75 years after Hiroshima and Nagasaki, some experts believe the risk of the use of a nuclear weapon is as high now as it has been since the Cuban missile crisis.

The big picture: Nuclear war remains the single greatest present threat to humanity — and one that is poised to grow as emerging technologies, like much faster missiles, cyber warfare and artificial intelligence, upset an already precarious nuclear balance.

What's happening: A mix of shifting geopolitical tensions and technological change is upsetting a decades-long state of strategic stability around nuclear weapons.

• Strategic stability is when no country has an incentive to launch a first nuclear strike, knowing that doing so would inevitably lead to a catastrophic response. It's the "mutual" in "mutually assured destruction."
• Arms control deals like the Intermediate-Range Nuclear Forces Treaty are collapsing, while faster hypersonic missiles are shrinking the already brief minutes available to decide how and whether to respond to a potential nuclear attack, meaning "the possibilities of a miscalculation are unfortunately higher than they have been in a long, long time," says former Energy Secretary Ernest Moniz.
• As concerning as rising tensions are between the U.S. and Russia, or between the U.S. and a more assertive China, experts worry even more about the destabilizing effect of emerging technologies like cyber warfare and AI.
• "The black box of AI in the future of war makes it almost inherently unpredictable," says P.W. Singer, a strategist at New America and author of "Burn-In" — and unpredictability is anathema to a nuclear balance held in place by predictability.

Cyber warfare can directly increase the risk of nuclear conflict if it is used to disrupt command and control systems.

• But a greater danger may come from cyber conflict playing out in a space occupied by both military and civilian users, which risks eroding the bright line between nuclear and conventional war.
• U.S. policymakers have discussed whether to threaten a nuclear response to a wide-scale cyberattack on power infrastructure, which may serve as a deterrent, but also opens up a new and unpredictable escalation pathway to nuclear conflict.

AI is only in its infancy, but depending on how it develops, it could utterly disrupt the nuclear balance.

• AI may eventually help war planners more effectively target an enemy's nuclear weapons. That would make an opponent more vulnerable — and potentially more willing to use nuclear weapons first out of a fear they might lose them.
• As Singer notes, "just like any human, AI can suffer from various biases" — especially since there is no real-world nuclear war data to train it on.
• But unlike a human, the smarter AI gets, the harder it is for humans to understand how it works, and whether it's making a mistake in a realm where there is no room for mistakes.

Be smart: As analysts from RAND wrote in a 2018 report, "AI may be strategically destabilizing not because it works too well but because it works just well enough to feed uncertainty." Whether or not an AI system could provide a decisive advantage in a nuclear standoff, if either the system's user or that country's opponent believes it can do so, the result could be catastrophic.

• Yes, but: Singer also offers a more hopeful scenario where effective AI could reduce the risk of human miscalculation by "offering far greater information in scale and detail than was possible in the past."

The bottom line: The riskiest period of the Cold War was its earliest stages, when military and political leaders didn't yet fully understand the nature of what Hiroshima had demonstrated. Emerging technologies like AI threaten to plunge us back into that uncertainty.

There are roughly 13,355 nuclear weapons in the world, with 91% of them belonging to Russia (6,370) or the U.S. (5,800), according to estimates from the Bulletin of Atomic Scientists, my Axios colleague Dave Lawler and I write. 

• China’s stockpile of around 290 warheads is “likely to grow further over the next decade” and put it firmly in the third spot among the world’s nuclear powers, according to analysts Hans Kristensen and Matt Korda.
• France (300) and the U.K. (215) both have significant stockpiles, as do rival nuclear powers Pakistan (150) and India (130). 
• Israel has never confirmed or denied possessing nuclear weapons, but it's believed to have secured the bomb in 1966 or 1967, and now possess around 80 warheads.
• North Korea, meanwhile, has embraced its status as a new nuclear power. As of 2019, the analysts put its stockpile at 20–30 warheads.

Timeline: The U.S. was first to the bomb, conducting its Trinity test 75 years ago last month.

• The Soviet Union conducted its first nuclear test in 1949, far earlier than U.S. officials had expected.
• The nuclear club grew as the U.K. (1952) and later France (1960) conducted tests.
• The Chinese, after initial Soviet help, tested a nuclear weapon in 1964.
• The 1968 Nuclear Non-Proliferation Treaty has helped limit the size of the club, though India (1974), Pakistan (1998) and North Korea (2006) brought its membership to nine, including Israel.

The bottom line: The drastic reduction in the total nuclear warheads since the height of the Cold War has reduced the danger of a world-ending war. But with new players joining the game since then and evolving technologies, nuclear chess has become more complex than ever.

A massive explosion that rocked Beirut yesterday was so large that some observers initially wondered if it could be the result of a nuclear bomb.

