What's the biggest threat to the future of humanity right now? Will our robot overlords finally turn on us, or will the hate speech used by certain world leaders incite us to become murderous hordes and we'll just take each other out? In its annual report on global risks, Swedish non-profit Global Challenges Foundation has announced the nine most likely ways humanity could be wiped out.

The Global Catastrophic Risks report is based on scientific research and contributions from leading academic experts to “create a deeper understanding of catastrophic risk, and thereby to spark a discussion of how the management of such risks can be developed and improved.”

“We fret about familiar risks – air crashes, carcinogens in food, low radiation, etc. – and they’re all intensely studied,” wrote Martin Rees, UK Astronomer Royal and co-founder of Cambridge’s Center for the Study of Existential Risk. “But we’re in denial about some emergent threats – the potential downsides of fast-developing new technologies and the risk of crossing environmental ‘tipping points.’”

Though improbable, the following scenarios could have global consequences.

Nuclear Warfare

Although the probability of global nuclear warfare is estimated to be no more than 1 percent, even one detonation could kill as much as 95 percent of the people within a 4-kilometer radius of detonation with very severe damage extending six times as far.

Russia and the US are home to the world’s largest arsenals, each with about 7,000 warheads, with the UK, France, China, India, Pakistan, North Korea, and Israel also housing nukes. According to one scenario, an “all-out exchange” of 4,000 nuclear weapons would not only result in an enormous loss of lives, but would release 150 teragrams of smoke, leading to an 8°C drop in global temperature for up to five years, at which point “most of the surviving world population would die from hunger”.

Biological And Chemical Warfare

Unlike nuclear, biological and chemical weapons can be developed at a relatively low cost and distributed in a variety of ways throughout entire regions, releasing pathogens worldwide that could result in pandemics, whether through accidental or intentional release. 

Catastrophic Climate Change

Current efforts aim at mitigating low- to mid-range scenarios with a temperature increase of up to 2°C, but there is potential for a “tail end” risk for an even greater increase. Even a less than 2°C rise would intensify and make tropical cyclones more frequent, collapse entire ecosystems, deteriorate agricultural land, lose reliably freshwater sources, and push major coastal cities under water, relocating more than 1 billion people.

Ecological Collapse

Pushing ecosystems beyond their tipping point could diminish biodiversity and freshwater supplies, cause agricultural capacity to plummet, and drastically deteriorate our daily living conditions. 

Pandemics

Though very rare, the global spread of disease can be extremely lethal and is made all the easier given our ability to transverse continents in a matter of hours. A pandemic’s risk is determined by the pathogen’s virulence, infection risk, and incubation period.

Asteroid Impact

Though it’s unlikely that an asteroid big enough to cause a fourth mass extinction exists within Earth’s orbit, it’s not impossible. If an asteroid similar in size (about 1 kilometer) to the dinosaur-killing one 65 million years ago, its impact would eject enough particles into the atmosphere to dim the Sun for several months, cooling the planet and undermining ecosystems.

Supervolcanic Eruption

Currently, we unable to anticipate volcanic eruptions beyond a few months in advance but scientists are avidly monitoring potential supervolcanoes, such as Yellowstone’s caldera. If such an eruption were to occur, dust and sulfates would be ejected into the atmosphere, causing the climate to cool by about 3-5°C over several years.

Solar Engineering

This technology reflects light and heat from the Sun back into space using aerosols or other particles in order to cool the planet, yet we don’t really understand the risks or potential benefits. It has the potential to destabilize local and global climates or, if suddenly terminated, resulting in “rapid and severe global warming.”

Artificial Intelligence

Superintelligent AI in the wrong hands sounds like the premise of an Austin Powers revamp, but it could result in a number of devastating consequences as non-biological intelligence could be used to accomplish complex goals that are not always in line with the needs of humanity.