The white-coated scientist explained calmly to the trigger-happy superheroes that the deadly menace they had come to Earth to fight was already under control.

“In the 80s, the global community came together to address the destruction of the ozone layer,” Dr. Sharma said. “The 80s? Did they all have cool hairdos?” quips the Star Lord.

The science and politics of the atmosphere can be rather sober subjects. But a dash of humour and imagination is helping spread the good news that determined global action really can save the planet.

How do we prepare for the doubling of the global urban population by 2050? By dramatically rethinking urbanism and its governance. That means designing cities for people, not cars; allowing everyone access to urban opportunities; investing in resource-efficient buildings, transport, energy, water and waste systems; and enabling cities to experiment and to learn from each other.