The seven biggest threats to humanity revealed: From a nuclear winter to a devastating supervolcano, experts explain the violent ways the world could end

  • How It Works magazine has summarised seven devastating scenarios that could result in the end of the world 
  • They include an asteroid smashing into Earth, a nuclear winter, global pandemic and the sun dying
  • The most probable is the eruption of a supervolcano and a super-eruption is said to occur once every 100,000 years

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The apocalypse may be a popular subject of sci-fi films, but there are some very real scientific theories in danger of becoming reality.

These include being blown to smithereens as an asteroid smashes into Earth and a highly infectious pandemic that wipes out huge swathes of the global population within days. 

However, the most probable is the eruption of a supervolcano, according to a feature in How It Works magazine, which details seven of the most devastating scenarios and threats facing mankind. 

The apocalypse may be a popular subject of sci-fi films, but there are some very real scientific theories that are in danger of becoming reality. The most probable is the eruption of a supervolcano - a thousand times larger than the 1980 Mount Saint Helens eruption – the most destructive volcanic eruption in recorded US history (a stock image is shown)

The apocalypse may be a popular subject of sci-fi films, but there are some very real scientific theories that are in danger of becoming reality. The most probable is the eruption of a supervolcano - a thousand times larger than the 1980 Mount Saint Helens eruption – the most destructive volcanic eruption in recorded US history (a stock image is shown)

A SUPERVOLCANO BLOWS

Supervolcanoes are the leviathans of volcanism. 

Defined by their ability to blast more than 240 cubic miles (1,000 cubic kilometres) of material into the air, they are a thousand times larger than the 1980 Mount Saint Helens eruption – the most destructive volcanic eruption in recorded US history.

MOUNT SAINT HELENS ERUPTION 

The earthquake took place in the morning of 18 May, 1980. 

It created a large landslide that exposed the partly molten rock in the volcano to lower pressures. 

This caused an explosion that sent hot lava and rock 80,000ft (24,385 metres) into the air.

It deposited ash across 11 American states and caused snow, ice and glaciers on the volcano to melt. 

Around 57 people were killed directly. 

Geologists have never witnessed a supervolcanic eruption, but by looking at remnants of previous cataclysms, they can piece together alarming details. 

These eruptions could rain debris and fiery destruction on a geographical region as large as Europe, but it would be the gases they inject into the stratosphere that could spell disaster for humanity.

During a super-eruption, a scalding plume of gas would belch almost to the edge of space. 

Levelling off, it would spread out around the globe, forming a veil of sulphate aerosols that would persist for several years and trigger a volcanic winter.

The veil would reflect and absorb incoming solar radiation, warming the upper atmosphere and preventing heat from reaching the surface. 

The result would be extreme instability in the climate system. 

Surface temperatures would tumble rapidly, leading to agricultural collapse and famine and some even speculate these conditions could lead to the onset of an Ice Age.

Thankfully, such catastrophic super-eruptions are rare. 

The last we know of occurred 27,000 years ago in New Zealand. 

But they are inevitable and critically, we have no idea when the next one will strike and absolutely no way to prevent it. 

Scientists warn a supervolcano eruption could cause a volcanic winter (illustrated). These eruptions rain debris and fiery destruction on a geographical region as large as Europe, but it’s the gases they inject into the stratosphere that could spell disaster for humanity

Scientists warn a supervolcano eruption could cause a volcanic winter (illustrated). These eruptions rain debris and fiery destruction on a geographical region as large as Europe, but it's the gases they inject into the stratosphere that could spell disaster for humanity

How It Work magazine (shown) details seven apocalyptic scenarios

How It Work magazine (shown) details seven apocalyptic scenarios


NUCLEAR WINTER 

With the power to demolish entire cities in seconds, nuclear bombs are the most devastating weapons on the planet. 

In many ways, the people annihilated in the first moments of a blast could be considered the lucky ones.

In the 1980s, prominent scientists including Carl Sagan warned that a nuclear war between the US and the Soviet Union could drive the globe into a catastrophic nuclear winter. 

