How big cities are finding innovative ways to nudge people to ditch cars

Governments and public agencies are increasingly partnering with the private sector in the fight against climate change

Home to more than half of the planet's 7 billion people and a large portion of its 1.2bn cars, cities face a huge challenge as the world strives to meet the Paris climate goal of limiting global warming to 1.5C above pre-industrial levels. Cutting emissions in cities is critical: they make up only 2% of the world's total land area, but produce up to 70% of its climate emissions from human activity, according to a 2011 United Nations report.

As they work to reduce emissions, governments and public agencies - which often lack the resources to tackle the weighty global warming problem alone - are increasingly looking to the private sector for help, says Robert Puentes, a senior fellow at the Brookings Institution's Metropolitan Policy Program thinktank.