Black and white image taken from the air of a massive plume of smoke and a pyrocumulonimbus cloud over Earth’s surface
Fires ignited by the atomic bomb attack on Hiroshima, Japan, on 6 August 1945 pumped smoke and soot into the upper troposphere and lower stratosphere and created the pyrocumulonimbus cloud seen in this photo, which was taken more than 3 hours after the attack. Credit: U.S. Army

While we all recognize that global warming threatens humanity, the effects of nuclear war pose an even graver threat to the global population.

The immediate devastation from nuclear blasts and subsequent fires and the lasting harm from nuclear radiation have, of course, been demonstrated tragically. But a nuclear war would also produce nearly instantaneous climate change that among other effects, would threaten the global food supply. Even a regional nuclear war could threaten civilization globally and condemn innocent bystanders to famine, including inhabitants of the country that initiated the conflict. In effect, a nuclear attack would be the actions of a suicide bomber [Robock and Toon, 2012].

As nuclear arsenals and the plausibility of their use are growing anew, we argue that it is again time for physical scientists to advocate for steps that reduce the nuclear threat.

The scientific community, particularly physicists and geophysicists, has a special relationship with the problem of nuclear weapons. We have performed the research and developed the technology that created the weapons, and we have studied their effects. But there is also a long history of scientists opposing use of the weapons and warning of the outcomes in the event they are used. Today, as nuclear arsenals and the plausibility of their use are growing anew, we argue that it is again time for physical scientists to advocate for steps that reduce the nuclear threat. A new coalition is working to do just that.

The Growing Threat

The existence of nuclear weapons means that they can be used, and this threat is getting more severe as the number of possible scenarios leading to nuclear war rises. Currently, there are more than 9,000 nuclear warheads in the active military stockpiles of nine nations, with more than 90% of those in Russia and the United States. Nearly 2,000 warheads are on alert status, ready to launch within minutes of an order.

New technologies threaten the abilities of governments to control and secure nuclear weapons. A cyberattack on nuclear weapons control systems, for example, could create false warnings of launches or perhaps even initiate real launches. Even before the emergence of cyberthreats, there were many instances of near launches by technical or human error. And it was only because cooler heads prevailed that nuclear weapons were not used deliberately during the Cuban Missile Crisis in 1962 or amid the Vietnam War when military leaders urged their use [Ellsberg, 2017].

The nuclear arms control regime has been weakened in recent years with the termination of the Anti-Ballistic Missile Treaty and the Intermediate-Range Nuclear Forces Treaty between Russia and the United States, the withdrawals of those countries from the Treaty on Open Skies, and the withdrawal of the United States from the Iran nuclear deal. These actions are culminating in an emerging nuclear arms race, with most nuclear powers modernizing their nuclear arsenals. The planned trillion-dollar, multidecade modernization of the nuclear arsenal in the United States would commit the country to nuclear weapons for most of this century.

Nuclear Climate Change

In addition to immense physical damage to both built and natural environments, as well as lingering radioactive fallout, a nuclear conflict would cause rapid changes in Earth’s climate.

In addition to immense physical damage to both built and natural environments, as well as lingering radioactive fallout, a nuclear conflict would cause rapid changes in Earth’s climate. Smoke from firestorms ignited by attacks on cities and industrial areas would rise into the stratosphere and persist for years [e.g., Yu et al., 2019]. This smoke would block sunlight, causing global cooling [Robock et al., 2007a; Coupe et al., 2019], and it would lead to stratospheric ozone depletion that would enhance the amount of ultraviolet radiation reaching Earth’s surface [Bardeen et al., 2021].

The original suggestions of “nuclear winter” following a nuclear war by Turco et al. [1983] and Aleksandrov and Stenchikov [1983], which were based on very simple climate models, have been supported strongly by recent work using modern high-resolution general circulation models to simulate and predict its effects [Robock et al., 2007a; Coupe et al., 2019]. Even a regional nuclear war, such as between India and Pakistan [Robock et al., 2007b; Toon et al., 2019], in which less than 3% of the world’s nuclear weapons were detonated, would suddenly decrease the average global temperature by 1°C–7°C, precipitation by up to 40%, and sunlight by up to 30%. No matter the scale of the soot injection into the skies, the multiyear lifetime of smoke in the stratosphere means the effects on climate would last a decade, with the largest impacts continuing for more than 5 years. Such a conflict would decrease crop production to an extent that it could seriously threaten world food security and even trigger global famine [Jägermeyr et al., 2020; L. Xia et al., Global famine after nuclear war, submitted to Nature Food, 2021].

A Safer Path

There are many measures that can be implemented to reduce the likelihood of using nuclear weapons, including steps by the United States that in our view would make the country and the world safer. For example, we can adopt a no-first-use policy, meaning the United States would never start a nuclear war but, rather, only respond to a nuclear attack. We can also eliminate the launch-on-warning option, which pressures a presidential decision on whether to launch a counterattack within 5–10 minutes (and is thus particularly vulnerable to launches by error), and we can eliminate presidential sole authority to launch nuclear weapons. This most fateful decision should not be made by just one person [Perry and Collina, 2020]. In addition, we can and should restart the arms reduction negotiations between the United States and Russia that were initiated by President Ronald Reagan and Soviet leader Mikhail Gorbachev in the 1980s. These negotiations led to multidecade reductions in nuclear arsenals, but that progress has recently stalled.

