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Scientists project that on average, the world’s oceans will rise about 3 feet by 2100, putting low-lying areas in danger, contaminating water supplies and undermining roads, airports, port facilities and power plants. But even this dire prediction isn’t severe enough to describe what is happening on the east coast of the United States, where sea levels are rising at an even faster rate. According to a new study in the February Journal of Geophysical Research, this is because the Gulf Stream (which moves north and then east toward northern Europe and usually regulates sea levels in the region) is slowing down due to the effects of global warming.
The study includes measurements of the Gulf Stream’s flow, from instruments mounted on underwater cables that stretch across the Florida Strait. The researchers also utilized satellite altimeter data to document changes in the height of the ocean from one side of the Gulf Stream to the other. Normally, the northeasterly flow of the stream literally pulls water away from the coast and keeps coastal sea level a meter or a meter and a half lower than the rest of the ocean. In recent years, however, the satellites show that the midpoint of the Gulf Stream doesn’t have as high an elevation as it used to, and that the edges aren’t quite as low—providing evidence that the stream itself is starting to slow down.
Ordinarily, the Gulf Stream brings warm surface water from the tropics up along the U.S. coast, and then across to the eastern North Atlantic, where it cools and sinks to the bottom of the sea. The cold bottom water then flows south to the tropics, where it gradually warms, rises to the surface, and begins flowing north again. This constant flow, which meanders through all of the world’s oceans is sometimes called the “global ocean conveyor belt”. Due to global warming, two things are happening to throw the conveyor belt off kilter. First, melting ice, mostly from Greenland, is diluting the surface waters where the Gulf Stream reaches its northernmost extent. Since fresh water is less dense than salty water, the water has a more difficult time sinking to begin its journey southward. And second, the surface water is warmer than it used to be, and since warm water is less dense than cold water, this just adds to the problem. These two issues together are slowing down the conveyor belt noticeably.
This prompts concerns that the slowing Gulf Stream will raise sea levels on the east coast even more than the average 3 feet in 90 years. And this could mean that east coasters can expect more extreme weather events and flooding as global warming takes its toll on the natural regulating systems of the world’s oceans.