This article is part of a series by the Green European Journal looking at the impacts of Russia’s war in Ukraine.

Following the 1991 referendum on Ukrainian independence, when 93 per cent voted to form their own state, the fledgling country briefly found itself in possession of the world’s third largest nuclear arsenal. Though lacking operational control of the weapons, Kyiv was wary to give them up, especially as some Russian politicians were threatening to annex Crimea. In 1994, Ukraine’s leaders agreed to send the nukes to Russia, joined the Nuclear Non-Proliferation Treaty, and signed the Budapest Agreement, in which Russia, the United States, and the United Kingdom pledged to never use force against Ukraine, to respect the country’s sovereignty and existing borders, and to assist if any country ever threatened it.

Moscow made a mockery of the agreement in 2014 when it annexed Crimea and sent its troops into eastern Ukraine to organise a violent secessionist uprising that resulted in 14,000 killed, and the US and UK did little to help. On February 24 of this year, president Vladimir Putin not only betrayed Russia’s pledge to Ukraine once again by launching a massive invasion, but threatened the world against trying to stop him by invoking nuclear weapons. “The consequences will be such as you have never seen in your entire history,” he sneered, boasting that Russia remains “one of the most powerful nuclear states,” with “a certain advantage in several cutting-edge weapons.” Three days later, Putin put his forces on a “special regime of alert,” though this apparently amounted only to a slight increase in personnel at military command centers.

Meanwhile, United Nations Secretary-General Antonio Guterres warned that “the prospect of nuclear conflict, once unthinkable, is now back within the realm of possibility,” as France deployed two additional nuclear missile submarines.

Adding to concerns, Russian diplomat to the United Nations Boris Bondarev denounced the war and warned the New York Times in May that his colleagues, some of whom work in arms control, talk openly about nuclear strikes against the West, assuming Western politicians would be too soft to respond in kind. “That’s how many of our people think, and I fear that this is the line that they are passing along to Moscow,” he said.

Russia’s nuclear doctrine

Though the risk of nuclear weapons is currently the highest it’s been in decades, Moscow is exceedingly unlikely to launch a nuclear weapon at any NATO country due to the near certainty of a nuclear response. Even in Ukraine, a Russian nuclear strike appears highly improbable at this point in Putin’s war, simply because it would serve little conceivable purpose on the battlefield.

Pavel Podvig, a leading expert on Russian nuclear weapons at the United Nations Institute for Disarmament Research, is doubtful that Moscow would break the nearly 80-year taboo against using nukes. “There are targets, but nothing [that] would require or justify using a nuclear weapon. There are no concentrations of troops or aircraft carrier groups that you would need nuclear weapons to attack,” he said.

Aaron Stein, a non-proliferation expert and the director of research at the Foreign Policy Research Institute (FPRI) in Philadelphia notes that Russian conventional forces have already been able to destroy an enormous number of Ukrainian targets, so there’s little need for nuclear weapons. “The Russians have destroyed basically all of Ukraine’s pretty robust domestic defence base with conventional precision guided munitions, so I just don’t know what use [nuclear weapons] have.”

Stein further warns against alarmism about a “nuclear madman”. Putin’s decision-making may be based on faulty information and not follow international norms, but that doesn’t make him irrational. The invasion of Ukraine was a disaster, but that’s likely because of faulty intelligence and poor military performance rather than any mental instability on Putin’s part. For him, the invasion was a perfectly rational move, with clear risks but potentially huge benefits. “It’s fallacy to suggest he’s irrational because we think his actions are irrational,” Stein explained. “We can’t extrapolate from our own conceptions of rationality that he’ll use nuclear weapons.”

Russian nuclear doctrine allows the use of nuclear weapons either in response to a nuclear attack on Russia or its allies, or in the case of an overwhelming conventional attack that would either threaten Russia’s nuclear forces, or which jeopardises “the very existence of the state.” In Stein’s view, “the Ukraine war doesn’t really meet any of these criteria.”

Stein warns against alarmism about a “nuclear madman”. Putin’s decision-making may be based on faulty information and not follow international norms, but that doesn’t make him irrational.

Will Putin cross the line?

Stein sees this war as playing out much like previous conflicts involving nuclear powers – there are clear red lines, and so long as those lines aren’t crossed, the risk of a nuclear strike is low. Russia’s red line is that NATO troops don’t directly intervene; NATO’s is that Russia doesn’t attack any of the alliance’s member states. Western countries supplying heavy weapons to Ukraine won’t likely provoke a nuclear response, and history bears this out.

During the Vietnam War, the Soviet Union sent massive amounts of heavy weapons and thousands of “military advisors” who operated anti-aircraft sites to shoot down American planes. In the Korean War, Soviet pilots flying Mig-15s downed large numbers of US aircraft, though this was hidden from both the American and Soviet publics at the time. The US also sent thousands of Stinger missiles to mujahideen rebels fighting Soviet troops in Afghanistan.

