The waters of the world are rising, but by how much and where?


Earlier this year, climate activists held a funeral for the Okjökull glacier. His tombstone, the first of its kind, is on top of a volcano in Iceland, where the ice sheet has melted at an unprecedented rate(waters of the world are rising). In fact, if all the ice in Iceland melts, it could raise the sea level around the world about five feet. And by the end of this century, as more glaciers recede and melt, the sea level could rise by two full meters. That is roughly the height of a door.

Recently, Scott Kulp and Benjamin Strauss, two climate scientists from Climate Central, an American nonprofit organization dedicated to climate research, identified the areas most vulnerable to the projected rise in sea level by 2050 and 2100. They released maps showing parts from Mumbai, Chennai and Calcutta, and other cities in South Asia, plunging into the next three decades, suggesting that around 300 million people are vulnerable if humanity continues to emit more carbon.

The waters of the world are rising, but by how much and where?

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This is approximately triple the number of people estimated to be vulnerable in an old model that works with the same emission trends.

The significant mismatch arises from how scientists evaluate the elevation of the earth. A more accurate prediction requires more accurate elevation data. In the early 2000s, scientists obtained NASA’s Shuttle Radar Topography Mission (SRTM) numbers to approximate the risk of flooding in coastal areas. “But SRTM data is flawed,” Kulp told The Wire. Technology cannot distinguish trees from buildings and other characteristics of the land, so the average reported elevation of an area may be very different from reality. Errors can reach up to 2 m in low coastal areas.

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A more accurate way to calculate the elevation of the terrain is through the use of light and range detection (LIDAR). In a land survey based on LIDAR, scientists connect a laser to an airplane, drone or helicopter and emit light to the ground. The reflected signal indicates how the ground rises and falls as the air vehicle moves over it. On the other hand, LIDAR is expensive and, therefore, most Asian countries, whose economies are more vulnerable to the vagaries of climate, have no LIDAR data.

To solve this, Kulp and Strauss used machine learning. They trained a neural network to identify failures in SRTM data for the United States coast by comparing it with more than 50 million LIDAR data points in the same area. Once the network had “learned” how SRTM and LIDAR data matched, they converted SRTM data around the world into more accurate digital elevation data, called coastal DEMs, where they estimated the errors were of the order of 10 cm or less.

And when the duo overlaid the sea level rise model in the coastal DEM, they discovered that older models had underestimated the risk of flooding. According to the coastal DEM, they discovered that without coastal defenses, 360 million people would be vulnerable to flooding by the year 2100 if sea levels continued to rise as predicted by the models.

Kulp and Strauss also stressed that this would be the case even if all countries adhered to the terms of the Paris Agreement. If economies do not reduce carbon emissions and if the Antarctic ice sheet begins to disappear, 480 million people will be vulnerable to flooding by 2100.

The carbon dioxide we release into the atmosphere traps heat, driving global warming. Historical data shows that global sea levels have increased more rapidly since humanity began burning coal and oil as fuel. Between 1900 and 2000, the average sea level increased by approximately 1.7 mm each year. After 2000, it jumped at about 3 mm / year. The scientists recorded a similar trend for the Indian Ocean, except in the North Bay of Bengal, where sea levels increased by 5 mm/year between 1948 and 2010 (as estimated in 2015).

But the claim that certain neighborhoods within cities could be submerged does not retain water(waters of the world are rising).

According to the maps published along with the duo’s document, many areas in Mumbai, Kolkata, and Chennai could sink by 2100. However, many of these areas also appear to be about 8-10 m above sea level.

These predictions are also limited by the fact that they do not take into account the embankments and defense structures that governments have erected to protect the coast from high tide lines. According to the document, about 110 million people in the world and about 17 million people in India already live below these lines.

But Kulp flips the threat to find a positive side: “Our results give hope that living with high tide lines is feasible,” although if the sea level rises, even more, more people could be exposed to extreme storms and floods.

For example, some parts of Mumbai have always been at or below sea level, so the worst typical scenario when the sea level is higher would be flooded due to extreme rains during high tide. “Such events, called compound events, have the potential to submerge large parts of Mumbai, at least for several days,” Koll said.

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And if seawater moves inland, it can damage the soil considered useful for agriculture and even facilitate the spread of diseases. In 2015, doctors in Bangladesh were able to associate the spread of cholera with the intrusion of seawater. In another analysis published the same year, scientists reported that “the appropriate areas for Vibrio cholerae, “the bacteria that cause cholera in humans,” is expected to increase under the future climate,” even in the eastern coastal areas. from India and Latin America.

Through this study, we want to pressure economies and countries to take note of the problem and understand the importance of coastal elevation data,” said Kulp. He and others argue that such data will help countries assess risk more realistically and better plan extreme events.

Another way of looking at the study is to realize that reducing emissions will help three times more people,” he added. “And that investing in green technology is three times more justifiable.”



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