In the not-so-distant past, cities competing to host the Olympics focused on size, infrastructure and the ability to build huge sporting arenas. Sustainability really wasn’t part of the equation.

But as illustrated with the current bidding war for the 2016 Summer Olympics, times have changed.

The four leading cities – Chicago, Madrid, Tokyo, and Rio de Janeiro – are all trying to outsell each other as being capable of providing the greenest Olympics yet.

Chicago is promising a low-carbon “Blue-Green” event focusing on low-carbon vehicles, renewable energy, reusable storm water, recyclable and reusable products and adherence to green building standards.

Meanwhile, Tokyo is offering  a zero-waste event where fuel cell and electric vehicles are the norm and everything is  powered with green energy sources, with much of the energy obtained from solar panels from the main stadium’s roof.

Madrid, on the other hand, pledges that not only would its Olympic Village would be a showcase of sustainable building, but the city would also establish thousands of hectares of new parkland, complete with bicycle lands and hundreds of thousands of trees.

And in Rio de Janeiro, where slums and luxurious resorts stand side by side, the focus is on four basic tenets of sustainability: water conservation, renewable energy, waste management and social responsibility. Already, Lagoa Rodrigo de Freitas, the proposed venue for rowing and flat-water canoe/kayak competitions of the 2016 Olympic and Paralympic Games, has had a thorough clean up. And that, Rio de Janeiro says, is only the beginning.

First Lady Michelle Obama is working to persuade the International Olympics Committee (IOC) to send the torch Stateside to Chicago in 2016. They will meet in Copenhagen October 2nd.

Which city do you predict will host the games?

Shown: Chicago 2016 proposal