Does Trump's nuclear testing raise the stakes – or are we already in an arms race?

President Donald Trump has announced the US will start testing nuclear weapons in what could be a radical shift in his nation’s policy.

“Because of other countries testing programs, I have instructed the Department of War to start testing our Nuclear Weapons on an equal basis,” Trump wrote on his social media platform, Truth Social, as he was about to meet the Chinese president on Thursday.

“That process will begin immediately.”

The world’s nuclear-armed states – those acknowledged as belonging to the so-called nuclear club and those whose status is more ambiguous – regularly test their nuclear weapons’ delivery systems, such as a missile that would carry a nuclear warhead.

Only North Korea has actually tested a nuclear weapon since the 1990s – and it has not done so since 2017.

The White House has not issued any clarifications to the commander-in-chief’s announcement. So it remains unclear whether Trump means testing nuclear delivery systems or the destructive weapons themeselves. In comments after his post, he said nuclear test sites would be determined later.

Six policy experts have told the BBC that testing nuclear weapons would raise the stakes in an already dangerous moment where all signs showed the world was heading in the direction of a nuclear arms race – even though it has not yet begun.

One of the six did not agree that Trump’s comments would have a major impact – and another did not think the US was provoking a race – but all said the world faced a rising nuclear threat.

“The concern here is that, because nuclear armed states have not conducted these nuclear tests in decades – setting North Korea aside – this could create a domino effect,” said Jamie Kwong, fellow in the nuclear policy programme at Carnegie Endowment for International Peace.

“We’re at a very concerning moment where the US, Russia and China are potentially entering this moment that could very well become an arms race.”

Darya Dolzikova, Senior Research Fellow for Proliferation and Nuclear Policy at the Royal United Services Institute (Rusi) – a London-based defence and security think tank – said Trump’s comments would change the situation massively.

But, she added, “there are other dynamics globally that have raised the risks of nuclear exchange and further proliferation of nuclear weapons levels higher than they have been in decades”.

Trump’s message, she said, “is a drop in a much larger bucket, and there are some legitimate concerns of that bucket overfilling”.

The experts pointed to escalating conflicts where one or more of the warring parties is a nuclear power – the war in Ukraine, for instance, in which Russian President Vladimir Putin has threatened at times that he could use nuclear weapons.

And then there were flare-ups – if not full-fledged conflicts – such as the one between Pakistan and India this year, or Israel – which has a policy of neither confirming nor denying it has nuclear weapons – attacking Iran – a country the West accuses of trying to build nuclear weapons (a charge Tehran denies).

Tensions on the Korean peninsula and China’s ambitions in Taiwan add to the overall picture.

The last existing nuclear treaty between the US and Russia that limits their amounts of deployed nuclear arsenals – warheads ready to go – is set to expire in February next year.

In his announcement, Trump said the US had more nuclear weapons than any other country – a statement that does not match figures updated regularly by another think tank that specialises in the field, the Stockholm International Peace Research Institute (Sipri).

According to Sipri, Russia has 5,459 nuclear warheadsm followed by the US with 5,177, an China coming a distant third with 600.

Other think tanks reported similar numbers.

Russia announced recently it had tested new nuclear weapons delivery systems – including a missile the Kremlin said could penetrate US defences and another that could go underwater to strike the US coast.

The latter claim may have led to Trump’s announcement, some of the experts suspected, even though Russia said its tests “were not nuclear”.

Meanwhile, the US has been watching China closely – with increasing concern that it will reach near-peer status, too, and posing a “two-peer nuclear risk”, experts said.

So a resumption of US nuclear testing could prompt China and Russia to do the same.

A Kremlin spokesman said that “if someone departs from the moratorium, Russia will act accordingly”.

In its response, China said it hoped the US would fulfil its obligations under the Comprehensive Nuclear-Test-Ban Treaty – which both countries have signed but not ratified – and honour its commitment to suspend nuclear testing.

Daryl Kimball, executive director of the Washington-based Arms Control Association, said a US resumption of nuclear weapons testing would be “a mistake of historic international security proportions”.

He said the risk of nuclear conflict “has been steadily rising” over several years and, unless the US and Russia “negotiate some form of new constraints on their arsenals, we’re likely going to see an unconstained, dangerous, three-way arms race between the US, Russia and then China in the coming years”.

Hans Kristensen, director of the Nuclear Information Project at the Federation of American Scientists, said the average person should be “very concerned” because there has been an increase over the past five years in nuclear warheads for the first time since the Cold War.

The last US nuclear weapons test – underground in Nevada – was in 1992.

Kimball said it would take at least 36 months to get the Nevada site ready for use again.

The US currently uses computer simulations and other non-explosive means to test its nuclear weapons, and therefore does not have a practical justification to detonate them, multiple experts said.

Kwong said there were inherent risks even with underground testing, because you must ensure there is not a radioactive leak above ground and it does not affect groundwater.

While blaming Russia and China for ratcheting up the rhetoric, Robert Peters, senior research fellow of strategic deterrence at the conservative Heritage Foundation, said that, while there may not be a scientific or technical reason for testing a warhead, “the primary reason is to send a political message for your opponents”.

“It may be necessary for some president, whether it’s Donald Trump or whomever, to test nuclear weapons as a demonstration of credibility”, he said, arguing it was “not an unreasonable position to hold” to be prepared to test.

While many others the BBC spoke to disagreed, all offered a fairly dire assessment of the current situation.

“My sense is that, if the new nuclear arms race hasn’t already begun, then we’re currently heading towards the starting line,” said Rhys Crilley, who writes on the subject at the University of Glasgow.

“I worry every day about the risks of a nuclear arms race and the increasing risk of nuclear war.”

The US tested the first atomic bomb in July 1945 in the desert at Alamogordo, New Mexico.

It later became the only country in the world to use nuclear weapons in warfare after dropping two atomic bombs on the Japanese cities of Hiroshima and Nagasaki in August of the same year during World War Two.