The world’s cities are coming up with ingenious ways to fight climate change, from massive sea walls to "sponge zones" and floating communities.

Urban areas have reason to act. Many are already grappling with impacts such as rising sea levels and extreme weather. They’re experiencing more frequent floods, power outages, and deadly heat waves.

"The trend of climate change is a major dynamic that cities will be reckoning with over the next several decades," says Bryna Lipper, vice president for relationships at 100 Resilient Cities, a nonprofit.

Lipper's group is helping cities hire "chief resilience officers" to look at the big picture. "No longer will it work to have a system of silos," she says.

With that comes a different way of thinking about both mitigating and adapting to climate change, from the roads to the treetops.

The story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.