Between 470 to 760 million people could lose their homes to rising sea levels if carbon emissions meet or exceed 4°C of warming — the direction in which business-as-usual is heading — with unstoppable rises to occur over centuries, according to a new report and searchable interactive maps published by Climate Central.
Aggressive carbon reductions resulting in 2°C warming could bring the number as low as 130 million people, the report shows. The analysis comes as world leaders prepare to meet in Paris next month for COP21, which many hope will result in the first international, legally-binding climate change treaty.
To determine implications for all coastal nations and cities, the new Climate Central 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.
China is most at risk, with 145 million people living on land ultimately threatened by rising seas if emission levels are not reduced, the report finds. China also has the most to gain from limiting warming to 2°C, which would cut the total to 64 million.
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Twelve other nations each have more than 10 million people living on land at risk, including India, Bangladesh, Vietnam and Indonesia. Meeting the 2°C goal would reduce exposure by more than 10 million in each of these nations, as well as most others in the top risk group, including the U.S., Japan, the Philippines, Egypt and Brazil.
Vietnam, for example, has 46 million inhabitants on land endangered by 4°C warming, versus 26 million on land at risk from 2°C.
Global megacities with the top-10 largest threatened populations include Shanghai, Hong Kong, Calcutta, Mumbai, Dhaka, Jakarta, and Hanoi.
Although the sea level rise to realize these threats likely will unfold over hundreds of years, carbon emissions this century can lock in one path or another, the report says.
Alongside the report, Climate Central has created an embeddable global interactive, called Mapping Choices, which allows users to 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.
In recognition of the growing threat of climate change, several cities around the world have presented ambitious climate action plans in accordance with the planning and reporting requirements of the Compact of Mayors. Buenos Aires, Cape Town, Copenhagen, Melbourne, New York City, Oslo, San Francisco, Stockholm, Sydney and Washington, D.C. joined Rio de Janeiro on the list of cities to meet the Compact compliance milestone.