The (Nuclear) Winter of Our Discontent

The specter of a nuclear conflagration looms in the tinderbox that is the Middle East and South Asia. While heads of state and military leaders game out every possible result, including the nightmarish worst-case scenarios, it's worth also contemplating the collateral ramifications of a nuclear conflict, including its potentially dramatic effects on the climate.

Those ramifications, after all, would affect all of us, perhaps irrevocably.

If a nuclear war were to break out in the Middle East or South Asia (or anywhere else, for that matter), the least of our short-term worries would be climate change. But, depending on the size and number of weapons used, as well as the specific targets hit, a nuclear conflict could seriously impact the global climate system, ushering in a period of dramatic global cooling.

Even limited regional nuclear exchanges — which are more likely now that the number of nuclear weapons states has increased — would have major implications for the climate system that would be similar to, although not as severe as, the “nuclear winter” scenarios popularized during the Cold War, according to the most recent studies.

In fact, modern climate simulations show that the climate system may be even more sensitive to a nuclear conflict than previously thought.

Mushroom cloud of the first hydrogen bomb test. Credit: Reuters.

One 2007 study found that smoke from 100 small nuclear weapons detonated in cities would affect the atmosphere more than major volcanic eruptions such as Mt. Pinatubo in 1991 or Mt. Tambora in 1815, and would last for a longer period as well. The eruption of Mt. Tambora famously led to the “Year Without a Summer” in 1816.

Alan Robock of Rutgers University and his colleagues investigated the climatic effects of a nuclear exchange between two countries, during which each country uses 50 Hiroshima-size (15 kiloton) nuclear weapons to attack each other’s most populated urban areas. The study found that the soot and other pollutants from the detonations and subsequent fires would be vaulted high into the stratosphere, where they would reflect incoming solar radiation and cool the climate for years.

Robock’s research has shown that a global average surface cooling of 1.25 degrees Celsius would follow a small-scale nuclear war, and a decade later the planet would still be 0.5 degrees C cooler than it otherwise would have been, with even more severe cooling occurring in North America and other land areas.

For perspective, a 0.5 degree C change in global temperature is as powerful an effect as nearly three quarters of all the global warming caused by 250 years of manmade greenhouse gas emissions. Cooling of this magnitude could have major implications for global food production, which would take a major hit not only from cooler temperatures but also from decreased precipitation.

According to Robock, impacts of this scale appear relatively close to what might occur in a nuclear war between Israel and a nuclear-armed Iran, neither of which is likely to possess superpower-sized nuclear arsenals during the next several years. (The size of Israel’s arsenal is unknown, and this again assumes that Iran develops nukes at all, let alone 50 of them.) This could also apply to other countries with modest but powerful nuclear arsenals, such as India and Pakistan.

The nuclear winter concept originated during the Cold War, when scientists were considering the climatic effects of tens of thousands of nuclear weapons detonated by the U.S. and Russia, part of the strategic doctrine of “mutually assured destruction.”

Studies showed that the fires ignited by massive, worldwide nuclear explosions would loft huge amounts of smoke into the upper atmosphere, thereby plunging the planet into the coldest temperatures since the peak of the last Ice Age 18,000 years ago.

A 2007 reexamination of the original nuclear winter studies — this time using modern simulations of the climate system — found that a huge nuclear exchange would cool global temperatures by as much as 8 degrees Celsius. As one of the studies reported, that would be “a climate change unprecedented in speed and amplitude in the history of the human race.” A nuclear weapons-induced cooldown of this magnitude would dramatically slash precipitation and lower crop yields, causing millions to starve to death.

The nuclear winter concept was so apocalyptic that it helped encourage American and Russian policymakers to cut their nuclear arsenals. Perhaps it will again influence world leaders.