Chicago's progress is also part of a national trend. Researchers studied the 30 largest metros and found green certified office space has reached 41% of market totals – an all-time high for the five-year study. According to the report, 11.5% of all buildings surveyed are ENERGY STAR labeled, while 5.2% of buildings are LEED certified, both significant boosts over last year.

Chicago, along with many other top markets, helped push the real estate community to adopt green strategies by instituting a benchmarking ordinance in 2013. It requires large property owners to track and publicize their energy use. And many now see this as a way to market properties to environmentally-conscious tenants and employees.

“From moving to 100% renewable energy in our public buildings, to supporting our private partners as they work to reduce emissions, Chicago is showcasing to the world the impact that cities can have on climate change for their residents and for people around the world,” says Chicago Mayor Rahm Emanuel. “This national recognition is a testament to the progress and success of our efforts to improve our environment while bettering communities across Chicago.”

And with nearly 70% of its space green certified, Chicago stretched out its lead. Sixty-four percent of the market in second-place San Francisco was green certified, and that 6% was the largest ever recorded in the Green Building Adoption Index. Atlanta kept the third spot with more than 58% certified, while a surging Los Angeles claimed fourth – up from sixth last year. Minneapolis was again fifth with 55%.

Pendleton says the attitude of Chicago landlords is “if we're going to do this, let's be bold about it.”