Hurricanes have been described as Mother Nature’s way of telling us she is angry, her way of cleaning up, her way of shedding excess ocean heat and/or her way of transferring heat from the equator to the poles.
According to NASA, Hurricanes: Katrina and Rita in 2005 each cooled water temperatures of the Gulf of Mexico by more than 4°C in places along their paths, and cooled the entire Gulf by about 1 degree but these temperatures rebounded quickly.
When she is angry, as she is now, hurricanes draws heat from the surface to produce clouds that radiate heat towards the poles but she also mixes warm surface water deeper down from where much of the heat is returned within weeks back to the surface, where it is reheated by the atmosphere to pre-hurricane temperatures.
In this way, it is hypothesized hurricanes produce a positive feedback that strengthen subsequent storms that traverse the same segment of the ocean as appears to be happening now with Hurricanes Irma and Jose.
The ocean is made up of several layers. The mixed layer is the warmest because it is in contact with the atmosphere and the specific heat of water is much larger than air. The top 2.5 meters of the ocean holds as much heat as the entire atmosphere above it. To change the temperature of a mixed layer of 25 meters by 1°C, the atmosphere must be warmed by 10 °C and essentially that is what is happening now in the Atlantic.
The average temperature of the ocean surface waters is about 17°C. As the following NASA Earth Observatory visual of a few days ago shows the sea surface temperature is currently closer to 31°C in parts of the Gulf of Mexico and the Atlantic and the consequences of these temperatures in terms of hurricane categories.
The mixed layer of the ocean is shallow, often only about 10-20 meters deep, but below this the thermocline gets colder with depth and at 1000 meters the temperature is about 4°C virtually all across the oceans.
Essentially, therefore, less than a half of one percent of the ocean’s depth is being used as an effective storehouse of the ocean’s heat.
A 2010 study by Jansen et al., suggested that only about a quarter of the heat mixed downward by tropical cyclones eventually makes it into the permanent thermocline. The majority, three-quarters of the heat, is reabsorbed by the mixed layer and in the winter and spring months it is transported out of the tropics, toward the poles, where it is problematic in terms of sea level rise.
It was estimated in a 2001 study by Kerry Emanuel that on average, hurricanes contribute about one petawatt (equal to one quadrillion watts) of heat to the estimated two to four petawatts of heat the ocean transports out of the tropics toward the poles each year.
Lyman et al., in the Nature paper, Robust warming of the global upper ocean deduced that the upper layer of the ocean has warmed since 1993 by about 335 TW each year, enough energy to continuously power nearly 500 100-watt light bulbs per each of the roughly 6.7 billion people on the planet.
Instead of letting hurricanes transport this heat out of the tropics, at least a third of it needs to be sequestered in deep water to a depth of 1000 meters by moving it through heat engines, which in turn convert about 7.5% of this heat, 25TW, to productive energy.
Since the diffusion rate of heat sequestered at this depth is 4 meters/year, it takes about 250 years for this heat to return back to the mixed layer, at which time it can be recycled into more work rather than becoming fuel for future storms.
With a conversion rate of 7.5% this heat can be recycled 13 times while providing energy for the next 3300 years.
Instead of goading her, we need to work with Nature to maintain a liveable planet and to produce the energy required to address the other needs of mankind.
Damage caused by Hurricanes Irma and Harvey, and the forthcoming Jose, could cost Lloyd’s of London insurers £150 billion ($200 billion) and if you believe these are once in five hundred year event, you are dreaming. As the following graphic demostrates, although the Atlantic hurricane season runs from August to October, these storms are active somewhere virtually all year and can be harnessed constantly by grazing OTEC plants that feed of this natural source of energy.
www.aerospaceweb.org shows the classes of hurricanes and their destructive power in the following table.
Better than being catastrophic events, the fuel that powers hurricanes can be harnessed for the benefit of mankind.
A difference of 3oC sequestered in the right places and over decades can be the difference between a category 5 storm like Irma and no hurricane at all.