Incinerated cities and forests would send heaving clouds of sun-blocking ash into the stratosphere and it could take years for particles to be rained out.

In a worst-case scenario, it is predicted that 99 per cent of the sun's light would be blocked for several months, resulting in noon-time twilight and the halting of photosynthesis, meaning food could become scarce.

Surface temperatures could additionally plummet tens of degrees below normal levels for years or even decades, bringing crippling arctic conditions to the entire globe. 

Plants, animals and humans would then perish in the darkness. 

ASTEROID IMPACT

Asteroids are hunks of rocky space debris, left over from the creation of the planets, which whizz around our solar system, orbiting the sun. 

From time to time they cross paths with us and, while impacts on the scale of the infamous 6.2-mile (10km) 'dinosaur-destroyer' are rare, an asteroid a fifth the size could spell disaster for civilisation.

With energy greater than 10 million Hiroshima bombs, the impact shock would flatten everything within a 186-mile (300km) radius. 

Dust and debris would cause an 'impact winter' and most living things would perish. 

Alternatively, an ocean strike would trigger monumental tsunamis, obliterate entire coastlines and inject seawater into the atmosphere, destroying huge swathes of the ozone layer and exposing survivors to devastating levels of UV radiation. 

RUNAWAY GREENHOUSE EFFECT

The greenhouse effect is essential to life as we know it. 

Just like a glass greenhouse lets in light but traps heat, insulating gases in our atmosphere protect us from the deathly cold of space.

But since the Industrial Revolution, humans have been blamed for upsetting the delicate balance of the atmosphere.

Concentrations of carbon dioxide, released when fossil fuels are burned, as well as other 'greenhouse gases', have risen at an alarming rate, forming a thick blanket around Earth, trapping excess heat and nudging global temperatures upwards.

While warmer weather might be welcome in some places, 'feedback loops' complicate the effects of higher temperatures. 

In a worst-case scenario of a nuclear winter, it is predicted that 99 per cent of the sun's light would be blocked for several months, resulting in noontime twilight and the halting of photosynthesis, meaning food could become scarce. This file image shows a mushroom cloud during an atomic weapons test in the 1950s

In a worst-case scenario of a nuclear winter, it is predicted that 99 per cent of the sun's light would be blocked for several months, resulting in noontime twilight and the halting of photosynthesis, meaning food could become scarce. This file image shows a mushroom cloud during an atomic weapons test in the 1950s

In the 1980s, prominent scientists including Carl Sagan warned that a nuclear war between the US and the Soviet Union could drive the globe into a catastrophic nuclear winter (illustrated above)

In the 1980s, prominent scientists including Carl Sagan warned that a nuclear war between the US and the Soviet Union could drive the globe into a catastrophic nuclear winter (illustrated above)

Increased evaporation will cause denser cloud cover, exacerbating the warming effect because clouds themselves are strong insulators. 

Longstanding carbon 'sinks' - rocks and oceans that pull carbon dioxide out of the atmosphere - are predicted to become unstable and release their stores, accelerating the problem still further.

Scientists warn of a tipping point – a temperature beyond which the problem can no longer be dialled back. 

If we reach this point, a runaway greenhouse effect would cause temperatures to soar to several hundred degrees Celsius, boiling the oceans and making life on Earth impossible. 

From time to time they cross paths with us and, while impacts on the scale of the infamous 6.2-mile (10km) dinosaur-destroyer are rare, an asteroid a fifth the size could spell disaster for civilisation. Options of how to tackle the scenario are discussed above

From time to time they cross paths with us and, while impacts on the scale of the infamous 6.2-mile (10km) dinosaur-destroyer are rare, an asteroid a fifth the size could spell disaster for civilisation. Options of how to tackle the scenario are discussed above

THE DEATH OF THE SUN 

The sun supplies the energy for almost all of life on Earth, but all good things come to an end. 

When the sun's time comes and it starts to run out of fuel, its core will collapse as the outward force – due to fusion – can no longer balance the strong inward force of gravity. 

At the same time, its outer envelope will inflate, expanding the star into a red giant, and engulfing the orbits of Mercury, Venus, and potentially, Earth.

