There are nine nuclear-armed states in the world and nearly all of them continued with intensive nuclear modernization programs in 2024, upgrading existing weapons and adding newer versions.
That is one of the key findings of the Stockholm International Peace Research Institute’s (SIPRI) Yearbook 2025, an annual assessment of the state of armaments, disarmament and international security.
In the mid-1980s, nuclear warheads, bombs and shells worldwide numbered around 64,000. Today, the figure stands at an estimated 12,241. That trend now looks set to be reversed, according to the latest assessment.
“The most worrying single thing that we see in the nuclear arsenals at the moment is that the long-term reduction in the numbers of nuclear warheads is coming to an end,” SIPRI Director Dan Smith told DW.
The end of post-Cold War nuclear disarmament
Since the collapse of the Soviet Union in 1991 and the end of the Cold War, the dismantling of retired warheads — warheads removed from the nuclear stockpile — has outpaced the deployment of new ones.
While it is common practice for nuclear-armed states to modernize and upgrade their nuclear capabilities, Smith says there has been an intensification of this process since late in former US President Barack Obama’s final term, with more investment in new generations of missiles and carriers.
“Already for several years before then, the security horizon worldwide had been darkening and the nuclear-armed states were already starting to introduce these processes of what we would call this ‘intense’ process of modernization, so not just a little bit of tinkering, but some real steep changes,” Smith said.
SIPRI researchers conclude that of the world’s estimated 12,241 nuclear warheads in January 2025, about 9,614 were in military stockpiles: either placed on missiles or located on bases with operational forces, or in central storage that could potentially be deployed.
An estimated 3,912 of those warheads were deployed with missiles and aircraft, with around 2,100 of those kept in a state of high operational alert on ballistic missiles. Nearly all of those belonged to Russia or the US, but China may also now keep some warheads on missiles, according to the assessment.
Among the world’s nuclear-armed states — the United States, Russia, the United Kingdom, France, China, India, Pakistan, North Korea and Israel — Russia and the US possess 90% of all nuclear weapons.
SIPRI analysts now warn that more and more states are considering developing or hosting nuclear weapons, with revitalized national debates about nuclear status and strategy.
This includes new nuclear sharing arrangements: Russia claims to have deployed nuclear weapons on Belarusian territory, while several European NATO member states have signaled willingness to host US nuclear weapons.
International security deteriorating for over a decade
In 2007, Russian President Vladimir Putin delivered a speech at the Munich Security Conference in which he railed against the US-dominated world order, NATO’s eastward expansion and disarmament.
But just two years later in 2009, Obama announced the goal of total nuclear disarmament in Prague, the capital of the Czech Republic. “The existence of thousands of nuclear weapons is the most dangerous legacy of the Cold War,” he said.
He went on to say that the US would “take concrete steps towards a world without nuclear weapons” and negotiate a new Strategic Arms Reduction Treaty (New START) with Russia. That treaty was signed, and came into force in 2011.
But in the wake of Russia’s full-scale invasion of Ukraine in February 2022, the Biden administration published its 2022 Nuclear Posture Review which identified the modernization of the US nuclear arsenal as a top priority.
In February 2023, Russian President Vladimir Putin signed a bill halting Russia’s participation in the New START treaty.
“The tide of insecurity has been building slowly since 2007-08, through 2014, onto this moment when the waves start crashing down in February 2022,” Smith said. “I think that is when maybe many ordinary citizens woke up to this deterioration which was more than a decade old by that time.”
The bottom line is: the world’s nuclear arsenals are being enlarged and upgraded. SIPRI estimates that China now has at least 600 nuclear warheads and that its nuclear arsenal is growing faster than any other country’s.
India is also believed to have slightly expanded its nuclear arsenal in 2024, while Pakistan continued to develop new delivery systems and accumulate fissile material — a key component of nuclear weapons.
Israel, which on June 13 launched strikes targeting Iranian nuclear facilities, killing military leaders and nuclear scientists, maintains a policy of deliberate ambiguity over its own nuclear capabilities. However, it is believed to be in the process of modernizing its own nuclear arsenal, as well as upgrading a plutonium production reactor site in the Negev desert.
AI and space technologies up the threat of nuclear war
In his introduction to the SIPRI Yearbook 2025, Smith warns of the prospect of a new nuclear arms race that carries “much more risk and uncertainty” than during the Cold War era — largely due to the rise of artificial intelligence and new technologies in the fields of cyber capabilities and space assets.
“The coming nuclear arms race is going to be as much about AI, cyberspace and outer space as it is about missiles in bunkers or on submarines or bombs on aircrafts. It’s going to be as much about the software as about the hardware,” Smith said.
This complicates the question of how to control and monitor nuclear weapons and stockpiles when the competition between nuclear-armed states used to be more or less about numbers.
There are long-term discussions about AI in relation to what are commonly called “killer robots” (Lethal Autonomous Weapons Systems), and the use of automated and semi-automated drones since Russia’s full-scale invasion of Ukraine — but not so much in relation to nuclear weapons.
Artificial intelligence allows for a large amount of information to be processed extremely quickly and in theory this should help decision makers to react more quickly. However, if something goes wrong within the software or a system totally reliant on LLMs, machine learning and AI, a small technical glitch could potentially lead to a nuclear strike.
“I think there has to be a red line that probably all political leaders and military leaders will also agree with, that the decision on nuclear launch cannot be made by artificial intelligence,” Smith said, pointing to the example of Soviet Lieutenant Colonel Stanislav Petrov.
In 1983, Petrov was on duty at the Soviet nuclear early-warning system command center 62 miles south of Moscow when the system reported the launch of an intercontinental ballistic missile from the US, with four more behind it.
Luckily, Petrov suspected the warning was a false alarm and waited instead of relaying the information immediately up the chain of command — a decision which likely prevented a retaliatory nuclear strike, and in the worst-case scenario, full-scale nuclear war.
“I suppose the big question is that in a world of artificial intelligence, who plays the part of Lieutenant Colonel Petrov?” Smith asked.
