New studies suggest that a small, regional nuclear conflict involving only a few weapons could have staggering global climate consequences, bringing about a 10-year-long cooling devastating to agriculture and society at large. Researchers have reported at a San Francisco scientific meeting that small warheads can pack a huge environmental punch if aimed at large population centers. VOA's David McAlary has details.

US nuclear test in Nevada

U.S. and Russian arms accords have led to a three-fold drop in the number of nuclear weapons since 1986. But the scientists who devised the concept of nuclear winter say the potential exists for numerous regional arms races. Eight nations are known to have nuclear weapons, two are building them, and 32 more have the plutonium or uranium needed for construction.

What if two of these countries attacked each other with nuclear arms? The scientists conducted computer simulations to find out and produced what they say is the first comprehensive look at the consequences of a conflict between small nuclear states.

"The results of these studies are quite surprising," said Owen Toon.

University of Colorado atmospheric scientist Owen Toon spoke at the American Geophysical Union meeting in San Francisco.

"Regional-scale nuclear conflicts can inflict casualties comparable to those once predicted for a strategic attack on the United States by the USSR, and that the smoke produced can endanger the entire population of Earth to climate changes and ozone loss," he said.

Toon and his colleagues say if low-yield nuclear weapons are aimed at the centers of major cities, they can produce 100 times more deaths and 100 times more smoke from firestorms per kiloton than big weapons. One outcome would be virtually a global ozone hole, the near total loss of the barrier that filters the sun's biologically harmful ultraviolet rays. The huge smoke cloud would occur because cities have far bigger supplies of fuel, plastics and other combustible materials, according to atmospheric scientist Richard Turco of the University of California at Los Angeles.

"It's remarkable that, owing to the confluence today of nuclear proliferation, migration into megacities, and centralization of economies within these cities, human society is extremely vulnerable at this point in time," said Richard Turco.

The researchers say a small nuclear war would probably occur in the tropics, not the higher latitudes as was once feared between Washington and Moscow. The studies show that tropical detonations would have harsher climate effects because the sun's heat could raise smoke from a firestorm higher into the atmosphere, where it would have a longer cooling effect on Earth.

Rutgers University environmental scientist Alan Robock says the potential impact could be long term and colder than the so-called Little Ice Age of the late middle ages when glaciers expanded and European rivers and canals froze during bitter winters.

"If this took place in 2006, you would have immediate large cooling and this would be a global climate change unprecedented in recorded history," noted Alan Robock.

Robock says the smoke emissions would block sunlight and lower temperatures by an average of more than one degree Celsius over large areas of North America and Eurasia, far beyond the nuclear explosions themselves.

"In areas far removed from where the smoke was put in, you would have reduction in the growing season by 10 to 30 days," he said. "There would also be effects on the reduction of precipitation and reductions of sunlight and disruption of society. The tropics would also have a huge reduction of temperature and it would be very difficult for agriculture."

The scientists say a small nuclear war would not lead to a nuclear winter of the kind that a superpower conflict could have produced, but it would be a substantial global disruption.

Again, Owen Toon of the University of Colorado.

"The current combination of nuclear proliferation, political instability, and urban demographics forms perhaps the greatest danger to the stability of society since the dawn of humanity," he said.