By Andreas Kluth / Bloomberg

Too bad we as a species don’t have the luxury of worrying about just one existential threat at a time. We’re already rather busy with one — a pandemic — and about to talk our heads off about another —climate change — at the COP26 convention in Glasgow. Now we’re also reminded of a third: nuclear annihilation.

This summer, China apparently tested new hypersonic missile systems; as recently revealed by the Financial Times but officially denied by Beijing. What’s shocking about this isn’t that these new weapons can travel at about five times the speed of sound; existing ballistic missiles can go even faster. It’s that these new Chinese birds can glide around the world inside the atmosphere in any direction they want, while being guided remotely to their target.

If you don’t immediately find that innovation scary, take it from Mark Milley, who as chairman of the Joint Chiefs of Staff is America’s top brass. Speaking to Bloomberg this week, he called the demonstration of Chinese missile prowess “very close” to a Sputnik moment. Long before it became a vaccine, you recall, Sputnik was the eponymous satellite launched in 1957 by the Soviet Union that suggested the Russians were ahead in the space race and could one day rain nuclear bombs down on the U.S. from the sky.

Whether the analogy is apt or not, this latest development does add to many others to warrant grave concern. Think about why China might want such a hypersonic glide vehicle as a transport option for its small but fast-growing arsenal of nuclear warheads. The most obvious purpose is to evade U.S. missile defenses already existing or in development.

The U.S. has systems in Alaska that, fingers crossed, could shoot down an incoming ballistic missile from North Korea (the ostensible foe) or any other adversary on that side of the earth, including China. These missiles would have to follow a fixed trajectory out of the atmosphere, fly into space and over the North Pole and then back down toward their targets. Out there in the ether is where the American interceptors would hit.

The U.S. is also adding interceptor systems based on ships in the Pacific, as a successful test proved last year. These could stop missiles lobbed from Asia to North America over Hawaii, for instance.

If China — and then Russia and other nuclear powers — get gliders, however, these defensive systems will be obsolete. Nuclear payloads could then zip around the South Pole instead, for instance. They’d never even exit the atmosphere. And they could change their trajectory, being controlled all along by a Chinese operator with a joystick.

All this makes China sound menacing and aggressive. In that sense, the news seems to rhyme with revelations that China is also building a couple of hundred silos for more conventional intercontinental missiles that could carry nukes.

In reality, China probably appears so aggressive only because it feels incredibly insecure. The greatest fear in Beijing is that in an escalating conflict — over Taiwan or whatever else — the U.S. might be tempted one day to launch preemptive nuclear strikes to take out all or most of China’s arsenal. The Americans would only contemplate such a drastic step, of course, if they thought that their own defenses could parry any remaining missiles coming from China in retaliation.

That would explain the Chinese missile silos, most of which are probably destined to be empty decoys to keep the Americans guessing where the real warheads are. It would also explain these new gliders. They send the message that, hey, we don’t need to lob our kit over the North Pole, we could go around the other side.

Such mental games — and they do ultimately originate in mathematical game theory — demonstrate once again how, in the perverted logic of nuclear war, everything is interconnected. An escalation in defensive technology, in this case American, might superficially seem pacific and uncontroversial. But by changing the parameters of the game, it can trigger an arms race in offensive weapons.

This is also the infernal subtext when the U.S. and Russia, still the two largest nuclear powers by far, talk about “modernizing” their arsenals. This means not only more delivery methods, hypersonic and what not, but also new types of nukes, including “tactical” ones.

Cold War game theory was based on concepts such as Mutual Assured Destruction: MAD, appropriately. If either side launched “strategic” weapons at the other’s homeland, it would swiftly receive the counterstrike. Like two people with a matchbox standing in the same room with gasoline up to their waists, neither would ever light up first.

Tactical nukes ruin that metaphor. They carry smaller payloads that are intended for use not against the adversary’s homeland but against enemy forces in a war zone. Imagine, say, Russia fighting and losing against NATO in eastern Europe, or the U.S. coming up short against China in the South China Sea. Either could then be tempted to end the regionalized battle on its terms with a “limited” nuclear strike.

But that opens Pandora’s strategy box. Would a tactical strike warrant retaliation, and if so, of the tactical or strategic sort? How human-all-too-human leaders would calculate their options in such an escalation spiral — where decisions must be taken in minutes — is an open question. But on balance, the scenarios are more — rather than less — calculable if all sides retain an ability to retaliate.

As ever, understanding our common dilemma — not as Americans, Russians or Chinese, but as humans stuck together on a confusing and tense planet — is the first step toward sanity. It’s fine for the world’s great and middle powers to compete as rivals in ideology, trade and whatever else. But their leaders must accept that when it comes to existential threats to humanity, they must rise above themselves and talk as partners. That’s true whether the specter is a pandemic, climate change, or nuclear war.

Andreas Kluth is a columnist for Bloomberg Opinion. He was previously editor in chief of Handelsblatt Global and a writer for the Economist. He’s the author of “Hannibal and Me.”