![]() ![]() Right now it’s the feeblest it’s been in more than 1,000 years.Ī shutdown of that ocean current could dramatically alter phenomena as varied as global weather patterns and crop yields. ![]() As more glacial fresh water enters the system, that conveyor belt will weaken. The water’s salinity increases as it evaporates, which, among other factors, makes it sink and return south along the ocean floor. The AMOC is like a conveyor belt, drawing warm water from the tropics north. When melt from Greenland’s glaciers enters the ocean, for example, it alters an important system of currents called the Atlantic Meridional Overturning Circulation. But some tipping points will interact, worsening one another’s effects. The fate of the Thwaites Glacier could be independent of other tipping points, such as those affecting mountain-glacier loss in South America, or the West African monsoon. ![]() How that plays out will help determine how much sea levels will rise-and thus the future of millions of people. At a certain point, that melt may progress enough to become self-sustaining, which would guarantee the glacier’s eventual collapse. Although the ice shelf’s overall melt is slower than originally predicted, warm water is now eating away at it from below, causing deep cracks. ![]() Take the Thwaites Glacier in West Antarctica: It’s about the size of Florida, with a protruding ice shelf that impedes the glacier’s flow into the ocean. Some natural systems, if upended, could herald a restructuring of the world. On the whole, however, the implications of blowing past these tipping points remain among climate change’s most consequential unknowns: We don’t really know when or how fast things will fall apart. If these thresholds are passed, some of global warming’s effects-like the thaw of permafrost or the loss of the world’s coral reefs-are likely to happen more quickly than expected. “The Earth may have left a ‘safe’ climate state beyond 1☌ global warming,” Armstrong McKay and his co-authors concluded in Science last fall. In fact, a growing number of climate scientists now believe we may be careening toward so-called tipping points, where incremental steps along the same trajectory could push Earth’s systems into abrupt or irreversible change-leading to transformations that cannot be stopped even if emissions were suddenly halted. “And it has happened fast enough that people have a memory of it happening.” And now we’re really not,” Allegra LeGrande, a physical-research scientist at Columbia University, told me. “For a long time, we were within the range of normal. Early July brought the hottest day globally since records began-a milestone surpassed again the following day. Vermont saw a deluge of rain, its second 100-year storm in roughly a decade. The Southwest is sweltering under a heat dome. Its impacts, however, are accelerating-sometimes far faster than expected.įor a while, the consequences weren’t easily seen. For decades, climate change has proceeded at roughly the expected pace, says David Armstrong McKay, a climate scientist at the University of Exeter, in England. Ever since some of the earliest projections of climate change were made back in the 1970s, they have been remarkably accurate at predicting the rate at which global temperatures would rise. ![]()
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