After a series of extraordinary battlefield successes in the early months of the current war, the Ukrainians in the eastern Donbas region are now being pounded with Russian artillery, which reaches much further than theirs. The Ukrainian defenders are reportedly outgunned by the Russians by at least 10-15 to one, and losing up to 200 soldiers per day, which has resulted in a deficit of trained men. Russia now occupies one-fifth of Ukraine.

For the time being, Moscow has scaled down its war aims to annexing the Donbas, and may very well prevail, which negates any potential need for nuclear weapons. “[The Russians] are quite possibly going to win, at least in their own minds, so there is no place for nuclear weapons,” Stein said.

However, the war remains highly fluid, with territory regularly shifting between sides. Russia, facing a manpower shortage because it refuses to admit the conflict is a war and fully mobilise, has suffered massive losses, and the Pentagon estimates Moscow has lost approximately 30 per cent of its armoured vehicles and used up 70 per cent of its precision-guided munitions. Western sanctions, which will further bite into the Russian war machine in the coming months, will make it very hard if not impossible to recover many of the losses of materiel. As one of the leading experts on Russian armed forces Michael Kofman has written, “even though the local military balance in the Donbas appears favourable to Russia, the overall trends in the military balance still favour Ukraine.”

Why deterrence fails in a fluid war

In the long run, the war could very well shift once again in Ukraine’s favour, assuming the West greatly increases its shipments of crucial heavy weapons in time. The most just outcome for Ukraine and for Europe is the decisive defeat of Russian forces within Ukraine. But herein lies the catch-22 to the nuclear threat: though still unlikely, if Russian forces stood on the verge of a decisive defeat, particularly if Crimea came under threat, this would be the most probable time that Putin could consider a nuclear strike.

“If it felt like Ukraine had decisively won the war and Russia was losing relatively to what it had in February, I think that’s one of the scenarios where it would be most likely,” said Nicholas Miller, an expert on nuclear proliferation and international security at Dartmouth College in New Hampshire who believes a nuclear strike is unlikely but troubling nonetheless.

Another concern is that, should Putin find himself in such a situation where he feels like a nuclear strike could be valuable, two traditional disincentives to use nuclear weapons may not apply. The first is deterrence – since Ukraine lacks nuclear weapons and NATO is very unlikely to respond in kind to a Russian nuclear strike in Ukraine, there is little deterrence against such a strike. “Putin might be able to tell himself a story about how he could use nuclear weapons in kind of a limited fashion and get away with it, or at least limit the costs he faces,” Miller said.

The second disincentive is the so-called “nuclear taboo” or “tradition of non-use” based on the belief that such weapons are uniquely reprehensible. After having destroyed entire large cities in Ukraine and elsewhere – Grozny, Aleppo, Mariupol – and having rewarded the unit reportedly responsible for the mass atrocities committed in Bucha, it seems dubious that Putin would have any moral qualms with using nuclear weapons if he felt an urgent need.

Though still unlikely, if Russian forces stood on the verge of a decisive defeat, particularly if Crimea came under threat, this would be the most probable time that Putin could consider a nuclear strike.

“I doubt that Putin has a moral reservation about using nuclear weapons, but he might still be restrained by these political and reputational consequences and the prospect of NATO maybe getting directly involved in the war,” said Miller, who points out that even leaders who haven’t internalised the nuclear taboo can be inhibited by potential negative consequences. A nuclear strike would surely result in stronger sanctions and international condemnation spreading beyond the Western world. “The big question is whether it would lead to NATO getting directly involved, and my guess is it would in some form,” Miller said, predicting that potential NATO involvement would possibly be limited to troops in western Ukraine or the use of airpower without boots on the ground.

Russia’s use of a nuclear weapon could also very well have the opposite effect and deter NATO from direct involvement, but Miller points out this would establish a dangerous precedent for nuclear coercion. “I think the US and most NATO countries would be very worried about the idea of setting a precedent where you can use nuclear weapons for that sort of coercive effect, and you could convince the West to back down by using a nuclear weapon in Ukraine.”

The lack of battlefield targets may not be much of an inhibitor either, since the use of nuclear weapons is at least as much about strategy and psychology as it is about tactics. “The only remotely plausible use of a nuclear weapon would be to use them strategically, to use them in a Hiroshima, Nagasaki kind of style, when you use them to kill a lot of people and break the will of an opponent to resist,” Podvig said, though he remains highly skeptical of such a use in Ukraine.

The politics of Putin’s nuclear blustering

“If [Putin] were going to use nuclear weapons, it would be less about the physical destruction of whatever target he was going after, and more about trying to send a political signal to Ukraine and to the West of the risk of further escalation if they don’t back down,” added Miller. “I think more likely, if he was going to do it, he’d use lower yield nuclear weapons against some sort of Ukrainian military or infrastructure target, and yes, it would cause destruction there and help the war effort, but I think the bigger effect would be trying to signal to Ukraine the risks of continuing to push forward against Russian forces.”

As for Russian nuclear doctrine, it can simply be ignored in a personalised regime such as Putin’s where one man commands near total control, but there’s also one part that’s dangerously vague and open to interpretation, threatening the use of weapons when the Russian state’s “existence” is under threat.

