What does climate change look like? For many people, the first — or perhaps only — image that comes to mind is of smokestacks, or polar bears perched on ice floes.

"If you go to Google and click on climate change images, you have to go a long way before you hit many images of people," says Adam Corner, research director at Climate Outreach, an Oxford-based think tank that aims to boost public engagement on climate change.

But climate change already is affecting billions of people around the world, from farmers in Zimbabwe experimenting with new crops to battle drought to grandmothers in India who earn cash selling solar home lighting systems, or children in the United States coping with a longer allergy season.