The largest of these mega-cities already exceeds 60 million people and the trend is set to continue.
Kolkata faces some of the world's greatest climate challenges, urban heat among them. Here's what some scientists think will help.
School streets and play streets are also an important implication the new civic activities.
This could be bad for mammals in the short term because mosquitoes are potentially biting us later in the season.
Cities including Berlin, Madrid and Toronto ranked highly for climate actions that protect real estate assets and investment.
As Europe considers France's controversial ban on short flights, a new study from Germany details the potential positives and pitfalls.