Hundreds of millions of Americans are presently besieged by a massive arctic blast and winter storm. Luckily for them, it will only be temporary. That wasn't the case 20,000 years ago...
Between 26,500 to around 19,000 years ago, gargantuan glaciers covered around a quarter of Earth's land area year round. Their frigid reach extended to the areas that are now Minneapolis, Chicago, Detroit, and Boston. The average global temperature was then about 46 degrees Fahrenheit (8 degrees Celsius), 11 degrees F (6 degrees C) cooler than the global annual average today. It was a chilly time to be alive.
And make no mistake, humans were alive. Though much of our species sheltered around the equator at the time, some did live in cooler regions such as central Europe, not far from the glaciers' icy reach. Clothing, constructed dwellings, fire, and omnivory all helped our ancestors outlast the cold.
When that great freeze ended and the ice retreated about 11,700 years ago, then humanity really started to thrive. Buoyed by the warmth of the current "interglacial" period, humans have been able to propagate pretty much everywhere on the surface of Earth.
But what if this period of relative warmth we've enjoyed were to come to an end? What if Earth entered another "ice age"?
First off, Earth is technically in an ice age right now, defined as a time when both of the planet's poles are covered with ice. What people actually mean when they talk about an "ice age" is a "glacial period." This is when the ice at the poles creeps toward the equator. These glaciers reflect the sun’s rays back into space, making the Earth colder, which allows the glaciers to spread further, which chills the Earth even more – a positive feedback loop.
Glacial periods are initially triggered by subtle changes in Earth's orbit as well as its tilt and wobble. These factors collectively affect how much solar radiation the Earth receives. Such changes are cyclic and predictable, which means that we have the ability to gauge when another glacial period is on the way. So when will that be?
Current estimates suggest that we have at least 10,000 more years of relative warmth, and perhaps as many as 200,000. Why the wide range? Because we are ourselves drastically altering the climate by burning fossil fuels. The more we burn, the longer we delay the next glacial period.
In a study published in December, a team of researchers estimated that under current conditions, the next ice age is expected 50,000 years into the future. If we emit twice as much carbon as we have so far, which we're on pace to do in the next five decades, the next ice age will begin in 100,000 years. The researchers say we could delay glaciation by up to 200,000 years from present, but by then an ice age is likely unavoidable.
Professor Andreas Born at the University of Bergen’s Department of Earth Science isn't so sure.
“If a new ice age were to come, cities like Oslo, Stockholm, and Chicago would be covered by several thousand metres of ice. In that case, it's probably highly unlikely that humans would allow this to happen again, as long as there's a society,” he told ScienceNorway. "That could mean that the last ice age was actually the last ice age.”
Over the next tens of thousands of years, it's reasonable to assume that humanity will have pioneered numerous ways to geoengineer the planet's climate on rapid timescales, so another ice age could very well be preventable. But if not, humans will likely have hundreds or even thousands of years to adapt as polar ice returns to claim the land at lower latitudes. It won't appear as suddenly as America's current cold snap.
