Sci&Tech Writer Daniel Bray explains new research concerning climate change and rising sea levels

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If we look back to last week’s flooding in Yorkshire and Derbyshire, which has so far claimed the life of one woman, it’s clear that the current climate emergency is not simply a matter of unprecedented global warming – it’s also the issue of an increasing number of serious weather events occurring. Scientists Scott Kulp and Benjamin Strauss have just given us more cause for concern, with a recent paper published in Nature Communications which claims that many more areas of the world are at risk of flooding than we originally thought.

Previously, when assessing the impact of water level rises, we used global elevation data from NASA’s Shuttle Radar Topography Mission (SRTM), a model created by a specially-made radar system that flew with Space Shuttle Endeavour in February 2000. The flaw with SRTM is that it models the elevation of upper surfaces, and not bare earth terrain. This means that, in densely populated areas especially, there is a lot of data accounted for by human structures. In the US, the average error in the readings compared to more accurate lidar calculations was 3.7m, and in Australia it’s 2.5m, between elevations of 1 and 20 meters above sea level. This margin of error means that when calculating the impact of extreme coastal water level exposure, our estimates were actually quite large underestimates. 

In the US, the average error in the readings compared to more accurate lidar calculations was 3.7m

In order to get a more accurate look at how the earth will be affected by rising sea levels, Kulp and Strauss created a new digital elevation model called CoastalDEM. Their model used a neural network to perform analysis of the error in SRTM. In some cases, such as in densely populated coastal cities in the US – including Boston, New York City and Miami – they were able to reduce vertical bias from 4.71m to 0.06m.

This improved data produced some scary results – roughly three times as many people are at risk of being exposed to rising sea levels than previously thought. In a conservative scenario, where the world warms by only 2°C and the ice sheets don’t collapse, 150 million people are living on land that will be below high tide by 2050. 70% of these people at risk are from only eight Asian countries: mainland China, Bangladesh, India, Vietnam, Indonesia, Thailand, the Philippines and Japan.

The danger of these sea level rises is not confined to Asia – there are 19 countries with over one million people at risk of permanent inundation by 2050, including the United Kingdom, without the intervention of producing flood defences.

There are 19 countries with over one million people at risk of permanent inundation by 2050, including the United Kingdom

It is important to note this last point – both the new and old models do not take into account manmade flood defences – if we take the Netherlands, for example, we can see that a large portion of the country is at risk in both models, but as they have extensive flood defences, we cannot say whether or not they will see the worst of the predicted impacts. This is surely the saving grace from this project – we can now see with greater clarity than ever where is most at risk of water level rises, and we have a golden opportunity to start protecting them, to prevent the possibility of a mass human dislocation.

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