Guided hurricanes

Predictions revisited and Climate Change: News and Comments

Guided hurricanes

When speculating four decades ago about the military uses of geophysics, Gordon J.F. MacDonald of UCLA contemplated the triggering of earthquakes or tsunamis, or melting polar ice with nuclear weapons. And he didn’t overlook the idea of steering hurricanes to ravage the enemy’s coasts. Reminding me of that prediction is a report now in press in Geophysical Research Letters, about how natural variations in the colour of the sea help to guide cyclones in the Pacific. A cyclone, remember, is a loosely used generic term that includes the major storms called hurricanes (Atlantic), typhoons (Pacific) or tropical cyclones (Indian Ocean and Australia).

Contributing to Unless Peace Comes, (1968), in a chapter entitled “How to Wreck the Environment”, MacDonald wrote:

… preliminary experiments have been carried out on the seeding of hurricanes. The dynamics of hurricanes and the mechanism by which energy is transferred from the ocean into the atmosphere supporting the hurricane are poorly understood. Yet various schemes for both dissipation and steering can be imagined. Although hurricanes originate in tropical regions, they can travel into temperate latitudes, as the residents of New England know only too well. A controlled hurricane could be used as a weapon to terrorize opponents over substantial parts of the populated world.

It is generally supposed that a hurricane draws most of its energy from the sea over which it passes. The necessary process of heat transfer depends on wave action which permits the air to come in contact with a volume of water. This interaction between the air and water also stirs the upper layers of the atmosphere and permits the hurricane to draw on a substantially larger reservoir of heat than just the warm surface water. There may be ways, using monomolecular films of materials like those developed for covering reservoirs to reduce evaporation, for decreasing the local interaction between sea and air and thus preventing the ocean from providing energy to the hurricane in an accelerated fashion. Such a procedure, coupled with selective seeding, might provide hurricane guidance mechanisms. At present we are a long way from having the basic data and understanding necessary to carry out such experiments; nevertheless, the long-term possibility of developing and applying such techniques under the cover of nature’s irregularities presents a disquieting prospect.

The idea of suppressing hurricanes by altering the sea surface appeared in a more benign prediction by Roger Revelle of the Scripps Institution of Oceanography. In New Scientist in 1964 he visualized a fleet of ships with smoke generators strewing “micron-sized particles of aluminium oxide” or “an organic salt of magnesium” over the Atlantic Ocean to reflect sunlight and deny the hurricanes their thermal nourishment.

But by the1970s political problems were emerging about controlling cyclones. As Alec Nisbett of BBC-TV and I reported in our blockbuster “The Weather Machine” (1974), an American typhoon-moderating project called Stormfury, using cloud seeding, was scheduled for the Philippines but abandoned after complaints from the Japanese, who rely on typhoons for a quarter of their rainfall. Similarly, suppression of Atlantic hurricanes could reduce Europe’s late-summer rainfall.

So what about natural influences on cyclone development, as described in the new report?

It’s by Anand Gnanadesikan and colleagues at NOAA’s Geophysical Fluid Dynamics Laboratory in Princeton and at MIT. The basic idea is simple: an abundance of micro-algae living near the ocean surface colours the sea green with their chlorophyll and increases the absorption of solar energy near the surface – so raising the sea surface temperature and promoting the origin, nurturing and guidance of major storms. The abstract reads:

Because ocean color alters the absorption of sunlight, it can produce changes in sea surface temperatures with further impacts on atmospheric circulation. These changes can project onto fields previously recognized to alter the distribution of tropical cyclones. If the North Pacific subtropical gyre contained no absorbing and scattering materials, the result would be to reduce subtropical cyclone activity in the subtropical Northwest Pacific by 2/3, while concentrating cyclone tracks along the equator. Predicting tropical cyclone activity using coupled models may thus require consideration of the details of how heat moves into the upper thermocline as well as biogeochemical cycling.

As compared with chlorophyll concentrations observed by satellites, the computer model set the chlorophyll to zero in parts of the North Pacific Subtropical Gyre — a persistent pattern of clockwise circulation. Along the Equator, major storm formation went up by about 20 %, but over the gyre and nearby the storm count decreased by 70 %. Here’s a chart of the results.

Computed changes in the tracks of major storms in the Northwest Pacific, with an assumed de-greening of the ocean there. More storms track into the South China Sea, but virtually none move into the East China Sea and there are many fewer landfalls in Japan and South China. Figure 3c in Gnanadesikan et al. -- see reference.

In a nutshell, micro-algae already guide hurricane-force storms in essentially the way MacDonald visualized for climatic warriors, by adjusting conditions at the sea surface.

A can of worms (or a vial of micro-algae)

The interdisciplinary cross-links here are mind-boggling. The biological input exposes a new realm of uncertainty in climate physics, with possibly intricate feedbacks.

Gnanadesikan et al. note effects of El Niño, so there may be a biological factor in the teleconnections whereby El Niño and La Niña influence the weather around the world, including the Asian monsoon

And a few years ago Michael Berhrenfeld of Oregon State University and his colleagues reported that the primary bioproductivity of the ocean goes down as the sea surface warms. Here’s a map.

Ocean productivity (NPP) between 1999 and 2004 varied inversely with changes in sea surface temperature (SST) over 74 % of the coloured region of permanently stratified oceans. Yellow, increase in SST, decrease in NPP. Light blue, decrease in SST, increase in NPP. Dark blue,decreases in SST and NPP. Fig. 3c in Behrenfeld et al.-- see reference

As this runs counter to the earlier story about micro-algae helping to warm the sea surface, other factors must be at work. Don’t forget palaeoclimatology, with the changing abundances of carbon dioxide in the atmosphere. The micro-algae draw down carbon dioxide but are limited in productivity by their need to combine sunshine with limited supplies of nutrients in the ocean, which are themselves climate dependent.

Wheels within wheels, for consideration another time.

References

MacDonald in N. Calder (ed.) Unless Peace Comes, pp. 167-183, Allan Lane, 1968

Revelle in N. Calder (ed.) The World in 1984, New Scientist series reprinted by Penguin, 1965

Stormfury in “The Weather Machine” produced by Alec Nisbett, written by Nigel Calder, BBC-TV and co-producers, 1974

Anand Gnanadesikan et al., “How ocean color can steer Pacific tropical cyclones”, Geophysical Research Letters, in press, 2010. A related AGU press release at http://www.agu.org/news/press/pr_archives/2010/2010-25.shtml

Michael J. Behrenfeld et al. “Climate-driven trends in contemporary ocean productivity,” Nature, Vol. 444, pp. 752-755, 2006

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