“Rain, rain, go away, come again another day …”

Once a well-known children’s song, and now the chorus to a hot new show called Chicago Supercell, which debuted on September 11, 2022 … just kidding! But Chicago did get an unexpected show that day when a sudden storm – dubbed a “supercell” – dumped almost five inches of rain on the city in under two hours.

The city’s sewer system, designed to withstand this “once-in-a-hundred-year flood,” couldn’t hold the deluge. Basements filled with knee-high water. Water submerged streets, turning them into impassable rivers. Geyser-like blasts shot from sewer grates, shutting down roads and businesses.

But this wasn’t a “once-in-a-century” flood. Just two years before, single-day records of water poured down on Chicago for three straight days.

Lower Wacker Drive became a six-foot deep lake. The Chicago River, usually two feet below Lake Michigan, stood more than five feet above the Lake, threatening to contaminate Chicago’s source of drinking water. The sewer system – again, unable to manage such unabating rain – overflowed, bubbling into basements across the city.

How could a “once-in-a-century” flood happen twice in three years? Peter Gleick, of the Pacific Institute, says it well: “If climate change is a shark, the water resources are the teeth.”

This Science News Century of Science post looks back on the last hundred years of humanity’s greatest shark – er, threat: Our Climate Change Crisis.

By the 1850s, scientists were already realizing that the buildup of carbon dioxide in our atmosphere would warm the world. As industrialization took off in the early 1900s, carbon dioxide started pouring into the atmosphere, the byproduct of behemoth amounts of coal burned to power industry.

In 1958, geochemist Charles David Keeling showed that the amount of carbon in the atmosphere was steadily rising. Prior to industrialization, carbon levels had held steady for centuries at 280 parts per million (ppm). In 1958, the “Keeling Curve” – as it came to be known – showed carbon levels ticking at 315 ppm.

While scientists agreed that increased carbon dioxide would warm the world, many believed that warming would take centuries, if not longer. We had time, was the thought. Many politicians and industry leaders were more than happy to double-down on the message and add their own spin to minimize the impacts of a warming world. It took another 30 years before we discovered just how fast the climate can warm.

The Greenland ice sheet is a 2.5-mile thick climate record keeper. It’s made of layers upon layers of compressed snow turned ice, stretching back almost one million years. Within each layer of ice, is a snapshot of the climate at that time. By drilling cores from the ice sheet, scientists can look into the deep past and reconstruct Earth’s climate – and how quickly it can change.

International research teams drilled cores from the Greenland ice sheet in the 1980s and 1990s. The cores let the researchers peer back almost 250,000 years through Earth’s climates. They discovered that not only can rapid warming happen, but that it has happened a lot. In the last 80,000 years, the climate rapidly warmed more than 20 times – and did so in a matter of decades!

“It’s an important reminder of how ‘tippy’ things can be,” says Jessica Tierney, a paleoclimatologist at the University of Arizona in Tucson.

And tippy they are.

For the last 20 years, Chicago was believed to be a “climate haven” – a city shielded from the throes of climate change. What we failed to grasp is that the climate runs on a world-wide scale – everything is impacted, even if we don’t quite know how.

Chicago, seemingly protected from the rising seas and uncontrollable wildfires on the coasts, actually sits in the jaws of the shark. Cradled by Lake Michigan, the rising temperatures caused by climate change have transformed our steady, predictable relationship with water.

Warmer air increases both evaporation and precipitation, creating a warmer and wetter climate spiked by suffocating drought and massive swings in the Lake Michigan water level. And we never quite know where we – or the water – will be.

The “once-in-a-century” floods will continue in the chaotic spurts to which they’ve become accustomed. The shores of Lake Michigan will flood, wreaking a special kind of havoc on South Side neighborhoods. Then the Lake will pull back, seized by a drought inspired by the chorus of Chicago Supercell.

Welcome to the new, warmer, wetter Chicago. Yet, by working together and tackling issues on a hyper-local scale, we can manage the unavoidable, and tell the most unmanageable impacts to come again another day (or millennia).