eBusiness Weekly
Chicago is sinking. From melting glaciers to underground hotspots, global warming could threaten the city’s elegant skyscrapers and breathtaking lakefront, climate scientists say.
Of course, this Midwestern metropolis is far from alone in suffering the scourge of subsidence. Venice, Jakarta, New York and cities along the US East Coast are all sinking too. But marooned inland, Chicago doesn’t share their rising sea-level worries — although it was built on marshland.
According to a recent study by Northwestern University, there’s a “silent hazard” beneath the streets: subsurface heat islands that deform the ground.
Northwestern researcher Alessandro Rotta Loria says it’s the first study to quantify the effect of “underground climate change” on urban infrastructure, which threatens cities around the world, especially those built near water.
He and his team collected three years of temperature data from 150 underground sensors and found that beneath some buildings in the Chicago Loop — those in the central business district that create the famous skyline — it can be 18F hotter than under local Grant Park, a large green area near Lake Michigan.
He says underground climate change is the subterranean corollary of the “surface heat islands” in many US cities, but more subtle.
Garages, basements, tunnels and underground transportation systems emit heat into the ground and in a dense area such as the Loop, this causes it to expand or contract.
Rotta Loria says subsurface heat islands “don’t kill people” and they aren’t likely to cause buildings to collapse, but adds that “in the long term, underground climate change can be very costly” because it can cause or exacerbate shifts, tilts and cracks in buildings and infrastructure, and significantly raise repair and maintenance costs.
But subterranean climate change isn’t the only danger.
According to the National Oceanographic and Atmospheric Administration, Chicago has sunk at least four inches in the past 100 years due to much earlier climate change: the melting of the glaciers that covered the area thousands of years ago.
Land continues to rise and fall after losing its ice-age burden. Jacob Heck, Great Lakes regional geodetic adviser for NOAA’s National Geodetic Survey, says the land in the Great Lakes basin has tilted up or down by a combined two feet over the past century.
So the bad news is: Chicago is sinking. But the good news might be that postglacial sinking has been going on for so long.
Heck says he’s not too worried about the threat to Chicago’s architectural masterpieces: “By the time those structures went up we were aware of those effects so I wouldn’t be as worried about Chicago skyscrapers as I’d be about old buildings in Venice.”
And Seth Stein, emeritus professor in the department of Earth and planetary sciences at Northwestern, says he’s more worried about the wild fluctuations that have been normal in Lake Michigan water levels for decades.
“The single biggest effect on the city of Chicago is lake flow,” he tells me.
As a Chicagoan, I agree: four years ago, I was writing about record high lake levels and disappearing beaches. This year, the lake has receded so much that there are beaches I’ve never seen before.
This year’s historically mild Midwest winter means Great Lakes ice cover has hit its lowest point since records began in 1973.
Stein points out that Chicago’s skyscrapers are mostly protected from Lake Michigan by the “buffer zone” of its large lakeside parks.
He predicts “we will be dealing with very large climate effects in future”, but most likely they will be “things we haven’t even really thought about yet. Because things are engineered for the way they are now — not the way they will be”.
Still, the city has reinvented itself before. In the mid-19th century, city planners jacked up the level of Chicago — built on marshland just above the water table — by as much as 14 feet, so they could install underground sewers.
And in 1900 they reversed the flow of the Chicago River so it would no longer dump waste in Lake Michigan. Chicago has long literally defied gravity: it may be sinking; but it’s not sunk yet. — Wires