In his February 24 speech, Putin seemed to indicate the existential importance of this war: “For our country, it is a matter of life and death, a matter of our historical future as a nation…It is not only a very real threat to our interests but to the very existence of our state and to its sovereignty.”

“If he thinks there’s a decisive military defeat that could threaten his own grip on power, to him that might seem existential,” Miller said. Compared to previous nuclear powers facing defeat, such as the US in Vietnam or the Soviets in Afghanistan, Moscow regards the war in Ukraine as far more important, and a loss there may be seen as unacceptable. Putin has long been fixated on Ukraine, has for years reiterated that it’s not a ‘real’ country and that Russians and Ukrainians are one single nation, declaring in 2014 during the annexation of Crimea that “we cannot live without each other.”

To deter Putin from considering the nuclear option, Miller advises that the West make it loud and clear that the use of nuclear weapons is unacceptable and would result in severe consequences, as US president Joe Biden wrote in a recent op-ed. Podvig said the worst thing NATO could do is respond in kind with a nuclear strike, and should instead continue to reinforce the nuclear taboo. “To marginalise the thought of nuclear use, the United States and NATO should make it very clear publicly that they will not be using nuclear weapons in this conflict,” he said.

Putin has long been fixated on Ukraine, has for years reiterated that it’s not a ‘real’ country and that Russians and Ukrainians are one single nation.

For the time being, the risk of Putin resorting to nuclear weapons remains very low, but he is reportedly prepared for a very long war and is betting that western support for Ukraine will waver. In order to achieve the just outcome that Ukrainian and most western leaders have advocated for, the West needs to increase its heavy weapons supplies, particularly long-range artillery. Thus far, heavy weapons shipments have only amounted to a small percentage of what Kyiv requires.

Viola von Cramon, MEP for the Greens and Vice-Chair of the Delegation to the EU-Ukraine Parliamentary Association Committee, reiterates in an email to the Green European Journal that the Greens strongly support Ukraine’s territorial integrity and sovereignty. “It is up to [the Ukrainians] to decide when to [stop] defending themselves and when to sit at the negotiation table,” she wrote. “We need to continue supporting Ukraine with weapons that will help Kyiv to re-establish control of the occupied territories.”

Von Cramon warns that Putin’s nuclear blustering is aimed at dithering Western politicians. “Conceding to [Putin’s] blackmailing is very dangerous and opens a Pandora’s box where any nuclear state can extort any concession from the international community with impunity,” von Cramon wrote.

This is a valid point, and nuclear deterrence between Russia and NATO make a direct confrontation unlikely, but deterrence is never perfect, even when both sides want to avoid direct conflict. There is potential for escalation, for example, if Russia chooses to hit the very tempting target of weapons in Poland slated for Ukraine, or if Ukrainian forces use western long-range weapons to strike targets inside Russia. Moscow’s threats of Lithuania over Vilnius’ enforcement of EU sanctions against Kaliningrad, and Putin’s recent pledge to send nuclear-capable Iskander missiles to Belarus are additional worrying developments. It’s therefore important for NATO to keep re-iterating its red lines and to avoid foolishly risky moves such as establishing a no-fly zone in Ukraine. Putin is highly unlikely to respond to increased heavy weapons shipments with a nuclear strike, but Ukraine would be wise to keep its promises to refrain from striking Russian territory with Western artillery.

Is the arms race back?

On January 21, 2021, Green parties celebrated as the UN Treaty on the Prohibition of Nuclear Weapons (nuclear ban treaty), which prohibits nuclear weapons and aims for global elimination but isn’t supported by any nuclear power, came into effect. Just over a year later, the danger of nuclear proliferation grows as a result of the war in Ukraine. Many states may have concluded that if Ukraine had nuclear weapons, Russia wouldn’t have invaded. Others will take the lesson that the international community is helpless to stop nuclear states like Russia from aggression. “Russia can invade Ukraine and say to NATO, ‘If you get involved, you’re risking nuclear war, so back off.’ That seems to have been so far a pretty effective deterrent for Putin,” said Miller.

Nuclear powers are exceedingly unlikely to unilaterally eliminate their arsenals for the simple fact that it would leave them at a disadvantage vis-à-vis their nuclear adversaries. NATO’s 2010 Strategic Concept commits the alliance to “the goal of creating the conditions for a world without nuclear weapons, but reconfirms that, as long as nuclear weapons exist, NATO will remain a nuclear alliance.” But nuclear disarmament isn’t a naïve fantasy – the START treaty, the product of nearly a decade of disarmament talks and signed between the US and USSR in 1991, would eventually eliminate 80 percent of then-existing strategic nuclear weapons, an extraordinary accomplishment.

However, the much higher tensions of today mean that another such treaty is unlikely in the foreseeable future. Even before the war, the state of proliferation was already in dire straits after several arms treaties between Russia and the US were allowed to expire. “The tools that had governed total overall nuclear weapons – US-Russian arms control – are dying. There’s only one left,” Stein warned, referring to New START, an arms reduction treaty between Moscow and Washington that expires in 2026. After that, a new treaty will have to be negotiated, but as Stein worries, “in this political climate, I don’t know how that actually happens.”