Remember earlier this year when the biggest Saharan dust cloud in decades drifted over the Atlantic and headed towards the US? In an unexpected twist, scientists now suspect that this unusual phenomenon might have been the creation of warming in the Arctic and sea ice loss.
In a new study, researchers at the Scripps Institution of Oceanography at the University of California, San Diego and Khalifa University of Science and Technology in the United Arab Emirates attempted to piece together how the so-called “Godzilla" dust storm of 2020 came to be.
The record-breaking Saharan dust cloud traveled on the Saharan Air Layer, a layer of baking hot and dry air typically formed between late spring and early autumn, peaking in late June to mid-August. While this occurs every year, the dust storm of June 2020 was a record-breaker. Reaching an altitude of 6,000 meters (19,600 feet), its thickness was double what had ever been recorded by satellites. The dust cloud event hit the Americas after a long journey across the Atlantic Ocean from the Saharan desert of Africa.
But what created such a fearsome force of nature? Writing in the journal Geophysical Research Letters, researchers argue that the freakishly large dust cloud was the product of a circumglobal wavetrain, a chain of wind patterns that roll through much of the planet, that might have its origins in reduced summertime Arctic sea-ice extent.
In short, they argue the low Arctic sea ice extent observed in June 2020 kicked off a chain of events that had a domino effect on wind patterns across many parts of the world. As part of this chain of events, high pressure and strong winds from the Arctic swooped down farther than typical in a clockwise direction, creating the development of a type of high-pressure system (a subtropical high) near the coast of West Africa. With lower pressure beneath this area, there was an intense north-south pressure gradient hanging over West Africa, creating extremely strong and persistent northeasterly winds that gusted around the Sahara. This, they say, caused anomalously strong northeasterlies over the Sahara, which kicked up dust for over four days before launching across the Atlantic.
“As the Arctic sea-ice cover was rather low in June 2020, around the lowest on record in the period of satellite observations, it may have contributed to the observed large-scale anomaly pattern,” the study concludes. “Thus, if such patterns become more common in a warmer world, it is plausible that these extreme dust outbreaks will increase in frequency in the future.”
However, this idea might prove to be controversial among some scientists. There’s an ongoing debate about the extent to which Arctic warming affects wider wind patterns. Some argue that the patterns seen in recent years are within the range of natural variability and should not be considered the product of climate change.
Furthermore, this new hypothesis challenges some existing ideas about how dust clouds affect hurricanes. There’s a strong amount of evidence to suggest that increased dust suspended over the Atlantic can reduce the numbers of tropical cyclones through dust-induced cooling of ocean surface temperature. However, despite the high levels of dust seen this summer, this year’s Atlantic Hurricane Season was the most active on record.
“Either 2020 is just a year where everything is upside-down, or we really need to reevaluate our understanding of how dust impacts that climate system,” Amato Evan, study author and atmospheric scientist at Scripps, said in a statement.