Eventually, the dying sun will transform into a dense white dwarf surrounded by a dazzling planetary nebula. 

Humans won't be around to see this; the sun's fuel supply will start to run low about five billion years from now, but Earth will be inhospitable long before. 

Since the Industrial Revolution, humans have upset the delicate balance of the atmosphere. Concentrations of carbon dioxide, released when fossil fuels are burned, as well as other ‘greenhouse gases’, have risen at an alarming rate, forming a thick blanket around Earth, trapping excess heat and nudging global temperatures upwards. The possible consequences are illustrated above

Since the Industrial Revolution, humans have upset the delicate balance of the atmosphere. Concentrations of carbon dioxide, released when fossil fuels are burned, as well as other 'greenhouse gases', have risen at an alarming rate, forming a thick blanket around Earth, trapping excess heat and nudging global temperatures upwards. The possible consequences are illustrated above

GAMMA-RAY BURST 

Gamma-ray bursts (GRBs) are the brightest events in the universe. 

Produced by the explosion of massive stars, they emit focused beams of intense gamma radiation. 

They can last anywhere from a fraction of a second to several hours, and can release as much energy in ten seconds as the Sun will produce in its entire lifetime.

If the Earth were unlucky enough to get caught in a GRB's almighty death beam, the effects would be catastrophic. 

It would trigger atmospheric chemistry that would destroy the ozone layer – leaving life on the surface exposed to deadly ultraviolet radiation. 

When the sun’s time comes and it starts to run out of fuel, its core will collapse as the outward force – due to fusion – can no longer balance the strong inward force of gravity. At the same time, its outer envelope will inflate, expanding the star into a red giant, and engulfing the orbits of Mercury, Venus and – potentially – Earth. A fictional view from Earth

When the sun's time comes and it starts to run out of fuel, its core will collapse as the outward force – due to fusion – can no longer balance the strong inward force of gravity. At the same time, its outer envelope will inflate, expanding the star into a red giant, and engulfing the orbits of Mercury, Venus and – potentially – Earth. A fictional view from Earth

GLOBAL PANDEMIC

A pandemic is an outbreak of infectious disease that spreads throughout much of the globe. 

Human history is punctuated by debilitating pandemics and, despite medical advances, it's only a matter of time before we see another.

Today's standards of sanitation and medical research help us stay one step ahead of most infectious agents, but widespread international travel and increased population densities make it much easier for a global pandemic to threaten us all.

In 2003, Sars (severe acute respiratory syndrome) – a serious form of pneumonia – spread to six of the world's seven continents within months, infecting an estimated 8,000 people and killing 750. 

More recently, Ebola – a grisly disease ravaging West Africa with a death toll over 11,000 – threatened to go pandemic in late 2014 after cases seen in travellers arriving back in North America and Europe.

Emerging diseases pose the biggest problem, since they involve unknown pathogens with no existing vaccinations. 

The most dangerous are highly contagious but have delayed symptom onset, meaning that infected people unwittingly spread the disease to many others before realising they are sick. 

Shape-shifting diseases that mutate fast are almost impossible to vaccinate against. In today's hyper-mobile, city-dominated world, a deadly disease combining these three features could spell doom for the human race.

Gamma-ray bursts (GRBs) are the brightest events in the universe. Produced by the explosion of massive stars, they emit focused beams of intense gamma radiation. Their anatomy is described in the infographic above. If the Earth were unlucky enough to get caught in a GRB's almighty death beam, the effects would be catastrophic

Gamma-ray bursts (GRBs) are the brightest events in the universe. Produced by the explosion of massive stars, they emit focused beams of intense gamma radiation. Their anatomy is described in the infographic above. If the Earth were unlucky enough to get caught in a GRB's almighty death beam, the effects would be catastrophic

As to which of these doomsday scenarios will become a world-ending reality, it is anyone's guess.

Optimists would assure you that humanity will avoid foolish nuclear wars, begin to behave responsibly in response to climate change, and stay one step ahead of emerging diseases. 

