The world just passed a surprisingly positive milestone on nuclear weapons

The post-war international order may be tearing apart at the seams and international law is increasingly looking like a polite fiction, but we did just pass one notable milestone of global peace and stability: As of this month, the world has gone the longest time without a nuclear explosion since the atomic era began more than 80 years ago.

The last nuclear test took place in North Korea on September 3, 2017. The previous longest period without a detonation was between May 30, 1998, when Pakistan conducted its last test, and October 9, 2006, when North Korea conducted its first. We reached the new record on January 14, and are now at eight years, four months and 21 days.

Though they’ve only been used in war twice since their creation in 1945, Dylan Spaulding of the Union of Concerned Scientists noted in a recent blog post that “at least eight countries have detonated more than 2,000 nuclear weapons” over the years, all in tests. (For a mesmerizing and disturbing visualization of these nuclear tests, I recommend this time-lapse animation by the Japanese artist Isao Hashimoto, which runs to 1998.)

It’s difficult for people today to imagine just how constant nuclear detonations were in the first decades after Hiroshima. At the height of the testing era in the late 1950s and early 1960s, dozens of nuclear tests were taking place every year. Most of those tests were done above ground, marked by iconic mushroom clouds.

The detonations were the visible backdrop to rising fears of a civilization-ending nuclear war, which at times seemed not just possible but inevitable. (The Pentagon Papers leaker Daniel Ellsberg, who worked for the national security think tank the Rand Corporation in the late 1950s, wrote in his memoir that he never joined the company’s retirement fund, because he assumed the world would end in nuclear holocaust.) Nuclear conflict was a dominant and ever-present theme in global politics, a reality that, for all the geopolitical instability of our current era, most people alive today have never experienced.

In addition to being provocative and destabilizing political acts, these tests have, for decades, been linked to increased rates of cancer, autoimmune disorders and other health conditions among the “downwinders” living near testing sites. The effects may be wider-ranging than that: a report released this week by the NGO Norwegian People’s Aid estimated that nuclear testing may have caused as many as 4 million premature deaths from cancer and other conditions.

It was partially out of growing fear of the radioactive effects of these detonations that the world began gradually phasing out testing, starting with the 1963 Partial Test Ban Treaty that prohibited above-ground detonations. That treaty — the first time global powers agreed to shared limits on nuclear weapons — set the stage for more comprehensive nuclear arms control agreements between the US and Soviet Union.

The end of the Cold War arms race dramatically reduced the pressure for more field experiments involving nukes. One hundred and seventy-eight countries have ratified the 1996 Comprehensive Nuclear Test Ban Treaty (CTBT), which prohibits all nuclear testing. The United States signed the treaty under President Bill Clinton but has never formally ratified it. Nonetheless, it has observed a moratorium on testing since its last detonation, conducted underground in Nevada in 1992. The last Russian test was in 1990.

When a test isn’t a test

From the earliest days of the nuclear era, scientists questioned whether these tests were necessary at all. After the bombings of Hiroshima and Nagasaki, we knew that these weapons worked. Robert Oppenheimer, the “father of the atomic bomb,” declined to attend the first postwar US nuclear test at Bikini Atoll in 1946, writing to President Harry S. Truman that testing wouldn’t reveal anything about the bomb that couldn’t be deduced from “simple laboratory methods.”

Some nuclear tests, like the record-setting “Tsar Bomba” set off by the Soviet Union — a 50-megaton warhead that was over 3,300 times more powerful than the bomb dropped on Hiroshima — may have been about projecting a powerful image as much as obtaining practical research data.

Those “laboratory methods” have only gotten more sophisticated since then. When the world passed the record on January 14, I happened to be in Los Alamos reporting for a forthcoming story on how the lab that Oppenheimer built is now integrating artificial intelligence into its advanced modeling work, which includes ensuring that America’s nuclear weapons will work the way they’re supposed to in the hopefully unlikely circumstance that we ever decide to use them.

But there are worrying signs that the pause on tests may not last indefinitely. In October, President Donald Trump called for the US to resume nuclear testing. It’s not clear if any work has actually begun to make that happen, and it would probably be years before the US would be ready to test again, but the idea is gaining support amid a new nuclear era in which China is building up its arsenal and Russia is increasing its nuclear saber rattling. Next month, New START, the last remaining nuclear arms control agreement between the United States and Russia, will lapse, and there’s little momentum toward replacing it.

Advocates, including the drafters of the conservative Heritage Foundation’s “Project 2025,” argue that a return to testing is necessary not so much for technical reasons, but as a demonstration of the credibility of America’s nuclear deterrent. But in a recent essay in Foreign Affairs, Siegfried Hecker, former director of Los Alamos National Laboratory, warned that “a return to testing at this time would likely benefit U.S. adversaries more than it would the United States. Worse still, it might rekindle an even greater and broader arms race than in the first few decades of the Cold War.”

We’re not there yet, but the recent signs aren’t good. In 2023, Vladimir Putin withdrew Russian ratification of the CTBT, citing the US failure to ratify the treaty. US intelligence services have also suggested China may be conducting small nuclear tests, though not at the level that would violate the CTBT.

Put those developments together with Iran’s set-back but not abandoned nuclear program and increasing support for nuclear weapons among US allies who are less sure than ever about American security guarantees, and the future of the pause is far from certain.

We were lucky to survive the era of constant nuclear testing, and we’re fortunate to still live in a moment where years can go by without a detonation. In many ways, given how dire things looked in the past, it’s the ultimate good news story. But it remains to be seen whether we’ll maintain that luck.

A version of this story originally appeared in the Good News newsletter. Sign up here!