APART from the fanciful doomsday threats mentioned in the preceding article, there are concerns that merit serious consideration. Many people worry about overpopulation and the water and food shortages it may bring. Others fret about the consequences of a global financial collapse. What about natural disasters, epidemics, or nuclear war? Could such events bring about a global catastrophe?

Let us consider briefly some commonly discussed doomsday scenarios. Not all threaten to kill everyone on earth, but they certainly appear to have the potential to bring doom to civilization as we know it. They include the following.

In 1991, Mount Pinatubo erupted in the Philippines, killing more than 700 people and leaving some 100,000 homeless. A huge cloud of ash rose 19 miles (30 km) into the sky and then fell to the earth, burying crops and causing the roofs of buildings to collapse. Pinatubo and other volcanoes like it cause changes in climate for several years after erupting.

Super eruptions, such as those that have occurred in the distant past, would be hundreds of times larger and more devastating than any eruptions in recorded history and would do far more damage. Apart from the immediate destructive power, global climate change would cause crop failure, disrupt food supplies, and lead to mass starvation.

“Volcanoes kill plants and animals for miles around; supervolcanoes threaten whole species with extinction by changing the climate across the entire planet.”​—National Geographic.

Early one morning in 1908, a man was sitting on the front porch of a trading post in Vanavara, Siberia, when an explosion flung him from his chair. The heat was so intense that he felt as though his shirt were on fire. Ground zero for that explosion was some 40 miles (60 km) away. The blast was caused by an asteroid that was about 120 feet (35 m) in diameter and weighed approximately 220 million pounds (100 million kg). After entering earth’s atmosphere, the asteroid exploded as a result of the pressure and the heat of its descent. The explosion released energy equivalent to 1,000 Hiroshima-sized bombs and flattened some 800 square miles (2,000 sq km) of Siberian forest. A larger asteroid, of course, would do much more damage, generating immense firestorms, which would be followed by plummeting global temperatures and major extinctions.

“Throughout earth’s history, we have been bombarded by comets and asteroids from space. Impacts happened more frequently in the past, but they will happen again. It is just a matter of when.”​—Chris Palma, senior lecturer in astronomy and astrophysics at Penn State University.

Scientists believe that a rise in the earth’s average temperature, extremes in weather, the melting of ice caps and glaciers, and the death of coral reefs and important species all point to global climate change. Though the subject is debated, many hold the cause to be the burning of coal, oil, and natural gas​—fossil fuels that emit high amounts of carbon dioxide into the atmosphere—​by cars and industry.

Some experts believe that those emissions act like a greenhouse, slowing the escape of heat from the earth into space and causing temperatures to rise. Because trees absorb carbon dioxide, large-scale deforestation may also contribute to climate change.

“If present rates of global warming continue and production of carbon dioxide is not curtailed, many scientists believe the Earth’s average temperature will continue to rise, resulting in wilder and more unpredictable climatic swings and higher ocean levels that could threaten the low-lying coastal areas where much of humanity makes its home.”​—A Mind for Tomorrow: Facts, Values, and the Future.

In the 14th century, the Black Death wiped out a third of the population of Europe in just two years. Between 1918 and 1920, the Spanish flu killed at least 50 million people. Slow methods of travel impeded the spread of those diseases. However, with the growth of cities and the ease of international travel today, a similar disease could rapidly spread across all continents.

Such a pandemic disease could be a natural occurrence. But there are also growing fears of biological weapons, man-made diseases. Experts in the field say that a small group of people who are trained in key disciplines could buy equipment on the Internet and produce deadly biological weapons.

“Naturally occurring disease remains a serious biological threat; however, a thinking enemy armed with these same pathogens​—or with [multidrug-resistant] or synthetically engineered pathogens—​could produce catastrophic consequences”​—The Bipartisan WMD Terrorism Research Center.

Over the past five years, beekeepers in the United States have lost about 30 percent of their bees each year on account of colony collapse disorder, a global phenomenon in which entire colonies of bees abruptly and mysteriously disappear from their hives. Bees do more than provide us with honey. They pollinate key crops, including grapes, apples, soybeans, and cotton. We depend on bees.

We also depend on phytoplankton. Without it we would have no fish. Without worms to aerate the soil, we would have far fewer crops. The extinction of such key species would result in food shortage and starvation, leading to violence and riots. Pollution, overpopulation, overharvesting, habitat destruction, and climate change contribute to the extinction of animal species perhaps as much as 1,000 times more than natural rates.

“Every year, between 18,000 and 55,000 species become extinct. The cause: human activities.”​—United Nations Development Program.

One nuclear explosion can instantly obliterate a city​—a somber fact that was demonstrated twice in August 1945. A nuclear explosion is horrendously powerful, destroying and killing by means of blast wave, wind, heat, fire, and radiation. Radiation also contaminates food and water. A nuclear war would cause tons of dust to be thrown into the air, blocking sunlight and causing global temperatures to plummet. Food crops and other plants would die. Without food to eat, humans and animals would die of starvation. Some nine countries are said to have the capacity to launch nuclear attacks. A few other nations appear to be in the process of developing their own nuclear weapons. And terrorist organizations are only too eager to get hold of them.

“Nuclear weapons remain the gravest and most immediate threat to human civilization. . . . There are still some 25,000 nuclear weapons worldwide . . . Eventually, terrorists will get the bomb.”​—Union of Concerned Scientists.