Rising sea levels: a new modelling approach

Last month, a study by Climate Central claimed that the number of people under threat by rising sea levels by 2050 is three times greater than previously understood. But there is reason to be optimistic: IF Junior Researcher Melissa Bui explains how a new modelling approach can help us understand how to best respond to human migration as sea levels rise

One of the top concerns and perhaps the easiest consequence of global warming to conceptualise is rising sea levels. Computer models have served as an important tool for researchers striving to simulate the social implications of rising sea levels, one of the most famous examples being NASA’s Shuttle Radar Topography Mission (SRTM) in 2000.

More recent, improved estimates are telling us that the stakes associated with meeting climate-change targets are much higher than previously understood. According to a new paper by Climate Central, 150 million people are currently living on land which will be below high-tide levels by 2050 – approximately 40 million higher than previous estimates. An interactive map also developed by the researchers shows the newly-identified highly-populated, low-lying areas of land that are most at risk, namely in Asian countries such as China, Bangladesh, India and Vietnam.

How high are the stakes?

According to the Climate Central paper, land currently home to 150 million people at present will be below high tide lines by 2050, and 360 million people will also be vulnerable to annual flood events by the end of the century. This is the prediction under a moderate scenario of global emissions, where global warming is sustained at 2°C and the Antarctic is stable.

But if global greenhouse emissions were to continue unchecked and the Antarctic was unstable, this figure rises to a staggering 340 million people living under high water lines by the end of the century. These estimates dwarf those presented in the SRTM.

It’s clear that the amount of land that will become dangerous as sea levels rise will be much greater than we previously thought. The question looming on policy-makers’ minds is: what can we do about it? The study suggests that we have the ability to minimise the number of people at risk. According to the researchers, if we were to limit global warming to just 1°C higher than global temperatures in the 1990s, we could reduce the number of people living under the high tide line by 2100 to 190 million.

But even under this scenario – which would require rapid and steep cuts in global emissions from both developed and developing countries – there would still be millions of people to protect. The system in place at present is certainly not effective enough; among the 110 million people already living below current annual high tide levels, many live without any type of coastal protection.

Rising sea levels and human migration

The challenge of responding to rising sea levels is also complicated by numerous factors, one being human migration. Policies need to be able to respond appropriately to human migration induced by rising sea levels. But as a recent paper produced by a group of international scholars has stressed, policies also play a key part in determining when and where climate-induced migration occurs, even if one is not facing the immediate physical danger of sea-level change.

For instance, policies and investments in coastal protection can influence the physical, economic and legal feasibility of migration as well as how attracted people are to their local neighbourhoods relative to more elevated ones.

It’s time for a new modelling approach

According to the researchers, a new modelling approach can aid our understanding of how policy decisions will impact human migration as sea levels rise. It involves going beyond predicting migration responses under different global emission scenarios; computer models developed for this purpose should also simulate migration responses to current and expected adaptation policies, paying attention not only to who is expected to migrate, but also where they might relocate to.

They also emphasise that this approach helps to build a realistic picture of future migration outcomes for policy-makers without having to experiment on these vulnerable populations in the real world. Computer models therefore seem to be not only an efficient tool for researchers and policy-makers, but also a safe one.

As the lead researcher, David Wrathall, explains, “Right now, people are actually moving toward coastlines that will be more and more vulnerable as the planet warms. The only thing that will change this trend is policy. If we start changing the incentives to live, work and invest in safer places, we could make sea level rise-induced migration less expensive and disruptive down the line.”

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