This spring I was stranded in Europe for a week, a minor victim of Mother Nature, as most airports on the continent were closed after the eruption of the Eyjafjallajökull volcano in Iceland. This remote natural event did not result in a huge human death toll but still caused hundreds of millions of dollars of lost revenue for almost all the world’s major airlines. More important, it disrupted millions of people’s lives.

Such is the nature of our modern interconnected society, where a catastrophe in one corner of the world can nonetheless affect almost immediately the livelihood and well-being of people around the globe.

The Icelandic eruption took on additional significance, following as it did the Nuclear Security Summit that President Barack Obama convened in Washington, D.C., to help begin to secure nuclear materials and to work toward combating global nuclear proliferation. For 40 years the world was focused on the possibility of mutually assured destruction and global annihilation, with literally thousands of nuclear weapons on hair-trigger alert, ready to be launched on the mere warning of an attack.

But the dangers facing the modern world are far more complex. The president has emphasized the devastating global economic and social impact that the explosion of even a single nuclear weapon in a major metropolis would have, beyond of course the tragic loss of human life. Moreover, as more countries in regions with rising geopolitical tensions seek to possess nuclear weapons, the likelihood of both nuclear terrorism and regional nuclear conflicts only continues to increase.

As the event in Iceland makes abundantly clear, “regional” is an illusion in the modern world. A recent set of scientific studies by Alan Robock of Rutgers University, Owen B. Toon of the University of Colorado at Boulder and their colleagues—reported on in journals ranging from Science to Scientific American (see the January 2010 issue)—demonstrates a more pernicious impact from even a limited nuclear exchange in what, for North Americans, would seem to be a remote part of the world where natural disasters might be more easily and habitually ignored.

The studies conclude that a regional nuclear conflict between India and Pakistan that detonated merely 100 Hiroshima-size weapons (which are far smaller than many of those in current nuclear arsenals) not only could produce as many fatalities as World War II but also would drastically disrupt the planet’s climate for at least a decade. Up to five million tons of smoke would rise above cloud level and within days form a global stratospheric smoke layer, which would for years block 7 to 10 percent of sunlight reaching the earth. Average surface temperatures could drop lower than they have at any time in the past millennium, significantly shortening growing seasons and reducing the average global precipitation.

To grasp the true magnitude of the human catastrophe from such a use of nuclear weapons, it is perhaps easiest to return to the situation in Europe after the Eyjafjallajökull eruption. Estimates I have gleaned from various sources suggest that the volcano spewed perhaps a million tons of particulate matter into the atmosphere, only slightly smaller in magnitude than the amount predicted to result from a limited nuclear weapons exchange. But the particles of soot from the intense fires ignited by nuclear explosions are much smaller and therefore rise higher into the atmosphere. They also reflect more light than the larger silicon particles emitted by volcanoes. The net result is that this soot would remain in the atmosphere far longer and have a much greater climate-changing effect, affecting agriculture worldwide.

A small volcano in Iceland that was able to paralyze commerce and travel for hundreds of millions of people around the world sends a chilling message: even a limited and remote use of nuclear weapons anywhere will be devastating on a global scale. Airline cancellations would be the least of our worries.