Scientists who research Earth’s deep past have uncovered bounties and bounties and bounties of evidence that the planet’s climate has changed repeatedly and dramatically.
But nothing compares to what's happening today.
The primary lever controlling Earth's temperature is the amount of carbon dioxide in the atmosphere, which has naturally fluctuated over time. Rises and drops in CO2 have mirrored rises and drops in temperature, leading to the advance and retreat of colossal glaciers over the continents. (In recent geological time, an ice sheet covered modern-day Manhattan.) For some 11,000 years now, Earth has been in a relatively warmer period, a deglaciated time called an "interglacial." The great glaciers have retreated; human civilization has flourished.
Yet the heating today, largely driven by the burning of carbon-rich fossil fuels, is now accelerating into unprecedented, and deeply problematic, territory. During an interglacial period, CO2 levels rise gradually, often allowing life to adapt. But today, CO2 levels are skyrocketing. The system is out of control. This is depicted in the graph below, created by Kristopher Karnauskas, an associate professor in the Department of Atmospheric and Oceanic Sciences at the University of Colorado Boulder.
"Right now, CO2 levels are rising over 200 times faster than they did during the last deglaciation," Karnauskas told Mashable. "That number speaks to the urgency to act soon." (Here's an example of robust action to slash heat-trapping carbon emissions.)
Take a look. The nearly vertical red line is the carbon dioxide rise (after already naturally rising during the current interglacial period) since the start of the Industrial Revolution:
In other words, what's occurring in Earth's atmosphere today is geologically unprecedented.
Today, fossil fuel giants are mechanically removing ancient, decomposed remains of dead organisms from the ground (oil, gas, and coal), and then these carbon-rich fuels are burned, with emissions going straight into the air. It's a very direct, efficient way to heat a planet.
Without these human activities, carbon dioxide levels in the atmosphere would naturally be below 300 parts per million, or ppm, like they have for at least some 800,000 years, explained Murat Aydin, a research scientist at the University of California, Irvine, who researches atmospheric gases.
But now we're well over 400 ppm, and relentlessly rising. "That's really big," Aydin told Mashable. "That's a really big pulse in the atmosphere."
Update April 20, 2023: Earth's atmospheric CO2 levels averaged over 417 ppm in 2022, and even recently reached a daily reading of over 424 ppm.
There's no doubt today's CO2 levels are profoundly out of whack. Researchers like Aydin have a firm grasp on the atmosphere's past carbon dioxide concentrations. The strongest evidence lies in ice cores drilled deep from Antarctic ice. Hundreds of thousands of years ago, when precipitation fell on the Antarctic ground, the water froze into ice, which also sealed off pockets of air. Ultimately, thousands of feet of ice amassed atop these bubbles, preserving the ancient atmosphere.
"It's literally a sample of the atmosphere from a long time ago," Aydin said.
The many problems with Earth's rapid heating
Yes, Earth has experienced many bouts of cooler and warmer climes, resulting in glacial and interglacial periods. But skyrocketing CO2 levels have already heated Earth by nearly 2 degrees Fahrenheit since just the late 19th century. More warming is inevitable — though, critically, how much more is a product of how much carbon humanity emits into the atmosphere. There are known, deployable ways to slash vast amounts of carbon emissions, like building ocean wind farms to produce energy.
The consequences of such fast, abnormal warming are already driving severe and significant change. Today's heating:
makes intense wildfires more frequent, because a warmer atmosphere dries out vegetation and trees, which more easily burn. ("It takes just a little bit of warming to lead to a lot more burning.")
melts some of Earth's largest ice sheets, like on Greenland. This raises sea levels, and will contribute to sea level rise for centuries.
makes marine heat waves — which cause major coral die-offs — more frequent and extreme. Marine biologists expect marine heat waves this century to have "significant" and "widespread" ecological impacts, like on the fish that depend on coral ecosystems.
makes droughts more severe, like the prolonged Southwestern megadrought. Historically, droughts have significantly decreased crop yields.
increases the odds for more extreme downpours and floods, because a warmer atmosphere can hold more water vapor.
creates warmer ocean temperatures which are jet fuel for hurricanes. Though hurricane development hinges on a number of complex weather factors, and the science of hurricane intensification is still unfolding, the U.S. National Oceanic and Atmospheric Administration expects cyclone intensities to increase in a world warmed by 3.6 F (2 C).
Modern, and still rising, CO2 levels may take us into some unsettling global terrain. During the last interglacial period, some 125,000 to 118,000 years ago, vast amounts of ice melted on Antarctica, resulting in a whopping six to nine meters of sea level rise. This happened gradually, over thousands of years.
But as CO2 enters unchartered territory, climate scientists are carefully observing an ongoing acceleration in sea level rise, and assessing what it might mean for the billions of coastal dwellers in the decades, and centuries, ahead. Already, sea levels around the U.S. are expected to rise by a foot or so in just the next 30 years. That's rapid change.
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"The rates of change are what's concerning," Daniel Gavin, a biogeographer at the University of Oregon, told Mashable.
During past interglacial periods, glacier scientists have evidence that the ice sheet on Baffin Island — a frigid Arctic land in Northern Canada — rarely melted away. Now, they're watching it shrink each year, and suspect it will totally disappear in a few hundred years.
"The last remnants of ice on Baffin Island are going away now," said Gavin.
This story was originally published in April 2022 and has been updated.
