Category 7 is off the Saffir-Simpson scale, though after Hurricane Dorian, it is clear that Saffir-Simpson is inadequate. The current most powerful grading for a hurricane is Category 5.
Science warned us a few decades ago about the future effects of greenhouse gas emissions, yet those predictions now seem grossly inadequate, the results of a tentative and cautious approach, a consequence of the time it takes to do good science.
Science did alert us to the historical and causal connections between greenhouse gas emissions and global warming. Yet if we do history so well, why can't we predict the future? In the end, intuition, and hard science cede to the ultimate source of results, nature herself.
In 2011 I wrote how storms and wildfires would worsen as our species continues to dump greenhouse gasses (CO2 and methane primarily) into the atmosphere.
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| NASA chart displaying ppm C02 from 800,000 years ago to the Present |
The above chart by NASA illustrates measurements from Antarctic ice cores, of atmospheric C02 levels from 800,000 years ago to the present day. Compiling this data alone represents an amazing feat of science.
Earth passed through many cycles of relatively high and low carbon dioxide gas levels, but the data clearly illustrates that the highest levels during that nearly million year period are occurring now, during our present age. We are literally dumping CO2 into the heavens. This translates into a hotter earth, and much stronger storms.
Climatic heat change is not even, nor is it absorbed equally by land, sea or air, or by any portions thereof. Uneven warming exacerbates the strength of storms of all types.
Today's entry was written as the very powerful Hurricane Dorian disengaged after days of devastating terror parked over the Bahamas, destroying nearly everything it touched, with winds of over 185 miles per hour, gusts over 200, and storm surges of 22 feet.
In theory Dorian should have been categorized as a Category 6 storm, except Saffir-Simpson does not admit to any storm more powerful than Category 5. Saffir-Simpson furthermore doesn't consider the breadth or width of storms, the radius of maximum winds, nor a hurricane center's actual motion across the planet, termed 'translation speed', nor the storm surges or amount of rains they bring. Neither does Saffir-Simpson attempt to combine effects into an overall rating of destructive potential.
Much therefor has been written about the inadequacies of Saffir-Simpson by the press, in the Washington Post, Forbes, Popular Science, as well as in many blogs Cliff Mass climate blog, the websites of national weather agencies, and independent scientific research organizations.
Shortly after Hurricane Dorian struck the Caribbean, a seemingly mild Tropical Storm Imelda hit the Houston Texas area with wind speeds that were essentially tame, while damages from the nearly 40 inches of rainfall were devastating.
Saffir-Simpson divides one factor, wind strength, into five levels, and uses this aspect alone to predict levels of physical damage. Roughly linear, it was adapted to offer predictions about the effects of high wind on human habitations, trees, large buildings and infrastructure such as electric power, water supplies, and roadways. It was devised during a time when hurricanes were rare, and high strength hurricanes even more so. During the 20th Century, fewer homes existed along the coasts, and with less robust home construction, residents had more to fear from damages caused by wind, than water.
With the coasts crowded now by better built homes (in the US anyways), many residents have come to believe that water is the primary cause of damages offered by tropical storms and hurricanes. I hope shortly to allay that bias.
Read this from the published version of Saffir-Simpson Scale by the National Weather Service:
Category One
Winds 74-95 mph Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days. Irene of 1999, Katrina of 2005, and several others were Category One hurricanes at landfall in South Florida.
Category Two
Winds 96-110 mph (83-95 kt or 154-177 km/hr). Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks. Frances of 2004 was a Category Two when it hit just north of Palm Beach County, along with at least 10 other hurricanes which have struck South Florida since 1894.
Category Three
Winds 111-129 mph. Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes. Unnamed hurricanes of 1909, 1910, 1929, 1933, 1945, and 1949 were all Category 3 storms when they struck South Florida, as were King of 1950, Betsy of 1965, Jeanne of 2004, and Irma of 2017.
Category Four
Winds 130-156 mph. Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months. The 1888, 1900, 1919, 1926 Great Miami, 1928 Lake Okeechobee/Palm Beach, 1947, Donna of 1960 made landfall in South Florida as Category Four hurricanes.
Category Five
Winds 157 mph or higher. Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months. The Keys Hurricane of 1935 and Andrew of 1992 made landfall in South Florida as Category Five hurricanes.
As wind speeds increase, fueled by a hotter earth, they ultimately become more lethal than flooding, particularly if a high strength storm strikes a major city. The Saffir-Simpson scale needs to be expanded. Nature is moving the goal posts, by edging up the destructive powers of wind.