We believe that the ultimate solution to the problem of nuclear weapons is to ban them globally. In 2017, the International Campaign to Abolish Nuclear Weapons led the effort to have the Treaty on the Prohibition of Nuclear Weapons signed at the United Nations. The campaign was awarded the 2017 Nobel Peace Prize “for its work to draw attention to the catastrophic humanitarian consequences of any use of nuclear weapons and for its ground-breaking efforts to achieve a treaty-based prohibition of such weapons.” The treaty came into force on 22 January 2021 after a 50th nation ratified it. Although the nuclear powers are not yet party to it, the treaty, which prohibits development, testing, possession, and use of nuclear weapons, nonetheless sets a new norm and direction for the future, much like existing treaties that prohibit the use of chemical weapons, biological weapons, land mines, and cluster bombs.

Physical scientists, including geoscientists, can offer expertise and insight into the hazards and consequences of nuclear conflict—and can be influential voices for nuclear threat reduction.

Because the “catastrophic humanitarian consequences” include not only the horrific direct effects but also potential impacts on climate and food supplies, physical scientists, including geoscientists, can offer expertise and insight into the hazards and consequences of nuclear conflict—and can be influential voices for nuclear threat reduction. In fact, at three international conferences, in 2013 and 2014, focused on the humanitarian impacts of nuclear war, participating climate scientists helped to push authorities from nonnuclear nations to sign and ratify the 2017 treaty.

Scientists have organized together in the past to exert pressure effectively on governments. Soon after physicists developed nuclear weapons in the 1940s, many then organized to warn of the dangers of nuclear arms. For example, James Franck and others published a report in June 1945 arguing against the use of a nuclear weapon in Japan; Albert Einstein led the Emergency Committee of Atomic Scientists, formed in 1946, to warn the public and mobilize scientists; and Niels Bohr urged world leaders, including Franklin Roosevelt and Winston Churchill, to preempt a postwar arms race. Through the Cold War, many scientists worked toward arms control and cooperative security. Geophysicists developed technologies to detect underground and atmospheric nuclear tests (sensors that as a by-product, have also been used to collect Earth observations). And in the mid-1980s, American and Russian climate scientists together warned Reagan and Gorbachev of the likely effects of a nuclear winter, helping to end the nuclear arms race. Recently, the U.S. physics community has again taken steps to influence U.S. nuclear policy—and geoscientists have the chance to join and work together with this community.

Influential Voices

In 2020, the American Physical Society (APS) initiated the Physicists Coalition for Nuclear Threat Reduction with the goal of creating a national network of physical scientists to advocate for nuclear threat reduction. A supporting goal is to inform the physical science community about nuclear arms issues. In its first year, the Physicists Coalition’s initial 13-member project team held more than 60 colloquia in physics departments and national laboratories around the country to provide an overview of the nuclear arms challenge and to introduce the community to the coalition. The program of colloquia is ongoing, and we continue to present webinars on specific arms control topics.

The coalition’s focus is now on advocating for the country to adopt a no-first-use policy, meaning its nuclear arsenal would remain only as a deterrent to attack.

Our advocacy work includes a broad array of actions but focuses on contacts and meetings with congressional representatives and staff. Throughout 2020, the coalition, along with other groups, successfully advocated to Congress not to approve a resumption of nuclear testing, which had been suggested by some legislators, and for the president to extend the New START Treaty, which limits the number of strategic nuclear weapons deployed by the United States and Russia. Soon after assuming the presidency, Joe Biden agreed with President Vladimir Putin to extend the treaty for 5 years. Now the coalition’s focus is on advocating for the country to adopt a no-first-use policy, meaning its nuclear arsenal would remain only as a deterrent to attack. Pulling the option of first use by the United States off the table can reduce geopolitical tensions that could lead to war.

The Physicists Coalition for Nuclear Threat Reduction welcomes all physical scientists, including those working in engineering science, to join, and we encourage you to host a colloquium, funded by the coalition, at your institution. The coalition offers an opportunity to be part of a movement specifically targeted at one of humanity’s most existential threats. We must solve the problem of nuclear weapons so that we have the luxury of devoting our time to solving the climate crisis.

Scientists can sign up to join the coalition and inquire about hosting a colloquium at For more information on nuclear arms and arms reduction efforts, join Alan Robock—virtually or in person—at the Stephen Schneider Lecture on 16 December during AGU’s Fall Meeting 2021.


Research on climate effects described here is supported by the Open Philanthropy Project. The authors are among the founding members of the Physicists Coalition for Nuclear Threat Reduction, which is supported by APS and the Carnegie Corporation of New York, partnered with APS Government Affairs, and managed through Princeton University’s Program on Science and Global Security. Opinions in this article represent those of the authors only.


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Author Information

Alan Robock (, Department of Environmental Sciences, Rutgers University, New Brunswick, N.J.; and Stewart C. Prager, Department of Astrophysical Sciences, Princeton University, Princeton, N.J.

Citation: Robock, A., and S. C. Prager (2021), Geoscientists can help reduce the threat of nuclear weapons, Eos, 102, Published on 2 December 2021.
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