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Atlantic hurricane season officially stretches until the end of November, but the 2009 season seems to be over with barely a whimper.

The most interesting event of the hurricane season on this blog was our discussion on Aug. 22 (and several days following) about proposals to use cold water upwelling to potentially weaken hurricanes. Reporter Duncan Adams wrote an extensive article about such a proposal from The Egg Factory of Roanoke, filed in 2000.

The discussion veered from whether such a thing was technically possible to more a philosophical question of whether man should even attempt such a thing. The critics of the plan generally said that man shouldn't tamper with nature and that doing so could produce unintended bad consequences. Supporters favored the hurricane-weakening proposals as a way to save lives and property damage along our coasts.

A few of you asked me to give some thoughts, which I have in the Weather Journal column that appears Friday in The Roanoke Times.

In the extended entry below (click "Read More" in full blog mode) is a short e-mail interview I had with George Hagerman, the Egg Factory's hurricane expert, about the group's proposal and its potential effects.

Feel free to weigh in again with your own comments, whether you have before or not -- just keep it civil.

Question and answer by e-mail with George Hagerman, a senior research associate at Virginia Tech who serves as the ocean expert for The Egg Factory group proposing a method to reduce the strength of some hurricanes.

(1) The very big picture concern about hurricane modification is that a domino effect from any slight atmospheric changes ... like failure to transport enough atmospheric heat from the tropics to the temperature zones, a function of hurricanes ... can lead to additional subtle pattern shifts eventually adding up to major changes that could cause something (a drought, a heat wave, another tropical system, a non-tropical storm, etc.) to be more deadly or dangerous elsewhere. How do you address those concerns? 

Hagerman: Out of a dozen tropical cyclones that typically form in the Atlantic, Caribbean, and Gulf of Mexico each year, less than half will reach hurricane intensity, and at most, only one or two of these will threaten landfall near major population centers as major hurricanes (Category 3 or higher).  The Egg Factory invention is designed to simply reduce the intensity of these rare major hurricanes, not eliminate them.  So reducing the intensity of just one or two out of a dozen tropical cyclones each year should have little effect on the climate.

Moreover, extra-tropical storms (what we call “Nor’Easters” on the Virginia coast) – which occur in the late fall, winter, and spring – also transport large amounts of heat and moisture to the poles, probably in much greater amounts than tropical storms, due to the much larger size of these systems.  These would not be affected at all by the highly localized and temporary upwelling targeted at one or two hurricanes in the late summer or early fall.

 (1b) A very related concern is the fear that inland continental agricultural areas would be denied needed rainfall if hurricanes are overly modified. It is true that many times droughts have been broken by tropical systems, and that droughts have been worsened in some areas when tropical rainfall contribution is weak. How do you address those concerns?

Hagerman: See above.  Also, there are many factors besides intensity that affect the amount of rainfall delivered by a tropical storm or hurricane.

For example, Hurricane Agnes, in 1972, was barely a hurricane when it struck Florida.  It was only a tropical depression when it moved into the Northeast and combined with an extra-tropical low pressure system to produce an unprecedented amount of rainfall in the Mid-Atlantic states, ranging  from 6 to 19 inches from Virginia to New York.

 (2) What concerns about liability do you have? For instance, a hurricane develops, your technology is applied, but for some reason known or unknown, the hurricane doesn't weaken or even strengthens, and then devastates a coastal area. Do you think someone would try to hold the developer of the technology liable if it seemed to fail or didn't deliver what was expected?

Hagerman: In our litigious society, it certainly is possible.  One analogy that might be apt, is that when a fire company responds to a blaze and is unable to extinguish it before a building is declared a total loss (perhaps because the fire was simply too progressed, or the winds came up and fanned the flames), the fire company is not sued.

It has been demonstrated by well-validated meteorological models, and by the natural occurrence of hurricanes crossing cold-water wakes from previous storms, that they usually weaken – and that they never strengthen.

 (3) Do you think there is a chance that people will over-rely on the technology if it becomes widely applied? In other words, people won't take other precautions for an approaching hurricane because they put so much faith in modification, or they will not be ready in the case of a hurricane developing very close to shore rapidly when there might not be enough time to affect it substantially with upwelling?  (Hurricane Alicia in 1983, which rapidly went from a depression to Category 4 within short distance of the Texas coast, might be an example of this. Hurricane Humberto, which exploded from a disturbance to Category 2 inside of 24 hours last year before hitting the Texas/Louisiana border area, is a more recent example of what could happen very quickly a few miles from shore.)

