Science Matters to come closer to truth!
Essay by S. Tom Bond, Resident Farmer & Retired Chemistry Professor, Jane Lew, Lewis County, WV
The U. S. has experienced four hurricane disasters just this past year: Harvey in Texas and Louisiana in August; Irma, a particularly intense hurricane with winds of 185 miles an hour in the Caribbean reached south Florida in early September. Jose hit the East Coast of the U. S in late September. Maria, the most damaging on record in Puerto Rico and the Virgin Islands occurred in late September. Combined they cost $200B. The Atlantic had 17 named storms in 2017. See storm tracks here.
What is a hurricane? It is a violent storm the size of a tropical cyclone having sustained winds of over 74 miles per hour. There are five categories, defined by wind speed. When they move over land devastation is proportional to wind speed.
What causes a hurricane? The best answer requires a little bit of science. Water vapor is formed when water evaporates. It takes heat to overcome the attraction between water molecules that causes them to stick together to be a liquid. When enough energy is supplied, they can separate and each molecule goes it’s own way, up into the air. That moist air is lighter and tends to rise. As the reader knows, higher in the atmosphere the temperature goes down. When a mass of humid air reaches an altitude where it is cold enough, the heat is transferred to the air. The warmed air continues to rise, and the water condenses and falls out as rain. This is the source of rain and snow.
A tremendous amount of heat is needed to evaporate water, over five times as much as is needed to warm the water from the freezing point to the boiling point. This is released when it condenses back to water (rain). If a smaller mass of air hits a really cold layer, a thunderstorm results. If a moist area goes up to a cool, but not very cold air mass, rain occurs.
When very humid air over the ocean in a wide area rises to a cold level, it continues to rise as it drops rain. This rising draws up more humid air from below. The warm air spreads out in the upper atmosphere, forming a whirling cloud cover. More and more heat is drawn from the ocean’s top layer as the system spreads out. Winds rising in the interior of the system go faster and faster. Up, up, up, driven by rain condensing out. When they reach 74 mph it is a hurricane.
This happens only over the ocean. Evaporation from land does not provide enough heat and moisture. The ocean absorbs 90 to 95% of the heat causing the earth’s temperature rise. More on ocean temperatures here. Of course evaporation occurs over any body of water and wet land, but only the warm ocean holds enough heat to form a hurricane.
The warmer the ocean surface, the more heat is available to supply humidity for the air. Extra heat is provided to the ocean by global warming. The air over it has more water content, and there is more reserve heat to keep on evaporating more water. The heat removed from the ocean surface may cool it enough to cause the storm to weaken it. If the hurricane moves over land, it dies out because heat is not available to continue to drive it.
The effects of global warming are not understood just as a warming of the earth. Many of the phenomena damaging our environment and our economic situation must be interpreted in terms of heat moving from one place to another.
See also: NASA: Climate Change and Global Warming
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