The US East Coast could soon be pounded by more intense and destructive hurricanes than ever before. The cause: greenhouse gases, which researchers say are disrupting patterns of air circulation known as wind shear.
Wind shear – a change in the speed or direction of the wind as it travels – can restrict the impact of a hurricane by diffusing it across a wide area. Historically, there is a high wind shear present across the US’s Atlantic Coast, helping prevent storms from growing too rapidly.
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A team from the US National Oceanic and Atmospheric Administration (NOAA) and Columbia University’s Lamont-Doherty Earth Observatory worked on models that demonstrate the two main factors for determining a storm’s strength and intensity: the surface temperature of the ocean and wind shear. The higher the temperature of the water, the more powerful a hurricane is likely to be - but a strong wind shear will act like a barrier, limiting the storm's intensity.
Now a link has been observed between rising levels of atmospheric CO2 – and other greenhouse gases – and weakening vertical wind shear along the East Coast of the US. That will make it less likely that recent violent episodes of extreme weather will start to dissipate after making landfall, and may instead grow in strength.
Some of the most destructive storms to hit the US during its annual hurricane season – 1 June to 30 November – have occurred in recent years at increasingly intense levels. The 2018 season was initially forecast to be at or around normal levels; a typical season contains 12 named storms, six hurricanes, and three major hurricanes. And the same forecast has been applied to the 2019 season by the NOAA.
But last year’s weather unexpectedly unleashed two particularly devastating storms in the Atlantic Basin: Hurricane Florence and Hurricane Michael. The two storms left nearly 100 people dead and caused damage worth several billions of dollars. Since 2000, there have been 16 above-average hurricane seasons, where intensity or duration were greater than expected. And the NOAA and Columbia researchers say that, in light of their predictions regarding wind shear change, that’s a pattern that could become more commonplace.
Meanwhile, the season is also starting earlier. This year, like last year and the four prior years, a tropical storm has been detected and named during May. In 2018, Storm Alberto formed on 25 May and this year, Storm Andrea was named on 20 May.