By 2050, the world's major cities will be crowded by six and a half billion people. Pollution, inequality, and climate change threaten the living standards that cities can offer. Yet people designed these problems and people can design their solutions. CNN profiles the cutting-edge projects that combat the pressures modern cities face. Innovators in the UK and Ghana are turning to natural, yet surprising, resources to reduce their carbon footprint, while scientists in the Netherlands and India are finding ways to protect their citizens from the ravages of climate change, whether it is rising sea levels or extreme temperatures. And in Australia, a new approach to urban planning melds nature with modern cool in the world’s largest vertical garden