Wind strength does correlate to a drop in barometric pressure at a hurricane's eye, and to storm surges but these are only part of the overall damage equation. Expanding an enhanced SS scale to Cat 6, 7, 8, or 9 will require the work of meteorologists, physicists, and structural engineers, analyzing the effects of sustained winds at velocities higher than 170 mph. To accomplish that task fairly, the effects of greater storm surges and rainfall must be combined and analyzed as well.
What really is required is a full-spectrum, artificially intelligent hurricane damage estimation model. Fortunately much good work has been done in this area, and in this short entry it's my pleasure to cite a paper by Stephanie F. Pilkington and Hussam N. Mahmoud, entitled "Real-time Application of the Multihazard Hurricane Impact Level Model for the Atlantic Basin".
This paper is but part of a movement towards overall damage prediction models that will hopefully be implemented going forward, with wind speed only one input into the overall damage assessment. This visual from their paper gives an idea of the complexity and variety of inputs. We have the data, we simply need to integrate it on a wider scale to enable accurate cyclone forecasting, and modeling of the impact of future events.
Computer models are entirely capable of estimating the effects of not only wind speed, but storm surge and rainfall, and also to correlate these factors with land elevation data, drainage basin contours, municipal water and power infrastructure along with the density of residential and commercial construction to predict damages customized for each population center at risk from a particular storm path.
For instance high wind speeds in glass and steel cities may become more of a hazard than storm surge, whereas surge and rainfall induced flooding might prove more deadly to areas populated by single and two floor residential homes.
Slow Translation Speeds of Recent Storms
One frightening aspect of the new types of storms are the slow translation speeds. Instead of having to endure 150 mph winds for just a few hours, as in the past, Dorian delivered steady 170 mph winds over the same area of the Bahamas for several days because the storm itself barely moved 1 mile per hour!
Realizing that the physics of atmospheric energy absorption and dissipation are not fully understood, I decided to extrapolate Saffir-Simpson to maximum sustained winds of 255 mph. This required an expansion of the wind-strength scale with four more levels, up to Category 9.
Please understand that the linear nature of Saffir-Simpson does not imply that hurricane energies are therefor increasing in linear fashion. On the contrary, hurricane wind energy increases proportional to the cube of wind speed:
Wind Power Density = ½ (air density) × (wind speed)³
In bluntest possible terms this means that the destructive increase of a wind from 100 to 110 mph is far greater than from 90 mph to 100 mph. The linear nature of Saffir-Simpson seems designed to supply a peaceful description of the threat of various sized storms, during an era when obtaining reliable wind speed measurements was difficult. The extrapolation below is not meant to terrify, but it is terrifying, because we now realize that such wind speeds are possible, and can only wonder what that would mean if they struck a densely populated region with high rise buildings.
Sustained Wind Speeds (mph)
Saffir Simpson Category (expanded)
The possibilities below are not inconceivable, considering the galloping rate at which our planet is warming:
Category 6
Winds 176 to 196 mph. A high percentage of masonry homes will suffer major damage. Most frame houses will be devastated. Large commercial buildings will lose large areas of glass, with major damage to roofs. Total damages will approach 50%.
Category 7
Winds 197 to 214 mph. Most thin wall masonry homes will suffer extreme damage. Large steel buildings will lose most of their glass coverings, and internal contents of many will be stripped out exposing the steel frameworks. All aerial power lines and elevated water tanks will be destroyed. Total damages may approach 80%
Category 8
Winds of 215 to 239 mph. Frame buildings even of hurricane-type construction will be eradicated. Most brick masonry buildings will collapse, shorter cement block buildings severely damaged. Tall steel frame buildings will lose all or most of their glass and interior contents and interior walls. Some will suffer permanent structural damage. A few will topple over completely. Very few structures will retain any fenestration at all. Total damages will approach 90%.
Category 9
Winds of 240 to 255. Few residential dwellings will avoid total eradication. Many if not most skyscrapers will topple completely, causing catastrophic damage to buildings nearby. If such a storm hit a major city directly, total damages and destruction could approach 95%.
City-Killer Storms
The physics of cyclone development are not halted by a numeric barrier. 255 mph winds are entirely possible, and not to include the possibility of 'city killer storms' seems almost foolish.
Passengers aboard Planet Earth must unite and cooperate to defeat global warming. Unless we do, the outdated Saffir-Simpson scale will enter the annals of climate denial. Category 6 is needed now, and Category 7 will likely have to be created to rate storms hitting the East Coast within a few years. Category 8 or 9 storms will eventually finish the surface destruction of a planet that may have warmed in a very short time by 5 degrees Celsius.