Why it matters: Experts quickly determined the explosion was non-nuclear, and it appears to be the result of fire reaching a huge cache of ammonium nitrate. But the fact that even this enormous blast was just the fraction of the size of a small atomic bomb gives us some sense of the devastation that would result from a real nuclear detonation.

The Beirut explosion lacked two hallmarks of a nuclear detonation: a blinding white flash and a thermal pulse that would scorch those within the blast radius.

• Videos showed that the explosion did have the mushroom cloud most commonly associated with a nuclear bomb. But there's nothing specifically nuclear about the effect, known as Wilson clouds, which occur when humid air gets compressed and causes the water in it to condense.

The explosive power of the blast added up to approximately 240 tons of TNT, according to one estimate shared online by a nuclear expert.

• That is as big as it appeared in online video. The largest conventional bomb in the U.S. arsenal, the MOAB, has the explosive power of approximately 11 tons of TNT.

Yes, but: As terrible as it was, the Beirut blast was less than 2% the size of the Hiroshima bomb, which had the explosive power of 15,000 tons of TNT.

• The B83 nuclear warhead, the largest in the current U.S. arsenal, has 80 times the explosive power of Hiroshima's Little Boy, at 1.2 million tons of TNT equivalent.
• The death toll is of a different magnitude as well. As of Wednesday afternoon at least 135 people had been killed by the Beirut blast. At the low end of estimates, 70,000 people were killed at Hiroshima.

Of note: Historian Alex Wellerstein's NUKEMAP site allows you to simulate the effects of a nuclear strike anywhere around the world.

• I dropped the equivalent of a B83 bomb on my head in Brooklyn. The expected fatalities were more than 1.4 million.

Other nations are catching up to U.S. capabilities in space, potentially putting American assets in orbit at risk, writes Axios' Miriam Kramer.

Why it matters: From GPS to imagery satellites and others that can peer through clouds, space data is integral to U.S. national security.

• Those same assets make for appealing targets by bad actors, and experts are concerned that weapons testing in orbit could lead to U.S. satellites being attacked in the future.
• "As the number of spacefaring nations grows and as some actors integrate space and counterspace capabilities into military operations, these trends will pose a challenge to U.S. space dominance and present new risks for assets on orbit," the U.S. Defense Intelligence Agency wrote in a 2019 report.

The big picture: Norms of behavior have largely prevented nations from using destructive weapons against one another in space.

• But as anti-satellite and other counter-space threats become more common, experts say the U.S. needs to work to foster international partnerships that will help prevent destructive tests and attacks in the future.

My thought bubble: The possibility of conflict in space raises the risk of nuclear war as well, given America's dependence on satellites for detection of missile launches and command and control.

Read the full story

Will COVID-19 kill cash? (Howard Davies — Project Syndicate)

• Don't expect paper money to disappear overnight, but the pandemic will be one more factor moving consumers toward cashless payments.

The panopticon is already here (Ross Andersen — The Atlantic)

• A dark take on the state of AI-enabled surveillance in China that asks whether its future could be ours as well.

The truth is paywalled but the lies are free (Nathan Robinson — Current Affairs)

• An entertaining screed that gets at an essential kernel: as legitimate news publications turn to paywalls, free news may increasingly mean fake news. (Except at Axios, of course.)

The pandemic response that wasn't (Carrie Arnold — Hopkins Bloomberg Public Health Magazine)

• All the ways — the many, many ways — the COVID-19 response didn't go as scripted.

The Soviet Union built a partially automated nuclear launch system that would have enabled Moscow to respond even if the entire country had been essentially destroyed by an American attack.

Why it matters: Of all the mad acts in the Cold War, creating an actual doomsday machine may have been the maddest. But the history of the Soviet system has sobering lessons for a future where AI will take a more active role in nuclear strategy.

How it works: Called "Perimeter," but better known within the Soviet military as "Dead Hand," the system contained sensors that could detect signs of nuclear explosions in Soviet territory.

• If an explosion was detected, the system would check communication links with the Soviet General Staff.
• If the line went dead, the system would transfer launch authority to whoever was manning a protected bunker, and that person — even if they were a junior officer — could launch all remaining missiles.

Context: When Perimeter was developed in the 1980s, the Soviets feared U.S. strategic missile defense would erode the deterrence of their nuclear arsenal.

• But Perimeter, as Wired's Nicholas Thompson wrote in 2009, could "convince the enemy that you can strike back even if you're dead."
• Of note: A version of Perimeter may still be operational in Russia today.

If this sounds familiar, there's a version of the doomsday machine in Stanley Kubrick's 1964 nuclear satire "Dr. Strangelove," which does indeed bring about the apocalypse at the end of the film, all to the tune "We'll Meet Again."

• Another parallel: The existence of Perimeter, like the doomsday machine in "Strangelove," was never made public.
• Which, as Strangelove himself notes in the film, rather defeats the point of a doomsday machine.