Over 50 million people in China will be at risk from coastal flooding by the end of the century if greenhouse gas emissions continue to stay high, a new study finds.
The research shows Asian countries dominate a top-20 ranking of most vulnerable nations from rising sea levels, with China topping the list.
A team of researchers from the US climate news website Climate Central mapped sea levels around the world using a global database of tide gauge measurements. They then combined these measurements with projections of how much scientists expect sea levels to rise with climate change.
The result is an interactive map, showing the number of people in each country likely to be living with significant risk of flooding by the end of the century. The map can be adjusted for different scenarios of future carbon emissions and sea level rise.
The size of squares shows population at risk, while the colour indicates the proportion of total population at risk.
Global estimates of population number (square size) and proportion (square colour) at risk from coastal flooding by 2100 by country. Assumes current emissions trends continue, and a central estimate of sea level rise. New York Times
The map uses a ‘business-as-usual’ scenario that assumes carbon emissions continue to rise swiftly this century. Climate models project global sea level rise of between 52 and 121 cm for this scenario. The map takes a central estimate of 79 cm by 2100.
The researchers also present their results as a ‘top-20’ list, ranking countries by the total population at risk in 2100.
People living on land that will be below sea level or chronic flood levels by the end of the century, Assumes current emissions trends continue, and a central estimate of sea level rise. Climate Central
China has the largest population at risk, more than twice as many people as Vietnam, which sits at number two on the list.
European countries are quite prominent, with the Netherlands, UK, Germany, France and Italy in the top 20. The UK sits twelfth with over 2.5 million people predicted to be at risk of flooding by the end of the century.
While the study shows how many people could be at risk from coastal flooding in the future, it doesn’t consider the impact of measures that reduce flood risk, such as building flood defences.
Almost half of the population of the Netherlands could be at risk from flooding, the study notes. But the country has one of the most sophisticated flood protection systems in the world. As a result, the population exposed to increased flood risk is likely to be smaller.
But flood defences are expensive, with large upfront costs and continuous maintenance. London’s Thames Barrier, for example, cost over £500 million to build (about £1.6 billion in today’s money) and will require around £1.5 billion to maintain over the next 20 years.
Not all countries can afford to take similar measures to protect themselves, particularly those with large coastal populations to defend. When a similar study ranked port cities around the world according to population exposed to flood risk in 2070, they found 17 of the top 20 cities were in developing countries.
In addition to the business-as-usual scenario, the new research looks at two more optimistic scenarios, requiring ‘sharp’ and ‘extremely sharp’ reductions in carbon emissions.
They give an idea of how the numbers might change. The population at risk in China could be as low as 36 million by the end of the century. That’s if emissions are cut rapidly, and sea levels rise relatively slowly. Taking the most pessimistic view, the number of people at risk jumps to 62 million.
The study doesn’t take into account the likely increase in global population. Recent projections have suggested a 95 per cent likelihood of the world’s population rising to between nine and 13.2 billion by 2100.
Predicting the actual number of people at risk is hard and depends on population, and flood protection. But it illustrates this is a problem that’s only going to get bigger as sea levels rise.