Medium-Sized Asteroid Impact Would Darken The Sky And Freeze The World

Where's Bruce Willis when you need him? solarseven/Shutterstock

A new study, presented at last December’s American Geophysical Union, has revealed that a strike by a medium-sized asteroid is almost certain to suddenly alter Earth’s climate, causing the planet to become dry, frigid, and shrouded in darkness. It is clear that in a post-impact world, life would be incredibly difficult for many.

The asteroid impact that famously heralded the end of the age of the dinosaurs didn’t wipe them out in one fell swoop. The impact itself caused a major change in the planet’s climate, with the uplifted dust blanketing the atmosphere, blocking out massive amounts of sunlight. This not only caused sudden global cooling, but the photosynthesis of plants stalled worldwide, causing a catastrophic food chain collapse – all of which slowly killed off the Tyrannosaurs and their cousins.

This cataclysm-causing asteroid was roughly 10 kilometers (6 miles) wide; its climate-changing effects were only lessened by the fact that it impacted the ocean, not the land. Unfortunately, this new study, which used sophisticated computer simulations, reveals that even a 1 kilometer-wide (0.6 miles) asteroid would still produce similarly devastating effects if it hit a continental land mass.

Firstly, the immense kinetic energy of the asteroid would carve out a crater 15 kilometers (9 miles) wide, which would throw vast amounts of material into the air. Depending on the density of the material, and how pulverized the source rock would be upon impact, impact-generated dust and soot would cause the skies to darken for around six to 10 years. If the fireball generated by the initial impact caused widespread, long-lasting fires, very buoyant soot could be continually generated and lifted into the atmosphere, fueling the production of a prolonged dark sky.

Wildfires would likely engulf the globe. Tom Reichner/Shutterstock

In a worst-case scenario, the skies would dim by a remarkable 70 percent for the first year or two, cooling surface temperatures by an average of 8°C (14.5°F), which would bring Earth into an abrupt ice age climate state. This cooling will also disrupt precipitation levels: With lower surface temperatures, there will be lower evaporation rates of surface water.

Consequently, there will be less atmospheric water to rain down on the world post-impact – 20 percent less for the first six years, according to the study. This will make our apocalyptically cold world considerably drier. With less rain and darkened skies, plant growth and photosynthesis rates will almost certainly plummet, and a food chain collapse will become inevitable.

The soot and dust particles will not only cause the planet to cool – they will absorb incoming solar radiation, heat up in the upper atmosphere, and speed up chemical reactions that destroy the ozone layer that protects the planet from harmful ultraviolet (UV) radiation. Current U.S. Environmental Protection Agency guidelines note that a UV index of 11 means that standing exposed to the sun will cause your skin extreme harm. Post-impact, the surface UV index near the tropics will be topping 20.

“These would not be pleasant times,” opined Charles Bardeen, lead author of the study, as reported by Space.com. There is some good news, though: This medium-sized asteroid wouldn’t cause a mass extinction – that would require a rock roughly the size of the asteroid that killed the dinosaurs. Even if a 1-kilometer-wide asteroid was heading towards us, we'd have some time to prepare, as these only impact Earth roughly once every 500,000 years.

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