Federation of American Scientists Researchers Contribute Nuclear Weapons Expertise to International SIPRI Yearbook, Out Today
The Stockholm International Peace Research Institute (SIPRI) launches its annual assessment of the state of armaments, disarmament and international security
Washington, D.C. – June 16, 2025 – Nuclear weapons researchers at the Federation of American Scientists (FAS) contributed to the Stockholm International Peace Research Institute (SIPRI)’s annual Yearbook, released today. Key findings of SIPRI Yearbook 2025 are that a dangerous new nuclear arms race is emerging at a time when arms control regimes are severely weakened.
“The era of reductions in the number of nuclear weapons in the world, which had lasted since the end of the cold war, is coming to an end,” said Hans M. Kristensen, Associate Senior Fellow with SIPRI’s Weapons of Mass Destruction Programme and Director of the Nuclear Information Project at the Federation of American Scientists (FAS). “Instead, we see a clear trend of growing nuclear arsenals, sharpened nuclear rhetoric and the abandonment of arms control agreements.”
World’s nuclear arsenals being enlarged and upgraded
Nearly all of the nine nuclear-armed states—the United States, Russia, the United Kingdom, France, China, India, Pakistan, the Democratic People’s Republic of Korea (North Korea) and Israel—continued intensive nuclear modernization programmes in 2024, upgrading existing weapons and adding newer versions.
Of the total global inventory of an estimated 12,241 warheads in January 2025, about 9614 were in military stockpiles for potential use (see the table below). An estimated 3912 of those warheads were deployed with missiles and aircraft and the rest were in central storage. Around 2100 of the deployed warheads were kept in a state of high operational alert on ballistic missiles. Nearly all of these warheads belonged to Russia or the USA, but China may now keep some warheads on missiles during peacetime.
Since the end of the cold war, the gradual dismantlement of retired warheads by Russia and the USA has normally outstripped the deployment of new warheads, resulting in an overall year-on year decrease in the global inventory of nuclear weapons. This trend is likely to be reversed in the coming years, as the pace of dismantlement is slowing, while the deployment of new nuclear weapons is accelerating.
Russia and the USA together possess around 90 per cent of all nuclear weapons. The sizes of their respective military stockpiles (i.e. useable warheads) seem to have stayed relatively stable in 2024 but both states are implementing extensive modernization programmes that could increase the size and diversity of their arsenals in the future. If no new agreement is reached to cap their stockpiles, the number of warheads they deploy on strategic missiles seems likely to increase after the bilateral 2010 Treaty on Measures for the Further Reduction and Limitation of Strategic Offensive Arms (New START) expires in February 2026.
The USA’s comprehensive nuclear modernization programme is progressing but in 2024 faced planning and funding challenges that could delay and significantly increase the cost of the new strategic arsenal. Moreover, the addition of new non-strategic nuclear weapons to the US arsenal will place further stress on the modernization programme.
Russia’s nuclear modernization programme is also facing challenges that in 2024 included a test failure and the further delay of the new Sarmat intercontinental ballistic missile (ICBM) and slower than expected upgrades of other systems. Furthermore, an increase in Russia’s non-strategic nuclear warheads predicted by the USA in 2020 has so far not materialized.
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The Federation of American Scientists (FAS) works to advance progress on a broad suite of contemporary issues where science, technology, and innovation policy can deliver transformative impact, and seeks to ensure that scientific and technical expertise have a seat at the policymaking table. Established in 1945 by scientists in response to the atomic bomb, FAS continues to bring scientific rigor and analysis to address contemporary challenges. More information about FAS work at fas.org.
“The era of reductions in the number of nuclear weapons in the world, which had lasted since the end of the cold war, is coming to an end”
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Russia currently maintains nearly 5,460 nuclear warheads, with an estimated 1,718 deployed. This represents a slight decrease in total warheads from previous years but still positions Russia as the world’s largest nuclear power alongside the United States.
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