The devastating climate effects of even a small nuclear war

The continent-hopping doesn't seem to stop for me. Am in San Francisco at the moment, covering the American Geophysical Union's Fall meeting. These Americans know how to work a man hard, so no time for any major sightseeing yet (though I did go out to Monterey Bay on sunday and got a stunning view of the surf).

An interesting story from the first day of the meeting concerning the climate effects of a small-scale nuclear war. The researchers say that less than 100 Hiroshima-sized blasts would have devastating long-term effects on the climate. Crops would be out of action for five years, average temperature around the world would crash for ten years and the ozone layer would be decimated.

It's sobering given the seeming indifference to nuclear proliferation these days from major governments. India has just signed a deal with the US, for example, to share nuclear technology, ostensibly for its civilian programme. Both countries have hailed it as a major diplomatic breakthrough. There were reports that George Bush said recently that small-scale nuclear weapons could justifiably have been used to quell unrest in Iraq if necessary.

The American scientists behind the report argue that smaller conflicts are far more likely now than any major armageddon-type event (using 1000s of warheads) between the US and the Soviet Union was in the 1980s. They add that a confluence of three factors makes now the most dangerous time in history for human civilisation: increased nuclear proliferation; the migration of human populations into megacities and increased political instability.

Ther papers modelling the effects on climate and the one on human impacts are both available for discussion online.

Nuclear weapons pose the single biggest threat to the Earth's environment, scientists have warned.

In a new study of the potential global impacts of nuclear blasts, an American team found even a small-scale war would quickly devastate the world's climate and ecosystems, causing damage that would last for more than a decade.


Speaking at the American Geophysical Union's meeting in San Francisco yesterday, Richard Turco of UCLA said detonating between 50 and 100 bombs - just 0.03% of the world's arsenal - would throw enough soot into the atmosphere to create climactic anomalies unprecedented in human history.

Article continues
He said the effects would be "much greater than what we're talking about with global warming and anything that's happened in history with regards volcanic eruptions".

According to the research, tens of millions of people would die, global temperatures would crash and most of the world would be unable to grow crops for more than five years after a conflict.

In addition, the ozone layer, which protects the surface of the Earth from harmful ultraviolet radiation, would be depleted by 40% over many inhabited areas and up to 70% at the poles.

Alan Robock, the co-author of the study, told Guardian Unlimited: "Nuclear weapons are the greatest environmental danger to the planet from humans, not global warming or ozone depletion."

There are around 30,000 nuclear warheads worldwide, 95% of which are held by the US and Russia.

In addition, there is enough unrefined nuclear material to make a further 100,000 weapons.

Human costs
It was Prof Turco who coined the phrase "nuclear winter" in the 1980s to describe the potential apocalyptic global consequence of all-out nuclear war.

In this study he and Prof Robock led research teams to create models of the impacts from nuclear blasts.

They examined an exchange of 100 Hiroshima-sized nuclear bombs (15 kilotons each) between two countries, a conflict they argued was well within the ability of many emerging nuclear states.

The results showed that the most densely packed countries would fare worst in the aftermath of a nuclear war. India and Pakistan could face 12m and 9m immediate deaths respectively, while an attack on the UK would cause almost 3m immediate deaths.

A single nuclear blast in a major urban area would kill more than 125,000 people in the UK, injuring a further 100,000.

"Most of the human population is moving into very concentrated cities. At the same time, nuclear proliferation is accelerating again: we have Pakistan and India, Iran and North Korea," said Profe Turco.

While human losses would be constrained by geography, the environmental impacts of the bombs would spread worldwide.

Black smoke
In the 100 warhead scenario, more than 5m tonnes of sooty black smoke would spew from the resulting firestorms. This smoke would float to the upper atmosphere, get heated by the sun and end up being carried around the world.

The particles would absorb sunlight, preventing it from reaching the surface, which would result in a rapid cooling of the Earth by an average of 1.25C.

"This would be colder than the little ice age, the largest climate change in human history," said Prof Robock.

The model also showed that the smoke would stay in the upper atmosphere far longer than anyone had previously thought.

Older models had assumed that the smoke would linger for around a year, as has been observed with the dust from volcanic eruptions. However, using improved atmospheric data the new study showed that the climate would still be suffering a decade on from the initial conflict.

"Far removed from the conflict, there would be large impacts on agriculture - there would be less precipitation and less sunlight; it would be a huge shock to agriculture everywhere," said Prof Robock.

There is a precedent for this sort of climactic change: major volcanic eruptions in the past have thrown global ecosystems into temporary turmoil.

The eruption of Mount Tambora in 1815 was the biggest such event on record. The resulting cloud of ash spread around the world and caused crops to fail the following year in North America and Europe, resulting in the worst famine of the century.

Shock to the system
The scientists said a sudden change to the Earth's ecosystem because of nuclear blasts would be worse than any of the effects predicted by global warming due to greenhouse gases.

"Global warming is a problem and we certainly should address it but in 20 years, the temperature might go up by a few tenths of a degree and it will be gradual," said Prof Robock.

"We'll be able to adapt from some of it. But the climate change from even the small nuclear war we postulated would be instantaneous and such a shock to the system"

He said that the results should act as a warning to the international community.

"Proliferation is very dangerous - even using a couple of weapons is so much worse than anyone can imagine. I think the world should be much more concerned about proliferation than we are."

Prof Turco said that the end of the cold war had taken people's minds focus off the potential dangers of nuclear war.

"Look at 9/11 - there were 3,000 fatalities in that attack and that's considered a watershed in terms of terror that can be inflicted on a country. But in fact that's really a minor event to what's possible," he said.

"I can't imagine what would happen if there was a detonation in London: people would head to the countryside, there would be fallout everywhere, the country would shut down."