Throughout the world's oceans, forests of kelp—crucial to biodiversity, carbon sequestration, and coastal protection—are under threat from climate change, pollution, and human development. Will they disappear before we fully understand their massive environmental benefits?

Water expert and MacArthur “genius” award winner Peter Gleick says we can learn much from watching what happens in South Africa. Biggest lesson: The cheapest source of new water is not actually new water.