Bangladesh, Vietnam, and Indonesia.

Meeting the 2°C goal would reduce exposure by more than 10 million in each of these nations, plus most others in the top risk group, including Japan, the US, the Philippines, Egypt, and Brazil.

Vietnam has 46 million inhabitants on land endangered by 4°C warming, vs. 26 million on land at risk from 2°C.

The sea level rise to realize these threats will likely unfold over hundreds of years, but carbon emissions this century can lock in one path or another. “The global stakes of climate change are crystal clear with sea level rise,” said Strauss, PhD, Vice President for Climate Impacts at Climate Central and the lead author of the report.

“The outcome at Paris can point us toward losing countless great coastal cities and monuments around the world, unending migration, and destabilization, or toward preserving much more of our global heritage, and a more stable future.”

Levermann, Co-chair of the Research Domain Sustainable Solutions at the Potsdam Institute for Climate Impact Research in Germany, added, “Sea-level rise is nothing to be afraid of, because it is slow, but it is something to be worried about, because it is consuming our land, including the cities in which we create our future heritage today.”

Global megacities with the top-10 largest threatened populations include Shanghai, Hong Kong, Calcutta, Mumbai, Dhaka, Jakarta, and Hanoi.

Hanoi has 7.6 million on land at risk (0.6 per cent of the greater urban area population) after 4°C of warming, a number that drops to 3.6 million in the case of 2°C warming. Median projections of locked-in sea level rise are 9.2 meters for 4°C and 4.9 meters for 2°C.

In conjunction with the report, Climate Central has created an embeddable global interactive, called Mapping Choices (choices.climatecentral.org). Users can type in any coastal city name or postal code worldwide, and compare the potential consequences of different warming or emissions scenarios on a local basis.