an updraft of about 1 m per second. After 10 hours, most of the
smoke reached an altitude of 11 km, putting it into the stratosphere.
CHILL IN THE AIR Although wildfires are a prodigious source of
small particles in the atmosphere, the largest suppliers of what scientists call natural aerosols are major volcanic eruptions. The sun-blocking effect of the minuscule bits of volcanic ash and droplets of
water and sulfuric acid can cool Earth’s climate significantly for
months or even a year or two. The aerosols are especially persistent
if they reach the stratosphere, where they waft above most weather
and therefore aren’t efficiently cleansed from the atmosphere.
Once the volcanic plumes spread at high altitude, they typically
prevent no more than 1 percent of the sun’s light from reaching
Earth’s surface (SN: 2/18/06, p. 110). But high-flying smoke and
soot in the aftermath of even a limited nuclear war—one with as
few as 100 Hiroshima-size bombs—would be much denser than
that and the materials would block the sun as effectively as the
thick clouds of a stormy day do, says Luke Oman, an environmental scientist at Rutgers University in New Brunswick, N. J. He and
his colleagues used computer models to simulate the effects of just
such a war between India and Pakistan.
If those bombs exploded over the most-populated areas of the
nations, more than 5 million metric tons of smoke and soot would
soar into the sky. Most of those particles would stay aloft for more
than 6 years, says Oman. On average, the temperature at Earth’s
surface would drop around 1.25°C for up to 3 years—about four
times the short-term cooling effect resulting from the 1991 eruption of Mount Pinatubo in the Philippines. After 10 years, the
global average temperature would still be 0.5°C below normal.
Those temperature decreases may seem no more than a slight
chill, but they’re substantial, says Alan Robock, also of Rutgers
University. Temperatures in the first few years after a 100-bomb
India-Pakistan war would be cooler than during a centuries-
long cold spell called the Little Ice Age, which ended during the
mid-1800s. Average global temperatures were at that time
between 0.6°C and 0.7°C below what they are today, and glaciers advanced in mountainous regions worldwide.
While temperatures at Earth’s surface would drop, those in the
stratosphere would increase by 30°C or more for at least 3 years,
says Michael J. Mills, an atmospheric scientist at the University of
Colorado at Boulder. At those higher temperatures, the large quantities of nitrogen oxides formed during the nuclear explosions—
when nitrogen in the air literally burns—would destroy high-altitude ozone at rates much higher than
normal, he notes.
“Only
disarmament
can prevent
the possibility
of a nuclear
environmental
catastrophe.”
— ALAN ROBOCK,
RUTGERS UNIVERSITY
In the team’s simulations, between
50 and 70 percent of the ozone high
over polar regions disappeared. Losses
were lower over the tropics, but ozone
there still decreased by at least 10 percent. A 100-bomb nuclear exchange
would create “a global ozone hole,” says
Mills. Because animals are adapted to
the particular level of ozone protection
that’s normal for their latitudes, any
significant ozone loss could be catastrophic, he suggests.
“Only disarmament can prevent the
possibility of a nuclear environmental catastrophe,” Robock grimly
told the audience at the San Francisco meeting.
That a nuclear winter could be triggered by a regional war is
particularly ironic, adds Stephen Schneider, a climate scientist
at Stanford University. A few decades ago, people were afraid
that an all-out nuclear war between superpowers would trigger
a climate catastrophe. Today, the United States and Russia could
simply end up as helpless bystanders—who would nevertheless
be left out in the cold. ■