We're not just talking about catastrophic warming, but catastrophic warming at a phenomenally fast rate. The quicker we allow warming to occur, the more vicious the storms that will be thrust at us.
A diminished Gulf Stream means more Powerful Storms.
Climate change has wrought disturbances to oceanic currents, and in particular has slowed the flow of the Gulf Stream. The warming of the Arctic Seas have damaged the heat-exchange engine of cold arctic waters which habitually flowed deep in the Atlantic, replacing layers of warmer waters of the Gulf Stream that flowed north.
Cyclones are an Oceanic Cooling Mechanism
As arctic permafrost melts, and arctic soils warm due to the loss of reflective snow (albedo affect) warmer glacial meltwaters are flowing into the Arctic seas, transferring landmass heat to the ocean bottom. The temperature differential between arctic and tropical oceans is decreasing. The more this differential decreases occurs the slower hot oceanic waters cool themselves with cold drinks from waters of the north. In other words, the mid-deep oceans can't shed heat. The heat within them builds up.
This creates hotter more stagnant waters off the coasts of North America, Asia, and Europe, and a weakened Gulf Stream that no longer can divert giant storms away from the coasts.
Hurricane Season will extend into late Autumn, even Winter
As the oceanic 'bathtub' warms, the waters remain heated longer, with less ocean currents to mix and cool. Then as the North Atlantic moves into autumn, air temperatures cool rapidly compared with the sea. Hotter waters lying dormant in the Atlantic ocean beneath those layers of cooler air are the perfect incubation media for extremely powerful and slow moving hurricanes.
Miami, and the cities of coastal Florida dodged a bullet from Hurricane Dorian, but the lucky should not gloat that most hurricanes have turned before striking our continent. In the past many cyclones have spun back out to warmer waters, and when in the rarer instances they made landfall, they weakened substantially, limiting damages to rain and storm surges.
An age of Land-preferring Cyclones
We must not derive comfort from past hurricane behavior. It is entirely possible that summer-heated water-soaked landmasses such as Florida, Texas, or portions of the Atlantic Coast will absorb as much or more solar energy as the deep waters of the Atlantic, particularly after a blazing hot summer, and thus will offer a potent energy source to feed a land-preferring cyclone with the strength of Hurricane Dorian, or greater. As storms progressively deforest these areas, their vulnerability to high wind speeds increases, and so does the rate at which they absorb solar heat.
Earth can absorb much more heat than land, since it is denser, but it transfers that heat less easily. However, since the schedule of storms has increased, the landmasses are often just recovering from one storm when a second strikes, and the water soaked earth is a better heat source for the power hungry rotating storm center.
In other words, hurricanes of the future may prefer a detour over a heated land mass, and even park there gaining strength for several days.
There are No Known limits to Hurricane strength
A Hurricane by nature is a heat engine, transforming energy accumulated by ocean waters (or in the future, land masses) to the upper atmosphere. While there are theoretical limits to the speeds that hurricanes might achieve on a planet of our size, gravitation, and atmosphere, the steady destruction of forests (themselves cooling engines), combined with the paving of the earth's surface by roads and cities, and the renewed assault on the arctic snows by greenhouse warming, combined with a logarithmic increase in emissions from burning of forests in the Amazon, Congo and Western US, are greatly accelerating the worst case warming scenarios predicted just ten years ago.
In the year 2000, scientists feared that within 100 years. earth's average atmospheric temperature would warm by 2 degrees C. yet now admit this scenario will unfold within just a few years. Global warming advances at full gallop. Nature constructs slowly, but disintegrates quickly. Earth's climate is falling off of a cliff, into a hellishly hot inferno.
Unless we get to the source of the problem first. Every human on this planet is needed to labor and restore forests, prairies, and ocean ecosystems that have kept our planet manageably cool.
Soil layers must be restored. We think of the trunks of trees, of blades of grass, but by far the greatest destruction to Earth's biomass has been to it's soils. The soils of the Great Plains, in Kansas for example, have been decreased from 33 feet thick, to less than a few feet in some areas.
Forests have been decimated by egregious lumbering practices. Every one of us has been wasteful of wood, of paper, and plastic. We've made ourselves vulnerable to the sun's terrifying heat. It's a terrible we find ourselves in, clean up our ways and become expert earty gardeners in very short order, or face the alternative.
