We often hear a great deal from weather experts about how extreme weather is being made all the more intense by the rise in climate change, especially when it comes to events such as hurricanes, but we’re rarely given the chance to see just how much global warming is actually contributing to any given weather event. However, using composite maps from resources such as nullschool.net, we’re presented with a visual representation of how storms such as Hurricane Florence can change the temperature of the ocean’s surface as it passes overhead, to give us an idea how much energy is imparted to the storm. While it is not a proper scientific analysis by any stretch of the imagination, it appears that Florence’s approach to the US east coast was fueled almost exclusively by surplus heat generated by global warming.
One must bear in mind that these maps, known as sea surface temperature anomaly maps, are not thermographs, in that they do not show how hot the ocean’s surface is; rather, they illustrate how far from the twentieth-century average the temperature deviates in any given location. Black areas are in line with the norm, red/yellow areas are above average, while areas dipping into blue are below average. So while the image might initially appear to show that the waters off of the coast of Maine and eastern Canada are much hotter than the southern half of the eastern seaboard, the opposite is true, with the waters off of North Carolina being about 10 degrees warmer than those off of Massachusetts; rather, the temperature deviation from the norm is just that much more pronounced in the north than it is in the south.
The first image is of the western North Atlantic on September 03, 2018, while Florence was still only about 1,600 kilometers (1,000 miles) west of the Cape Verde Islands, off of the West African coast. At this point in time, the waters along Florence’s path range from 1ºC (1.8ºF) to 1.5º C (2.7ºF) above normal, peaking to 2.8ºC (5ºF) near the coast.
Florence’s path is clearly visible on the map complied from September 15, the day after Florence made landfall, graphically showing how much energy was imparted from the ocean surface to the passing hurricane. The swath of now-cooler water along Florence’s path now dips down more-or-less to the 20th-century average, with some spots reading as low as 0.5ºC (0.9ºF) below normal. The implication implied by these readings is that as Florence approached the US East Coast, it was fueled almost exclusively by surplus heat generated by global warming.
One must bear in mind that Florence itself wasn’t the product of global warming, as the hurricane was likely to form under normal conditions to begin with: if we take away the excess temperature from the water along Florence’s path it still maintained the 26.5ºC (79.7ºF) minimum needed to sustain a hurricane. Rather, what we’re seeing here is the influence climate change can have on weather events, especially ones as extreme as a hurricane. Although Florence weakened to a category-1 storm before it made landfall, much like hurricane Harvey from the previous year it was stalled by a high-pressure ridge over the Carolinas and West Virginia, dumping record rainfall on the region that resulting in massive flooding that still inundated many regions over two weeks later. Florence was responsible for the deaths of 48 people, over $38 billion in damage, and an ongoing list of environmental catastrophes caused by the spilling of waste products into the floodwaters.
The waters off of the Eastern Seaboard are particularly vulnerable to the effects of climate change: increasing amounts of freshwater from melting glaciers in Greenland are dumped into the North Atlantic, disrupting the North Atlantic Current, causing warm water that would normally flow northeast from the Caribbean to pool up off of the east coast. In terms of its effect on hurricanes, this warm water adds more energy and moisture to already-extreme storms; and as the water warms it expands, raising sea levels in the area, compounding the effect of storm surges.
Once again, this is not a scientific analysis, but rather meant to be a visual representation of how much energy is imparted to a storm from the ocean’s surface. The maps themselves are, however, accurate, compiled from the National Oceanic and Atmospheric Administration’s Real-Time Global Sea Surface Temperature (RTG-SST) Anomaly data, the National Centers for Environmental Prediction (NCEP), and the US National Weather Service.