Critics have long derided the world's biggest cities as disorderly, overcrowded and polluted. But in recent years, as the planet's population continues to rise past seven billion and more and more people flock to urban areas, some now argue that cities may hold the key to sustainable growth.
Millions of young girls around the world, some as young as five, are forced into marriage every year. The practice is forbidden by international agreements and outlawed in many countries. But many young brides end up in abusive relationships without access to courts or education.
Clean, fresh water is an essential element to life — not only do people and animals depend on it, but it also sustains many businesses and agriculture. The majority of the fresh water used worldwide goes to irrigation, and the need is expected to rise with the growing global population.
Three months after the tsunami and nuclear disaster struck Japan, AP photographer David Guttenfelder ventured into the exclusion zone around the Fukushima Daiichi nuclear power plant. The only non-Japanese photographer allowed in, he captured crumbling reactor buildings and haunting footprints.