The Day After Tomorrow is Today

You may all remember that 2004 science fiction film, where a climatologist is ignored by world government officials when warning them that a gigantic superstorm was about to freeze up the northern hemisphere, which meant a catastrophic natural disaster. According to the film, the superstorm would come about due to the interruption in the normal circulation of ocean currents. Warm and cold water masses that moved north and south and that were capable of controlling world temperatures had been slowed down. The consequence of such phenomenon had catastrophic climatic effects. It forced billions of people to flee to the south, to equatorial regions in an attempt to avoid dying in the storm. As much as that film was fiction because such a climatic disaster would never occur in a matter of days, – at least not naturally – it is true that the currents exist, and now, according to scientists from Barcelona Supercomputing Center and the Department of Meteorology at the University of Readin in the UK, both Gulf currents and arctic water currents are indeed slowing down. As told in the film, the considerable slowing down of these currents would indeed affect and change weather patterns in western Europe, turning the region much colder, while southern regions would get warmer. The main system of ocean currents is slowing down, that is their conclusion. The mechanism that transports the warm waters of the Caribbean to the north and the cold polar to the south has been failing for decades. Although they do not agree on when the problems began or in the ultimate cause of the failures, they do know that the consequences are not good. These bodies of water are the true circulatory system of the planet, distributing heat, nutrients and gases. Neither the tides nor the wind are the main live forces of the sea. The influence of the first does not go beyond the coastline and, no matter how strong the second is, its force is not felt below the first 100 meters of depth. What really moves the water of the seas and oceans in the form of currents is something as basic as what weighs more sinks and what weighs less tends to stay up: density gradients. In the Atlantic Ocean, the current of the Gulf is an immense mass of warm waters, that is less dense and heavy. It travels north from the Caribbean, losing heat in the transfer. That fact tempers the climate of Western Europe. Meanwhile, in the opposite direction, the cold waters of seas such as Labrador, Barents or Greenland still become denser and heavier with the contribution of salt expelled by the advance of Arctic ice. They sink forming the so-called deep water mass of the North Atlantic then moves southward. Although the system is more complex, these elements are the main arteries of the Southern Circulatory System of the Atlantic (SCSA). This is the engine that is failing. “The SCSA has weakened in the last 150 years to levels never recorded in more than a millennium,” says climatologist and co-leader of the Barcelona Supercomputing Center climate prediction group, Pablo Ortega, co-author of one of the studies. The flow would have been reduced, according to estimates, between 15% and 20%. In absolute terms, the flow would have decreased by some 3 million cubic meters per second. To get an idea, all the rivers in the world discharge about 1.2 million cubic meters per second. “The decrease was very rapid and continues to fall, although at a slower pace,” adds Ortega, who participated in this research when investigating the SCSA in the meteorology department of the University of Reading. The flows of the oceanic currents did not begin to be measured until this century, so to determine its flow in the past it is necessary to resort to indirect measurements. In this research, published in the journal Nature, scientists analyzed the grain size of the sediments of the seabed: the larger, the stronger the currents must have been at that time to drag the finest. Other indirect data were records of water temperatures. “Our study offers the first comprehensive analysis of the ocean sediment record, showing that this weakening of the SCSA began shortly after the end of the Little Ice Age,” says in a note the researcher from the Woods Hole Oceanographic Institution and co-author of the work, Delia Oppo. This mini glaciation began in the fifteenth century and remained until the nineteenth. What researchers believe happened then is that the warming caused the melting of large layers of the Arctic region. So much fresh water altered the mechanism of the SCSA as a stopper: by diluting the sea water it reduced its density, slowing down its subsidence, which must have slowed the arrival of the warm waters of the south. The melting is also the possible causal mechanism pointed out by another group of scientists in their own study on the evolution of SCSA, also published in Nature. Like the previous work, here you have found a reduction in the flow of this system of currents of 15%. To obtain their results, they used climate models and available records of surface water temperature, of which data are available since the 19th century, as an indicator of water transfer. What is different is that this work fixes the beginning of the weakening at a more recent date, around 1950, and blames […]

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