Vladimir Putin’s declaration that he is moving Russia’s nuclear deterrent to “special alert” has upped the stakes in the stand-off with the West over Ukraine.

John Erath, senior policy director at the Center for Arms Control and Non-Proliferation in the US, talks to Reaction about how we should interpret this latest escalation.

Do we know exactly what moving Russia’s nuclear deterrent to a “special mode of combat duty” means? And why has Putin made this announcement now?

I certainly don’t know exactly what it means and I would suppose that the ambiguity is intentional.

Since there is no particular set of circumstances that would warrant a nuclear war at this point, Putin has done this to send a message.

We can read it as a warning – to the US, Europe, Japan and all the others that are currently taking action against Russia – to stop.

Conflict between Russia and Ukraine has been going on for seven years now and Ukraine has been developing capabilities to resist aggression this whole time. Ukraine has experienced forces out there to defend their country. But Putin thought military action would be quick and relatively bloodless, much as it was in 2014. So when Russian forces have encountered resistance, it’s very hard for them to accept that this is resistance of Ukrainian people. It’s an easy logical jump to suppose that foreign assistance has something to do with the unexpected resistance.

Does this announcement from Putin come as a surprise?

This is a fairly standard move from the playbook that Putin runs. He finds what people are most concerned about and threatens it. He has heard commentators in Washington, London, Berlin saying “this conflict should not lead to nuclear war” and he understands that this possibility is very concerning to all of us: i.e. that a conflict involving a nuclear power could end up with the use of nuclear weapons. So he’s trying to push that button.

How worried should we be about the risk of nuclear escalation? And can we count on the logic of mutual assured destruction to protect us?

I think there’s nobody that wants to see a nuclear war.

Putin is going to be very careful to not step over the line and take actions that would provoke a nuclear response from NATO. Despite what some people say, I don’t think he is insane. And he is going to calculate that very carefully.

On the other hand, he knows that everyone else feels that way as well. He knows that the policies determined in NATO capitals are going to be calculated to minimise the risk that the conflict takes on a nuclear dimension.

What about the threat of smaller scale nuclear attacks – Russia using shorter-range, tactical nuclear weapons with lower explosive yields?

You’ve identified what is one of the real significant risk factors here.

The Russians do have the use of weapons including non-strategic weapons as part of their military doctrine. Indeed, Russian military doctrine involves integrating their nuclear forces with their conventional forces. They don’t have as firm a line as we have in other countries.

It is certainly possible that they would consider using a non-strategic weapon to achieve something. But it’s hard to say in military terms exactly what that “something” would be, because nuclear weapons are rather indiscriminate in their destruction.

I think that the global opprobrium that would ensue from any use should be deterrent enough. But as Russia grows more desperate, the risk of that very act grows.

What is the best way for Ukraine’s allies to respond to this threat? Do Western nuclear forces need to go on higher alert?

I think it would be a huge mistake to move the nuclear forces to a higher alert level. They are already on a fairly high alert level. And if the unthinkable were to happen, I think there would be sufficient warning to come up with an appropriate response.

The key question is not the alert level, but how to deter consideration of the use of nuclear weapons on the part of Russia.

There has got to be a very clear line drawn from every world leader – not just in the West – that using nuclear weapons in the Ukraine conflict would be unacceptable.

In the meantime, the governments that are considering adding sanctions should add sanctions right now. We need to make it very clear that the cost of aggression against Ukraine is high and getting higher until that aggression stops.

That also means we must stop buying Russian energy. It’s a war and people are going to have to undergo some hardship – higher prices for fuel, higher prices for energy at home. When we consider the price that the people of Ukraine are paying, it is a small price that we can pay.

The Russian economy is heavily dependent on its exports of gas and oil. So energy sanctions are hitting them where it hurts. It’s not something that is going to take immediate effect but it will have a growing effect on Russia. As this crisis goes on, they will find it impossible to supply their war machine with the cash to keep it going.