New research reveals humans halted the Little Ice Age. Is it too late to learn from our mistakes?

by Patrick Doyle | photo by Ethan Welty

In July 1998, Thomas Painter took a break from his doctoral studies on the reflective nature of snow to climb the Maroon Bells near Aspen, Colorado. The snow was unusually filthy along his route. On a whim, he scraped the dirt off a small area with his ice axe and continued climbing. After summiting, Painter returned to the snowfield. The clean patch was now a small, extruded tower; the blackened snow rapidly melting around it. “It was sticking up about three inches—in a day,” says Painter.

Around that time, climate scientists were grappling with a conundrum tied to the end of the Little Ice Age, a period of below-average temperatures in the 16th through 19th centuries. Researchers had pegged the ice age’s demise to 1860, when glaciers in the Alps began to retreat. But that theory didn’t quite compute. Regional temperatures continued to decline for another 60 years. If anything, the glaciers should have kept growing.

Painter wondered if dirty snow could have been at play. In 1860, the Industrial Revolution’s coal-burning factories started spewing soot that covered European cities and—Painter guessed—the glaciers in the Alps. He hunted down ice cores from the Alps and found that layers of black carbon began appearing in the mid-19th century. Like the dirty snow melting on the Maroon Bells, the soot liquefied hundreds of meters of glacier in just 20 years. Painter, now an ice and snow scientist at NASA’s Jet Propulsion Lab, published his findings in September 2013. “I was just in the right place at the right time,” he says. “I was thinking of junk falling on snow.”

The study doesn’t just rewrite the ending of the Earth’s most recent ice age; it underlines the fact that humans caused it. Painter’s work also suggests that black carbon settling on snow runs a close second to carbon dioxide as a driver of global warming. Which means the fall of King Coal in North America is good news for snow and glaciers. Nearly half of U.S. energy came from coal in 2007. By 2012 that number had dropped to 37 percent. Expect that trend to continue, driven by increased consumption of cleaner natural gas and the Obama administration’s tighter emissions regulations for future coal plants. And while China’s coal usage has skyrocketed in recent decades, the country’s coal imports finally began to drop this year due to a slowing economy and pollution levels so high they are poisoning the population.

The switch to cleaner fuels can’t happen soon enough. But in India, a growing economy means increasing demand for coal. And more black carbon on Himalayan snow and glaciers. “What we’re seeing in the Himalaya in terms of glacier retreat is profound,” says Painter.

How it works:

Black carbon from coal-burning power plants blows into the atmosphere and settles on the mountains.

Most of that soot lands on glaciers at lower elevations, which are already susceptible to melting from summer sun.

The darkened snow melts at double the speed of clean snow, causing the glacier to retreat up the mountain.

Smaller glaciers are less able to mitigate the effects of climate change, causing a spiral of increased temperatures and less stable weather.