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10 ways the world is most likely to end, explained by scientists

An asteroid got the dinosaurs. Here’s what’s most likely to kill us.

Anti North Korea Protest Continues In Seoul
South Korean conservative protesters participate in a rally a day after North Korea announced it had conducted a third nuclear test on February 13, 2013, in Seoul. 
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Remember when the possibility of nuclear war seemed remote? The fact that it doesn’t anymore shows how quickly threats to humanity can change and how important they are to pay attention to.

The Global Challenges Foundation, which works to reduce the global problems that threaten humanity, compiles an annual report on global catastrophic risks. The group released the 2018 edition in September, and the litany is harrowing: Chemical warfare, supervolcanic eruptions, asteroid collisions, and the looming effects of climate change threaten to cause everything from civilizational collapse to human extinction.

Some of these risks sound like science fiction, but so did weapons of mass destruction and climate change 100 years ago. As Allan Dafoe and Anders Sandberg of the Future of Humanity Institute write, our brains aren’t good at thinking about catastrophic risk because they either “completely neglect or massively overweight” things that are low probability. So the report, overseen by a team at GCF but with each section written by leading experts, combines historical evidence and scientific data to determine the biggest threats.

The good news for us is that scientists think the world will be habitable for at least a few hundred million more years. The bad news is there’s a lot that could change that. The risk of the threats highlighted in the report actually causing mass casualties are still small, but that doesn’t mean they’re not important to pay attention to — especially when the worst-case scenario means human extinction.

Here’s what should be keeping you up at night and what, realistically, might cause humans to go the way of dinosaurs.

1) Nuclear war

A nuclear detonation from one of today’s more powerful weapons would cause a fatality rate of 80 to 95 percent in the blast zone stretching out to a radius of 4 kilometers — although “severe damage” could reach six times as far.

But it isn’t just the immediate deaths we need to worry about — it’s the nuclear winter. This is when the clouds of dust and smoke released shroud the planet and block out the sun, causing temperatures to drop, possibly for years. If 4,000 nuclear weapons were detonated — a possibility in the event of all-out nuclear war between the US and Russia, which hold the vast majority of the world’s stockpile — an untold number of people would be killed, and temperatures could drop by 8 degrees Celsius over four to five years. Humans wouldn’t be able to grow food; chaos and violence would ensue.

A big worry here is the arsenal of nukes. While numbers have fallen over several decades, the United States and Russia have just under 7,000 warheads each, the largest collections in the world. The UK, France, China, India, Pakistan, North Korea, and Israel all have nuclear weapons.

Hundreds of nuclear weapons are ready to be released within minutes, a troubling fact considering that the biggest threat of nuclear war may be an accident or miscommunication. A few times since the 1960s, Russian officers (and, in 1995, the president) narrowly decided not to launch a nuclear weapon in response to what they’d later find out were false alarms.

2) Biological and chemical warfare

Unlike nuclear weapons, which require complex engineering, biological and chemical warfare can be developed at a relatively low cost and with relatively attainable materials.

In the past few years, the Syrian government has used chemical weapons in the civil war that has ravaged the country. These chemical attacks using sarin and chlorine have appalled the international community, and underscored the damage chemical weapons can do. Weaponized toxic chemicals could do tremendous harm to a localized target — say, if the toxins were released into the air or into the water supply.

Biological weapons represent a greater catastrophic threat. Advances in synthetic biology have made very real the possibility of malicious actors creating harmful pathogens for weaponization — or innocent researchers accidentally releasing a lethal infectious bug out into the world. In the event of a fast-moving pandemic, the world would be pretty vulnerable.

3) Catastrophic climate change

A United Nations panel of scientists released a report last week saying that we only have 12 years to keep global warming to moderate levels.

Projections of the effects of climate change vary depending on how much the Earth warms (usually modeled on an increase of 1 to 3 degree Celsius). None of the scenarios look good.

At best, we’re looking at more frequent and severe tropical cyclones. Midrange predictions include the loss of the majority of global agricultural land and freshwater sources, with major coastal cities like New York and Mumbai ending up underwater. At worst, human civilization would come to an end.

Even if current global commitments to reduce carbon emissions are kept, there is a one-third chance of the Earth’s temperature increasing by 3°C, which would cause most of Florida and Bangladesh to drown.

Catastrophic climate change is also not something we’re dedicating nearly enough attention to. The author of this section in the report, Dr. Leena Srivastava, the acting director of general at the Energy and Resources Institute, points out that we’ve put enough time and resources into airplane safety that only 27 planes crash a year. But “if dying in a flight accident was as likely as a 3°C global temperature increase, then the number of people dying in airplanes every year would be 15 [million].”

4) Ecological collapse

Salton Sea Plan Calls For 200,000 Homes On Former Atomic Weapons Site
A tree killed by rising saltwater is seen beyond a mud flat at dawn on the east shore of the Salton Sea on October 22, 2005. across the lake from Salton City, California.
David McNew/Getty Images

Ecosystems are the delicate community of living organisms, like humans and animals, interacting with their nonliving environment, like air and water. Ecosystems can recover from a certain amount of impact from humans, like temperature increases or habitat loss, but there’s a tipping point at which they can’t — and according to the report, we might be reaching that tipping point.

