Last Thursday, President-elect Donald Trump issued a few statements (guess where) about America's military, with this statement as a kicker: "The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its sense regarding nukes." Though much remains to be seen about how Trump's tweets will actually translate into policy, it seems likely that nuclear war will be back on the table. Are we going to roll back decades of policy and technology to return to the Atomic Age?

Despite Trump's assertion, the world has come to its senses about nukes (and not just in Hollywood). Political consensus over issues like denuclearization has been fairly stable since the 1980s, thanks in part to scientific researchers showing what would happen to a world ravaged by nuclear bombs. One such study was The Medical Implications of Nuclear War, published by Fred Solomon and Robert Q. Marston in 1986. This rigorous and grim estimate of nuclear war's effects on our planet is written in a bleak manner for good reason: to scare us straight.

"Our national security for the past 40 years has been based on the perception that nuclear war would be unhealthy," the study begins. "Understanding what the health consequences of a nuclear war would be, as best we can know them, is very important for informed opinions and actions by citizens and by government."

It seems we're due for a reminder.

Bright, hot, then cold

Nuclear war offers a multitude of bad ways to die. The bulk of the initial deaths from a nuclear bomb come from the intense heat from the detonation itself, followed by the firestorms triggered by the blast. Extrapolating from the incendiary bomb attacks in World War II (Tokyo and Dresden being among the more infamous), the authors note, “the projected number of injured requiring medical treatment would be drastically reduced relative to that projected by blast scaling, as many injured that would otherwise require treatment would be consumed in the fires.” If not vaporized at the center of a blast, many of those who survive the initial moments would then promptly be burned alive by a raging super-fire extending for many kilometers from the hypocenter of the blast.

Almost all of the energy of a nuclear bomb (fission or fusion) is released as very short wavelength light, in the X-ray range. These soft X-rays are rapidly absorbed by the surrounding air, heating it to immense temperatures. The result is the characteristic rapidly expanding fireball you’ve seen in stock film of nuclear explosions. For a one megaton airburst fusion bomb, the initial fireball is about 1.6 km (one mile) in diameter.

Shockwaves follow, demolishing structures and tearing apart human beings for miles. For a one-megaton airburst bomb, the EM radiation released is sufficiently intense to spark fires for about a 12km diameter circle around the detonation site, resulting in an enormous firestorm. The rapidly rising column of superheated air over the firestorm generates its own wind, drawing in more material, stoking the fire, and leading to a further expansion of the conflagration.

Noxious gases from burning things that make up cities will increase the death toll by suffocating and poisoning a significant percentage of those not burnt alive from the initial blast and firestorm.

The net result is that as horrible as the human consequences of the Hiroshima and Nagasaki bombings were, modern nuclear weapons are much more likely to generate gigantic firestorms (easily a hundred square miles around an American city). With the rosier projections, there would be no survivors within a 4km radius from an air-burst one-megaton bomb over a city; all within that radius would be expected to die within minutes of the detonation. People would be severely injured for at least 18km from the center of the blast—in vast and overwhelming numbers. If one considers the effects of the resultant firestorms, it’s reasonable to expect no survivors within 10km of such a blast. (For quick reference, all of Manhattan is roughly 60 square km.)

Emerge from bunkers, battle superfires

For those who don’t perish in minutes or hours following the blast itself, the environmental consequences of a nuclear exchange become the next nightmare. The nuclear blast and resultant superfires will create massive amounts of black soot (the charred remains of the people, buildings, plants, and other material that made up the city), about 50 percent of which will be injected into the upper troposphere or stratosphere levels of the atmosphere—well above the heights where soot can be rapidly cleared. The remainder will fall as intensely radioactive black rain upon the straggling survivors below. The dark smoke high in the atmosphere will block out the Sun.

Regions below the cloud could see about a 20- to 40-degree Celsius local reduction in temperature within about a week (more during summer months, somewhat less in winter), with the most severe temperature drops persisting for weeks to months. The dramatic change in temperature would then drive winds that would further spread the cloud and the effect. The result is nuclear winter. Slowly, over years, the radioactive dust will drift down to the surface, eventually letting sunlight back through as temperatures gradually return to normal.

Radiation, curiously, contributes relatively little to the overall immediate misery after a nuclear war. The area surrounding a blast site remains intensely radioactive for days to weeks—with weather playing a big effect on the exact spread and locations of the more intense radioactivity. But radioactivity decays exponentially; the long-term effects are subtler, insidious, and include increased rates of cancer.

Exotic chemical changes to the atmosphere are possible, particularly in a larger war over multiple cities, with complex petrochemicals brewing in the upper atmosphere and comprehensive destruction of the ozone layer allowing much more ultraviolet radiation to reach the surface when sunlight returns. This results in a damaging "UV spring" following the nuclear winter. The projections here become less certain, as we lack the data to develop the right models.

Bunkers and shelters can attenuate some of the effects (mostly from the radiation, provided one is far enough away to avoid the blast and firestorm). A survivor of a nuclear war in which many nuclear devices are detonated would then contend with crumbling societies, failing crops, and chaotic, disturbed weather. For a large war, the end of modern life as we know it is probable; the extinction of humans as a species is possible.

"Everything needed for thinking clearly"

The aftermath of even a single nuclear detonation over an urban center is surreal in the sheer scope and nature of the horror induced. A larger nuclear exchange of hundreds or thousands of devices is and should be mortally terrifying to consider. Nuclear war is often described as unthinkable, but "unthinkable" is the wrong word.

In the study's forward , Dr. Lewis Thomas emphasizes the importance of researching the aftermath of such catastrophe: “Unthinkable is the word for whatever is in front of our eyes but too big to figure out, too frightening. Pay attention, in this book, to the doctors and the scientists here assembled. Everything needed for thinking clearly, wincing all the way but thinking anyway, is written down in these chapters. Anyone, any age, can read what's here and understand what we could be in for if we stay on this road. What to do is another matter, but at least the facts of the matter are laid out here. You'd better bet your life it's thinkable.”

In an era where our leaders look past the worst possibilities with blind optimism, it’s important once again to wince, read, think, and describe the "unthinkable."

Jonathan Golob is an MD-PhD physician scientist and science writer based in Seattle, Washington. His takes on modern science and medicine can be found at The Stranger and at his own personal site. His primary research interest is human microbiome research.