Earth's climate has slowly fluctuated between cold and hot periods for millions of years. Today, humans are greatly accelerating that process.
How Humans Could Make Icehouse Earth into a Hothouse
Published: March 4, 2020
Ana Aceves: We are on a collision course.
Imagine our climate is a car that has airbags and seatbelts rated to withstand an impact at 60 miles per hour—but instead, we’re driving at 6000 miles per hour. To understand how we got here, first we’ve got to learn how to tell time. But, not the kind of time you can measure on your watch. You need to be able to read climate time.
First, let’s take a look back into deep time. Over the last four and a half billion years, our planet has gone from being a fiery molten planet, to a frozen snowball Earth, to the “just right” planet for us. But when scientists think about climate, they're mostly only talking about the last half a billion years, since that’s when the composition of our atmosphere came to remotely resemble what we have today.
So, what has our planet’s climate been like for the last few hundred million years? Mostly: HOT!
This world looked totally different! Fossils show that about 50 million years ago, the Arctic was a warm humid swamp, with hippo-like animals, turtles, tapir, and even alligators! And about 70 million years ago, Antarctica was covered by forests and filled with dinosaurs!
By piecing together data from fossils and ancient rocks, scientists have built a temperature timeline. It shows that for the last 500 million years, Earth has mostly been in what is called a “Hothouse” – when, unlike today, there are no ice sheets at the poles. But a few times, the planet flipped into an "Icehouse”—when there is ice at at least one of the poles. Like there is today.
Scientists think the planet’s temperature in deep time had something to do with the movement and arrangement of Earth’s tectonic plates. If less carbon dioxide was emitted from the processes associated with plate tectonics—like volcanism—then the Earth would be cool. If more CO2 was emitted, then it would be warm.
And the weathering of rocks and mountains is what removes CO2 from the atmosphere and locks it back underground. This is called the Deep Carbon Cycle—and it moves very slowly, measured in the millions to tens of millions of years.
So, to clock the big swings in our planet’s climate, you need a watch with a “millions of years” hand.
The Hothouse world was three times more common than the Icehouse world. And yet today, there is ice covering both the Arctic, and Antarctica! This means, we are actually in an Icehouse.
Within this Icehouse, there are times when it has gotten even colder than today—the “ice ages,” when ice extended over the northern continents.
If Seattle’s Space Needle were around back then, it would have been covered in almost 3,000 feet of ice! That’s five Space Needles worth of ice.
The smaller changes to our planet’s climate—within our Icehouse, going from really icy to just kinda icy—are caused by changes in Earth’s orbit and the resulting feedback cycles with carbon dioxide in the ocean, biosphere, and atmosphere.
It gets pretty complicated, so we have a whole other video that explains that.
But, the point is: even these changes within our ice house happened over thousands of years. So, you need a “thousands of years” hand on that Climate Watch.
And here’s the problem: Humans have been putting carbon from deep in the Earth into the atmosphere as CO2 way faster than these natural cycles.
In just the last few hundred years, we’ve raised the concentration of CO2 to levels higher than anything the planet’s seen in the last 3 million years.
Climate is being forced into human time. But human time and climate time are totally incompatible.
Our climate has never been so profoundly impacted by a mere mammal that walks on it. A lot of scientists are now saying that humans have become a geological force—and one that acts fast.
If we continue to emit greenhouse gasses at the current rate, the concentration of CO2 in the atmosphere will be that of the Hothouse world within a few hundred years. That's crazy!
That’s a shift happening hundreds to thousands of times faster than is natural. We don’t really know how the planet, and all the life on it, will respond to such a sudden shock.
Digital Producer: Ana Aceves
Producer: Caitlin Saks
Camera: Arlo Pérez
Sound: Madeline Weir
Production Assistance: Angelica Coleman
Special Thanks: David Archer, Kirk Johnson, Charles Langmuir, Isabel P. Montañez
Don Becker, USGS
PhanTASTIC (Phanerozoic Technique-Averaged Surface Temperature Integrated Curve) courtesy of NMNH, Smithsonian
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