Lake Chad in West Africa is an example of ecological collapse. Sixty years of drought, overuse of water, and the impacts of climate change have reduced the lake by 90 percent. Its massive reduction has adversely affected the livelihoods of more than 40 million people in Chad, Nigeria, Niger, and Cameroon that depend on it.

Scholars believe this moment in history constitutes a new geological era, called the Anthropocene. In this new era, humans are the primary change agents, rapidly degrading what makes the planet habitable, intensifying greenhouse gas concentration, and damaging the health of marine ecosystems.

5) Pandemics

Twice in modern history, plagues have swept across the world, killing an estimated 15 percent of the population in a few decades. They occurred way back in the fifth and 14th centuries, respectivelybut there is a serious risk that a new infectious disease could cause another outbreak, especially with today’s urban and mobile global population.

Luckily, deadly diseases with the capacity to spread globally are rare. But they do happen — a century ago, the Spanish flu killed more than 50 million people. Outbreaks of SARS and Ebola in recent years also ring alarm bells.

Antibiotics, our greatest defense against disease, are becoming less effective as some strains of bacteria become resistant to them. Antibiotic-resistant bacteria are responsible for an estimated 700,000 annual deaths. If we don’t develop new advances against antibiotic resistance, that number is estimated to reach 10 million by 2050.

6) Asteroid impact

Asteroids are rocks that revolve around the sun and that occasionally collide with the Earth. An asteroid large enough to cause a global catastrophe hits Earth every 120,000 years, scientists estimate. It’s likely what killed the dinosaurs, and if an asteroid even one-tenth the size of the one that caused their extinction hit Earth today, the results would be devastating. Scientists estimate it could release enough particles to block the sun for months and cause a famine killing hundreds of millions.

NASA announced in 2011 that it had mapped more than 90 percent of objects in space larger than 1 kilometer in diameter, and that none of them are likely to hit Earth. But there’s still a lot we don’t know about smaller objects that, while unlikely to cause a global catastrophe, could have a big enough local impact to disrupt social and economic systems.

7) Supervolcanic eruption

Hawaii’s Kilauea Volcano Erupts Forcing Evacuations
Onlookers and media gather as lava from a Kilauea volcano fissure erupts in Leilani Estates, on Hawaii’s Big Island, on May 26, 2018.
Mario Tama/Getty Images

A supervolcanic explosion 74,000 years ago ejected so much debris into the atmosphere that scientists believe it caused the Earth to cool by several degrees Celsius. Some experts believe this caused the greatest mass plant and animal extinction in human history, bringing the species to the brink of extinction.

How likely is that to happen today? It’s hard to say since we don’t have much to compare it to, but data suggests a supervolcanic eruption occurs on average every 17,000 years. If that’s true, then we’re overdue — the last one we know of was 26,500 years ago in New Zealand.

We don’t have a way to anticipate eruptions more than a few weeks or months in advance, and we don’t really have any way to reduce the likelihood of eruption right now, but scientists are monitoring several areas of risk, including Yellowstone in the US.

8) Solar geoengineering

There’s a dramatic option for stopping, or even reversing, rising global temperatures, but it comes with significant possible risk.

Solar geoengineering would reflect light and heat away from Earth and back into space by injecting aerosols into the stratosphere, the second layer of Earth’s atmosphere. For now, it only exists in computer models, but the first experiment is being planned by Harvard researchers.

Solar geoengineering is one of two emerging technologies that could manipulate the atmosphere and reduce climate risk. The other is directly removing carbon dioxide from the atmosphere, which doesn’t currently exist on a big enough scale.

If solar geoengineering were deployed, it would affect the entire atmosphere and be humanity’s largest-ever global endeavor. While it is the only known technique that could stop rising temperatures, there’s still a lot we don’t know, including whether it could destabilize local and global climate or ecosystems. Manipulation on this scale without understanding the effects could turn out to be catastrophic for the human race. The technology could also be cheap enough (as low as $10 billion a year) that it could be wielded by one country or a wealthy individual, introducing the possibility of reckless use.

9) Artificial intelligence

Artificial intelligence (AI) is progressing rapidly. Surveyed scientists estimate, on average, that there is a 50 percent chance of AI being able to perform most tasks as well as, or better than, humans by 2050, with at least a 5 percent chance of surpassing human intelligence a couple of years after that.

There’s a common misconception that the risk of AI is that it will become malevolent. The bigger concern is that it will become too good at its job. As the report says: “If you ask an obedient, intelligent car to take you to the airport as fast as possible, it might get you there chased by helicopters and covered in vomit, doing not what you wanted but literally what you asked for.”

The implications become much more frightening when you consider AI weapons in the hands of the wrong person, or an AI arms race leading to an AI war.

10) Unknown risks

It wasn’t that long ago that climate change and nuclear warfare were largely unheard of. Today, they’re risks we’ve already seen the devastating effects of — and that we worry could get much worse. Because of this, there’s a possibility that we haven’t even conceived of what is most likely to kill us.

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