Climatic Effects of Nuclear War

By Steven Starr, MT

Authoritative new studies from three US universities have concluded that virtually any nuclear war would gravely impact the global climate and environment. Scientists studied a range of nuclear wars; they found that 100 nuclear weapons, each the size of the one that destroyed Hiroshima, if detonated in a war between India and Pakistan, would seriously disrupt Earth's climate and destroy much of its protective ozone layer.

Larger conflicts fought with modern strategic nuclear weapons were also considered. The detonation of several thousand US and Russian nuclear weapons in urban areas were predicted to create extreme environmental devastation and Ice Age weather conditions lasting for more than a decade. This would eliminate growing seasons and create a nuclear famine which would kill most people on Earth.

Nuclear Darkness

How would this happen? Nuclear weapons are thousands to millions of times more powerful than conventional high-explosives and produce temperatures hotter than those found in the center of the sun.

The detonation of nuclear weapons in cities would ignite enormous mass fires. A Hiroshima-size bomb sets about 12 sq km on fire; an average Russian warhead would create a firestorm with a total surface are of about 225 sq km.

There are currently about 23,200 intact nuclear weapons in the global nuclear arsenals; the US and Russia own about 95% of these weapons. They keep about 7500 of them deployed and ready for immediate use.

About 2200 of these weapons are mounted on approximately 900 missiles which can be launched with only a few minutes warning. These are the high-alert nuclear weapons; they cannot be recalled once they are launched and require only 12 to 30 minutes to reach their targets (12 minutes for submarine launched missiles and 30 minutes for land-based intercontinental ballistic missiles) . See the table {below} for a comparison of the scale of the existing nuclear arsenal to conventional weapons and to the type of bomb used at Hiroshama.

Why are nuclear weapons kept on high alert? There is no defence against a massive first-strike attack by nuclear-tipped missiles, so the military solution was and is to launch them on warning before they are destroyed by the incoming attack. A false warning believed to be real could cause a retaliatory launch, thus resulting immediately in an accidental nuclear war (the retaliation could be launched on only the basis of electronic warning signals before the attack is confirmed by nuclear detonations).

And false warnings do occur -- because of human error, technical error, or potentially because of terrorist sabotage. For example, a terrorist group might introduce computer viruses or software into the systems of early warning or into the nuclear command-and-control systems, mimicking a full-scale nuclear attack.

How does nuclear war cause deadly climate change?

Millions of tons of smoke from hundreds or thousands of nuclear detonations would rise into the stratosphere, above cloud level, and quickly spread around the planet. A global smoke layer would form and block the warming sunlight from reaching the surface of the earth. Nuclear darkness would cause rapid drops in surface temperatures and create Ice Age weather conditions which would last for many years.

Hiroshima and Nagasaki were destroyed with "low-yield" nuclear weapons. Scientists estimate that a war which detonated 100 of these size weapons in the large cities of India and Pakistan would cause about 5 million tons of smoke to enter the stratosphere. This smoke would block about 10% of warming sunlight from reaching the surface of the Northern Hemisphere and produce the lowest average temperatures experienced there in the last 1,000 years.

The cold weather would significantly shorten growing seasons and reduce average precipitation. This would cause major grain shortages and lead to starvation for much of the world's already hungry populations.

The smoke would also destroy 25-45% of the Earth's protective ozone layer over the mid-latitudes and 60-70% over the northern high latitudes, vastly increasing the amount of harmful UV light reaching the surface of Earth. It is clear that this would have significantly harmful effects for all forms of animal and plant life; e.g., phytoplankton (which form the basis of marine ecosystems) are very sensitive to increases of UV light.

Nuclear war fought with high-yield nuclear weapons

What would be the consequences of a war with high-yield nuclear weapons? Scientists estimate that a US-Russian war, fought with 4400 strategic nuclear weapons (80% of the currently deployed US and Russian nuclear arsenals) could cause up to 180 million tons of smoke to enter the stratosphere. This would block 70% of the light from reaching the surface of the Northern Hemisphere and 35% of the light from reaching the surface of the Southern Hemisphere.

The Earth would become colder than it was 18,000 years ago. Minimum daily temperatures in the largest agricultural regions of the Northern Hemisphere would fall below freezing for one to three years. Growing seasons would be eliminated for a decade. Most people and large animals would starve to death.

The most lethal effects of nuclear war appear to be its predicted impact on global climate. The rapidity of that climate change makes it far more deadly than the expected climate change from global warming; there is no time for living things to adapt.

In addition to deadly climate change, there would be other toxic environmental effects. A large war would produce massive radioactive fallout, releasing a million times more radiation than did the accident at Chernobyl. If the bombs targeted nuclear reactors, this would increase the fallout by a factor of ten. Industrial chemicals (released by blast and fire) and ground-hugging clouds of toxic smoke would assault the ecosystems. There would be a massive decrease in stratospheric ozone, resulting in huge increases in harmful ultraviolet radiation.

The detonation of US and Russian nuclear weapons would leave the Earth uninhabitable. Even if the ongoing negotiations between the two countries result in the reduction of their nuclear weapons to just a few thousand, this will not significantly reduce this danger. The only way to insure that this outcome will not occur is by eliminating nuclear arsenals and abolishing nuclear weapons altogether.

What are the logical political solutions to this danger? High-alert nuclear weapons must be eliminated. The number of deployed nuclear warheads must be radically lowered. Tens of thousands of other nuclear weapons, which now remain in the reserve arsenals, must be dismantled. Finally, an international treaty must be adopted that eliminates nuclear weapons; the treaty can be similar to existing treaties that ban chemical and biological weapons.

A Treaty to Eliminate Nuclear Weapons

Such a draft treaty - a model nuclear weapons convention - has been submitted to the United Nations. It would prohibit the development, testing, production, stockpiling, transfer, use, and threat of use of nuclear weapons, as well as the production of fissile material suitable for making them (either highly enriched uranium or separated plutonium). It would require all nuclear-armed countries to destroy their nuclear weapons in stages. The last stage would place all fissile material under international control to prevent nuclear weapons ever being made again.

An agency would be created to verify compliance with the terms of the treaty. It would receive progress reports from nuclear-armed states; inspect weapons facilities, acquire data via satellite photography and remote sensors, and monitor the production and transfer of material suitable for making nuclear weapons. To see this model nuclear weapons convention, visit the ICAN website:

Steven Starr is the senior scientist for Physicians for Social Responsibility. See <> for detailed information on the nuclear climate issue.

Largest U.S. conventional bomb in 2009 = 11 tons TNT

Hiroshima-size nuclear weapon = 15,000 tons TNT

Smallest strategic nuclear weapon = 100,000 tons TNT

Large U.S. strategic nuclear weapon = 1,300,000 tons TNT

Largest known strategic nuclear weapon = 100,000,000 tons TNT

Peace Magazine Jul-Sep 2009

Peace Magazine Jul-Sep 2009, page 6. Some rights reserved.

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