For four years, the United States was the only nation armed with nuclear weapons, until the Soviet Union tested a fission-based bomb in 1949. Following this, the United States developed weapons, called “thermonuclear” or “hydrogen” bombs, based on nuclear fusion, first tested over Eniwetok atoll in the mid-Pacific in 1954. Later tests by the United States and the Soviet Union, which detonated a thermonuclear weapon test at a Siberian site less than a year later, demonstrated that the new bombs could produce an explosive force equivalent to 20 megatons, 1,000 times greater than the bombs detonated at the Trinity site and over Hiroshima and Nagasaki (Forrow and Sidel 1998).

Medical Consequences

Concerned about the potential effects of thermonuclear weapons if used over a populated area, a group in Boston calling itself “Physicians for Social Responsibility” (PSR) examined the medical consequences of a possible attack. The Joint Congressional Committee on Atomic Energy had published in 1959 a description of a “limited” 1,446- megaton nuclear attack on missile bases and urban-industrial complexes in the United States, which it considered a “realistic possibility”(Nathan et al. 1962; Sidel et al. 1962).

The group predicted that severe traumatic injuries and massive burns, combined with radiation exposure, would kill over 1 million people and injure almost 1.5 million others in the Boston metropolitan area. With widespread destruction of medical care facilities, approximately 1 million of those injured would die. The responses by health professionals after nuclear weapons had exploded would be almost entirely futile and civil defense work would offer little benefit.

PSR asserted that physicians, because of their knowledge of the medical effects of these weapons and their responsibility to protect the health of their patients and their communities, had a special role to help prevent the use of nuclear weapons. The editor of the New England Journal of Medicine, in which the papers were published, agreed with this assessment (Garland 1962).

Given the distribution of the energy of thermonuclear weapons as blast (50%), heat (35%), initial radiation (10%), and fallout radiation (5%), their medical effects are summarized in Table 1. Although chemical, biological, and radioactive weapons are often grouped together with nuclear weapons as “weapons of mass destruction,” the magnitude of the adverse consequences of nuclear weapons is orders of magnitude greater than the impact of other types of weapons in this category.

Table 1. Medical Consequences of Thermonuclear Weapons

Current Arsenals

Britain (in 1952), France (in 1960), and China (in 1964) conducted successful tests of nuclear weapons in the two decades that followed their first use. India and Pakistan both tested nuclear weapons in 1998 and Israel is widely believed to have nuclear weapons, but has never acknowledged it publicly. North Korea may have a very small number of weapons and Iran, after attempts to develop nuclear weapons, denies it has current plans to develop them. South Africa destroyed its six nuclear weapons in 1991, when it appeared that a majority government was about to be elected.

There are approximately 23,000 nuclear warheads worldwide, with an equivalent explosive force of over 200,000 Hiroshima-sized bombs (Table 2). This is equivalent to at least 4 billion tons (4,000 megatons) of TNT. Thousands of these warheads are on “hair-trigger” alert, ready to be launched with a few minutes’ notice (Sutton and Gould 2008).

Table 2. Nuclear Stockpiles

(Source: Federation of American Scientists: Status of world nuclear forces, October 2009)

The total number of nuclear weapons may increase as other countries develop or acquire nuclear weapons. There is also the risk of non-state actors obtaining some of these weapons or the fissile material necessary to produce them.

“Nuclear Winter”

Use of nuclear weapons could cause cooling of the earth’s surface by clouds of soot and dust produced by the explosions, leading to severe food shortages. This claim, first made by Carl Sagan and colleagues in 1983 (Turco et al. 1983), is controversial, but recent analysis published in the Journal of Geophysical Research in 2007, based on current climate models, support the claim. Even detonation of a few weapons could lead to protracted and widespread cooling with widespread famine (Helfand, 2008; Mills et al., 2008).

Attempts to Limit Proliferation and to Ban Use of the Weapons

Nuclear Test Ban Treaties: In 1963, international concern over radioactive fallout from atmospheric nuclear tests led to the negotiation of a Partial Test Ban Treaty (PTBT), which banned nuclear tests in the atmosphere, under water, and in space. In 1996, a Comprehensive Test Ban Treaty (CTBT) was adopted by the General Assembly of the United Nations by more than two-thirds of its members. One hundred and fifty nations have now ratified the CTBT and another 32 have signed, but not yet ratified, it. The treaty would enter into force 180 days after the 44 states listed in its Annex 2 have ratified it; nine Annex 2 states have not yet ratified it. China, Egypt, Indonesia, Iran, Israel, and the United States have signed the CTBT, but India, North Korea, and Pakistan have not.

The Nuclear Non-Proliferation Treaty: The Nuclear Non-Proliferation Treaty (NPT) was opened for signature in 1968. There are 189 countries that have signed it, including five that have nuclear weapons: the United States, Russia, the United Kingdom, China, and France. However, India, Israel, North Korea, and Pakistan have not signed it. The NPT includes obligations requiring non-proliferation and disarmament, and the right to peacefully use nuclear technology. The treaty is reviewed every five years by the countries that have signed it.

A Nuclear Weapons Convention: Since 1996, the United Nations General Assembly has annually adopted a resolution calling on all countries to immediately fulfill their obligation, as articulated in an advisory opinion of the International Court of Justice, "by commencing multilateral negotiations leading to an early conclusion of a nuclear weapons convention." In 1997, a consortium of experts in law, science, disarmament, and negotiation drafted a model nuclear weapons convention, which Costa Rica submitted to the United Nations Secretary-General as a discussion draft.

This model convention would require countries with nuclear weapons to destroy them in stages, including (a) taking them off high-alert status, (b) removing them from deployment, (c) removing warheads from delivery vehicles, (d) disabling warheads by removing their explosive "pits", and (e) placing fissile material under the control of the United Nations. In addition to outlawing nuclear weapons, the convention would prohibit the production of fissile materials -- highly-enriched uranium or separated plutonium -- necessary for making them.

This model convention would establish an agency to ensure that countries comply with its terms. This agency would receive progress reports from nuclear-weapons states, conduct inspections of nuclear-weapons facilities, acquire intelligence through satellite imaging and remote sensing, and monitor production and transfer of materials necessary for making nuclear weapons.

Abolition of Nuclear Weapons

Increasingly, political leaders, diplomats, military officials, physicians, scientists, public health experts, and others are recognizing the need for the abolition of nuclear weapons. A letter to the Wall Street Journal, signed by George Shultz, William Perry, Henry Kissinger, and Sam Nunn, called for "a world free of nuclear weapons" (Shultz et al. 2007). The award of the Nobel Peace Prize to President Barack Obama in 2009, for “his extraordinary efforts to strengthen international diplomacy and cooperation,” and especially for his “vision of and work for a world without nuclear weapons,” offers hope for abolition. The future of humankind may depend on the elimination of these weapons.

Challenges Facing World Leaders

At the world waits for agreements to abolish nuclear weapons, leaders of nuclear weapons states and other countries face serious challenges to control of these weapons. These include: (1) preventing the spread of nuclear weapons to countries that do not currently possess them; (2) assuring the safety and security of nuclear warheads in nuclear-weapons states, most notably in Pakistan and Korea; (3) taking operational warheads off “hair-trigger” alert; (4) establishing a “no first use” policy and ensuring that a nuclear weapon is not detonated during a crisis situation; (5) resisting plans to increase or modernize current stockpiles; (6) building trust and cooperation among nuclear-weapons states as countries move toward nuclear weapons disarmament; and (7) and preventing terrorist organizations and religious extremists from obtaining nuclear weapons.