Note: City locations are incorrect in all the images
The New York Times reports on the weakening of the Gulf Stream Ocean current and what effects on climate that is likely to cause. Warm water off the West African coast crosses to Brazil and then moves north through the Gulf of Mexico and then up the east coast of the US and on up to Canada. The amount of water involved is huge. The current flow from Canada to Europe is slowing due to the ice melt in Greenland. That ice melt is producing a vast cold blob in the North Atlantic that is slowing the flow to Europe. Concerns by climate experts about the slowing of the Gulf Stream have been voiced for at least the last 15 years. A 2005 research paper provides some context for the concern:
The Atlantic meridional overturning circulation carries warm upper waters into far-northern latitudes and returns cold deep waters southward across the Equator. Its heat transport makes a substantial contribution to the moderate climate of maritime and continental Europe, and any slowdown in the overturning circulation would have profound implications for climate change. A transatlantic section along latitude 25° N has been used as a baseline for estimating the overturning circulation and associated heat transport. Here we analyze a new 25° N transatlantic section and compare it with four previous sections taken over the past five decades. The comparison suggests that the Atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004. (emphasis added)
IT’S ONE OF THE MIGHTIEST RIVERS you will never see, carrying some 30 times more water than all the world’s freshwater rivers combined. In the North Atlantic, one arm of the Gulf Stream breaks toward Iceland, transporting vast amounts of warmth far northward, by one estimate supplying Scandinavia with heat equivalent to 78,000 times its current energy use. Without this current — a heat pump on a planetary scale — scientists believe that great swaths of the world might look quite different.
Now, a spate of studies, including one published last week[1], suggests this northern portion of the Gulf Stream and the deep ocean currents it’s connected to may be slowing. Pushing the bounds of oceanography, scientists have slung necklace-like sensor arrays across the Atlantic to better understand the complex network of currents that the Gulf Stream belongs to, not only at the surface, but hundreds of feet deep.
“We’re all wishing it’s not true,” Peter de Menocal, a paleoceanographer and president and director of the Woods Hole Oceanographic Institution, said of the changing ocean currents. “Because if that happens, it’s just a monstrous change.”
The consequences could include faster sea level rise along parts of the Eastern United States and parts of Europe, stronger hurricanes barreling into the Southeastern United States, and perhaps most ominously, reduced rainfall across the Sahel, a semi-arid swath of land running the width of Africa that is already a geopolitical tinderbox.
The scientists’ concern stems from their understanding of thousands of years of the prehistoric climate record. In the past, a great weakening or even shutdown of this arm of the Gulf Stream seems to have triggered rapid changes in temperatures and precipitation patterns around the North Atlantic and beyond.
The northern arm of the Gulf Stream is but one tentacle of a larger, ocean-spanning tangle of currents called the Atlantic Meridional Overturning Circulation, or AMOC. Scientists have strong evidence from ice and sediment cores that the AMOC has weakened and shut down before in the past 13,000 years. As a result, mean temperatures in parts of Europe may have rapidly dropped to about 15 degrees Celsius below today’s averages, ushering in arctic like conditions. Parts of northern Africa and northern South America became much drier. Rainfall may even have declined as far away as what is now China. And some of these changes may have occurred in a matter of decades, maybe less.
The AMOC is thus a poster child for the idea of climatic “tipping points” — of hard-to-predict thresholds in Earth’s climate system that, once crossed, have rapid, cascading effects far beyond the corner of the globe where they occur. “It’s a switch,” said Dr. de Menocal, and one that can be thrown quickly.
Some people still deny climate change is associated with polluting human activity. That is a shocking false belief that ranks up there with the false belief some people still have that the ex-president won the 2020 election. The seeds of human self-delusion and self-annihilation are firmly rooted in the evolution of the human mind.
Footnote:
The Atlantic Meridional Overturning Circulation (AMOC)—one of Earth’s major ocean circulation systems—redistributes heat on our planet and has a major impact on climate. Here, we compare a variety of published proxy records to reconstruct the evolution of the AMOC since about AD 400. A fairly consistent picture of the AMOC emerges: after a long and relatively stable period, there was an initial weakening starting in the nineteenth century, followed by a second, more rapid, decline in the mid-twentieth century, leading to the weakest state of the AMOC occurring in recent decades.
In this article, using several different and largely independent proxy indicators of the AMOC evolution over the past 100 to nearly 2,000 years, we provide strong evidence that the AMOC decline in the twentieth century is unprecedented and that over the past decades, the AMOC is in its weakest state in over a millennium.
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