Unusual mangroves far from the coastal zone portend future sea-level rise

Unusual mangroves far from the coastal zone portend future sea-level rise

past sea levels

Throughout its history, the Earth has experienced massive climate change driven by changes in its unstable orbit. Sometimes the planet tilts closer to the sun and absorbs heat more efficiently. At other times, the Earth’s orbit has stretched along an axis away from the heat of the Sun. In response, global temperatures have risen and fallen.

These temperature changes have drastic effects on sea level. During the Great Ice Ages, such as the one that hit the planet about 20,000 years ago, giant ice sheets covered North America as far as the Great Lakes and Long Island. The ice in Antarctica has extended beyond its current limits. The ice trapped huge amounts of water, bringing sea level down. The cooler oceans were also smaller, sometimes extending miles from their current locations. On the other hand, during the warm ages, the ice melted and the ocean waters spread, causing the sea level to rise.

Earth’s last warm phase reached its peak about 120,000 years ago, when global temperatures nearly reached 0.5 to 1.5 degrees degrees Celsius higher than it was before the industrial revolution. This is on the order of about 1°C above the average pre-industrial periods of global warming to date. Most of the countries that signed up to Paris Agreement It agreed to limit overall warming to less than 2°C or, if possible, to less than 1.5°C.

“The world was not very different in terms of climate,” says Alex Sims, a geologist at the University of California, Santa Barbara who has studied sea level history in the Gulf of Mexico. “Does this mean that you can expect a sea level rise of five meters or higher in the next thousand years or more?”

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The differences are very important. Just one meter of height can submerge vast stretches of the coast that contain large cities, economic centers and cultural resources. Currently, about 770 million people They live at altitudes less than five meters above sea level. A height of nine or 10 meters would be disastrous. Therefore, any data that can help determine what happened in the past can help researchers make more accurate predictions of future risks.

What levels have the seas actually reached?

It is very difficult to determine the sea level more than 100,000 years ago, when the ancestors of this mangrove swamp took root. Researchers often look for evidence of ancient coastlines, such as coral reefs or sand dunes. Next, they measured the distance between this evidence and the current coastlines to determine the difference in sea levels. However, there are several issues that complicate this calculation, such as changes in tides and local geological formations. The origin of the ice melt – Greenland and Antarctica, for example – may affect sea level records at remote sites.

Mangroves are found in the lake at an altitude of more than nine meters above the current sea level. The team also found some geological evidence: one of the families was digging a well near the site, and at a depth of a few meters they found a thick layer of shells and sand, which the researchers confirmed was part of an ancient beach about 10 meters high. sea ​​level.

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About the Author: Camelia Kirk

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