Hagerman: The Egg Factory invention is NOT intended to be a replacement for effective forecasting of hurricane landfall, and the associated evacuation that should take place, regardless of the ultimate intensity of a landfalling storm. The purpose of this invention is to reduce the intensity of a major hurricane by one or – at most – two categories on the Saffir-Simpson scale, while it is still at sea and in relatively deep water (at least 500 m), so the “bubble subs” can stay submerged deeply enough that their carbon dioxide payloads remain in liquid form until they have converged beneath the core of the storm and can rise a few hundred meters, causing the CO2 to naturally “boil” and create upwelling bubble plumes.  Thus a Category 4 hurricane might be reduced to a Category 3 or Category 2 hurricane, which would still be a very dangerous storm.  The value of the Egg Factory’s proposed intensity reduction is that when the evacuees are able to return homes after the hurricane passes, they will still have largely intact homes and not be greeted by total devastation.

 (4) Warm sea surface temperatures are a concern related to global warming. Do you think your technology could have wider application in reducing sea surface temperatures in general? Also, on a more regional scale, could it be used pre-emptively, lowering sea-surface temperatures in especially hot areas even before a hurricane develops?

 Hagerman: The Egg Factory invention would not be cost-effective if deployed over a wide area to simply cool the surface, but it does not need be deployed over an grossly extreme wide area.   This is the essence of the invention using submersibles that are mobile and can track and target.  What makes this invention so practical is that guided by satellite hurricane tracking data, the submerged fleet of “bubble subs” would maneuver so as to concentrate beneath a portion of the hurricane eyewall, and then maneuver in the relatively calm waters beneath the thermocline to “stay with” the hurricane, continuing to bubble up cold water directly beneath its core.  The subs would aid the hurricanes own upwelling action to diminish its intensity.  Note the yellow highlighted passage from this recent blog entry at Weather Underground:

 http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1316:  Hurricane Fred continues its slow decline, as wind shear of 25 knots tilts and stretches the storm, allowing dry air to penetrate into the hurricane core from the southwest side. With sea surface temperatures down near the threshold needed to support a tropical cyclone and wind shear expected to increase to 30 knots Saturday, Fred should continue to weaken the next few days. The storm's very slow motion will hasten this decay, since the storm will stir up cold waters from the depths that it will not be able to move away from. Fred will likely die by Tuesday.

In essence, a fleet of Egg Factory “bubble subs” will act in the same way, so that even a fast-moving hurricane cannot get away from the upwelling cold water.

 The Egg Factory invention is specifically designed to reduce the intensity of a highly localized hurricane, as described in the above paragraphs, and not to tackle global climate change.  It is important to note, however, that because carbon dioxide (CO2) is used as the gas for creating the bubble plumes, a renewable energy resource must be used to produce the CO2, which would be done by liquefaction and distillation of air from the atmosphere, so that there would be no net increase in atmospheric CO2.

 Since CO2 can exist in a liquid state only at elevated pressures and cold temperatures, the Egg Factory invention can be more readily reduced to practice the production of liquid CO2 at sea, with storage and refueling of “bubble subs” at the same depth at which CO2 exists naturally as a liquid.  In the tropical ocean areas where mobile submerged fleets might be staged to intercept hurricanes, ocean thermal-gradient energy is an abundant, regionally available renewable energy resource for powering liquid CO2 production plants.

 Ocean thermal energy conversion (OTEC) is a renewable energy technology that has been proven at sea, with sufficient research and development already done to establish engineering feasibility at a scale appropriate to the power needs of a liquid CO2 production and submersible payload recharging platform. Thus the Egg Factory invention can be entirely ocean-based and self-sustaining in its requirements for energy and raw materials, with no net emission of atmospheric CO2.

 The OTEC resource is geographically distributed in a manner coincident with all global regions of tropical cyclone activity (see OTEC resource map at www.nrel.gov/otec/markets.html).

 Therefore, an important by-product of developing a cost-effective, sea-based OTEC system to power liquid CO2 production for recharging fleets of “bubble subs” is the accelerated commercial development of OTEC as a baseload power source that ultimately could replace coal-fired generation.  In this indirect way, The Egg Factory invention could lead to the substantial reduction of net CO2 emissions (and its attendant negative consequences, which include not only atmospheric and oceanic warming, but also ocean acidification) to the extent that fossil fuels can be replaced with OTEC-produced fuels such as ammonia.