As with guns, Americans are divided on the issue of nuclear weapons. One side is motivated by a “more is better” philosophy — a deep, intuitive belief that the best way to stop bad guys is to get more weapons to the good guys. On the other side are those who think we’d be safer with fewer weapons — and not just because of the risk of conflict. After all, as a country’s nuclear arsenal grows, so too does the chance of accidents.

U.S. President-elect Donald Trump seemed to endorse the “more is better” view in his recent tweet saying that America needs to “strengthen and expand its nuclear capability.” It’s a view that’s shared by at least one professor of government, as well as Republicans in Congress, who, under the Obama administration, made “modernizing” U.S. nuclear forces a condition for approving the New START Treaty, the latest arms control agreement between the U.S. and Russia.

But scientists tend to agree with the less-is-safer philosophy. Some are guided by more than intuition, having spent careers studying what would happen following the exchange of modern nuclear weapons — bombs vastly more powerful than those the United States dropped on Japan in World War II.

Unlike a massive conventional bombing, nuclear weapons would have long-term environmental effects, from deadly fallout to raging “superfires” that would burn entire cities, lofting enough soot into the stratosphere to dim the sun for a decade. No country could launch an attack without raining death on people around the globe, including its own.

Russia and the U.S. each have about 7,000 nuclear weapons, 2,000 of which are deployed. “If someone launches a first strike and the other side doesn’t do anything about it, everyone in the first country is still going to die from climate effects,” said Rutgers University climatologist Alan Robock. “So if you attack, you are a suicide bomber.”

Robock, along with the late scientist Carl Sagan, were among the first to recognize the threat of nuclear winter — the nightmarish scenario in which soot would darken the skies and lead to a decade of year-round freeze. While the end of the Cold War weakened concerns that nuclear war would happen, modern climate modeling techniques have strengthened the case that global cooling would result from it.

The bombs dropped on Hiroshima and Nagasaki weren’t large enough to trigger nuclear winter, he said, but a modern nuclear war will play out on a different scale. One Trident submarine carries the destructive power to create 1,000 Hiroshimas, and the U.S. has 14 of them, Robock said. If the Russians respond in kind, he said, that’s 2,800 Hiroshimas, stemming from about 1 percent of the world’s nuclear arsenal.

More recently, he’s calculated that catastrophic global cooling would follow even a “small” nuclear exchange between India and Pakistan, both armed with around 100 nuclear weapons. “People think nuclear weapons are good and more is better,” he said. “But they don’t understand that the consequences of using them are quite different from using conventional weapons.”

And there are reasons to worry about accidental nuclear war. In 1979, U.S. missile crews in the Midwest picked up the warning of a massive Soviet attack. It turned out to be a mistake — someone had put a training tape simulating such an attack in the wrong computer at the U.S. Strategic Air Command’s headquarters in Colorado. In 1983, the Soviets got a signal from their satellites that the U.S. had aimed five nuclear missiles their way. It turned out to be the result of sun reflecting off clouds. And the threat didn’t end with the Soviet Union. In 1995, the Russian early detection system was triggered by a science experiment launched from an island off Norway.

Despite these brushes with catastrophe, hundreds of weapons in silos and on submarines are still poised on “hair-trigger alert,” according to physicist Frank von Hippel, co-founder of Princeton University’s Program on Science and Global Security.

What that means is that if U.S. satellites detected a possible Russian missile launch, Trump would have about 30 minutes to decide whether to launch a massive strike. Putin would have even less time to make the same decision, since Russia lacks the early warning satellites the U.S. depends on.

Ostensibly in the interest of making the world safer, the U.S. is pouring $1 trillion into a “modernization” effort aimed primarily at improving the accuracy of the country’s missiles. Assuming the U.S. would not start a nuclear war, the primary rationale for modernization is psychological — a message to the world’s other nuclear states that the U.S. has superior nuclear forces. But von Hippel and other scientists worry this will backfire. The Russians see the effort to improve U.S. missiles as a preparation for a first strike, said Theodore Postol, a professor emeritus in MIT’s department of science, technology and society. And that alarm could make Russia more likely to confuse an ambiguous signal for the real thing.

Add to this concern the fact that the Russians don’t have very good vision, said Postol, who has degrees in physics and nuclear engineering. He started analyzing the Russian early warning system after the 1995 incident, when a rocket aimed for the North Pole to study the aurora triggered a full-scale nuclear alert. He concluded that the Russians had an incomplete view, provided by a few satellites and partial radar coverage, and lacked the technology to build detectors comparable to the ones the U.S. depended on its satellite warning system. That the U.S. was unaware of the holes in Russia’s detection system was “a massive intelligence failure that could have had catastrophic consequences,” he said.

Since then, he said, the Russians decided to scrap the satellites and invest in more complete ground-based detection, which gives them only minutes to decide whether to launch a counterattack. “In short, the Russians would have no choice but to plan for the possibility they would have no more than four to 10 minutes before an attack from U.S. submarines destroys Moscow,” Postol said.

In his view, the U.S. could make the world safer by improving Russia’s defenses — for example, by helping to build a warning system that would reduce the risk of false alarms. He suggested such a gesture would send a message that the U.S. is not interested in launching a first strike. “The time lines are very short,” he said. “And you are talking about Armageddon.”

Science writer Faye Flam is a Bloomberg View columnist.

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