These things, at least, are feasibly within our control. Beyond that, we are at the mercy of the laws of physics 

Recently, Ebola – a grisly disease ravaging West Africa with a death toll over 11,000 – threatened to go pandemic in late 2014 after cases seen in travellers arriving back in North America and Europe. This artificially-coloured microscope image shows Ebola virus particles in blue, budding from a chronically-infected cell

Recently, Ebola – a grisly disease ravaging West Africa with a death toll over 11,000 – threatened to go pandemic in late 2014 after cases seen in travellers arriving back in North America and Europe. This artificially-coloured microscope image shows Ebola virus particles in blue, budding from a chronically-infected cell

A pandemic is an outbreak of infectious disease that spreads throughout much of the globe. Human history is punctuated by debilitating pandemics and, despite medical advances, it’s only a matter of time before we see another. The deadliest in history are shown above

A pandemic is an outbreak of infectious disease that spreads throughout much of the globe. Human history is punctuated by debilitating pandemics and, despite medical advances, it's only a matter of time before we see another. The deadliest in history are shown above

Statistically, a supervolcano is most likely to hit first. 

A devastating super-eruption is thought to occur about once every 100,000 years, whereas world-threatening GRBs and asteroids rear their heads perhaps only once in every 500,000.

In truth, it's likely that a combination of catastrophic events - and a chaotic human response to them - will secure our demise. If they don't – the Sun will be hot on our heels in a billion years' time.

WHAT CAUSED THE MASS EXTINCTION OF THE DINOSAURS? THE LEADING THEORIES

ASTEROID

It is generally accepted the dinosaurs became extinct, or were helped on their way to extinction, when a meteor smashed into Earth between 65 and 66 million years ago.

The impact on the Yucatán Peninsula in Mexico created a crater six miles (10km) wide, throwing up enough debris into the atmosphere to block out sunlight.

This prevented plants from growing, causing herbivores to starve and depriving predators such as T-rex of a meal too when their food became scarce.

VOLCANOES

However, some experts believe the impact is a red herring and the real reason for the mass extinction was a surge of volcanic activity in a region of India known as the Deccan Traps.

Experts at the University of California at Berkeley believe it was a combination of the meteor impact followed by a volcanic storm.

This is because the meteor collision shook up the Earth so much that it turned up the volcanic heat.

Within 50,000 years of the impact, the Deccan Traps volcanoes doubled their output, blanketing the Earth with sulphurous gas and dust.

Together, the impact and volcanism caused a dramatic change in climate as the sun's rays were blanketed out in a version of the 'nuclear winter' predicted to follow a global nuclear war.

It is generally accepted the dinosaurs became extinct, or were helped on their way to extinction, when a meteor smashed into Earth between 65 and 66 million years ago. The impact on the Yucatán Peninsula in Mexico created a crater six miles (10km) wide, throwing up enough debris into the atmosphere to block out sunlight (artist's impression)

It is generally accepted the dinosaurs became extinct, or were helped on their way to extinction, when a meteor smashed into Earth between 65 and 66 million years ago. The impact on the Yucatán Peninsula in Mexico created a crater six miles (10km) wide, throwing up enough debris into the atmosphere to block out sunlight (artist's impression)

BAD LUCK

Last year, a study claimed the majority of the prehistoric creatures were wiped out by a perfect storm of 'colossal bad luck'.

Dinosaurs might have survived the asteroid strike that led to their extinction if it had come slightly earlier or later in history, scientists said.

But when the asteroid hit, dinosaurs were experiencing environmental upheaval, which left them vulnerable.

The study by an international team of palaeontologists led by the University of Edinburgh looked at an updated catalogue of dinosaur fossils, mostly from North America.

They found that widespread volcanic activity, changing sea levels and varying temperatures had weakened the dinosaurs' food chain when disaster struck.

If the asteroid impact had come a few million years earlier, when the range of species was bigger and food chains more robust, they may have survived, according to the study.

Whatever the reason for the prehistoric beasts' extinction, a 2014 study argued the mass extinction event took 33,000 years in total, but estimates have been a wild as 300,000 years.

 

 

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