While some climate-related threats can seem abstract, water scarcity is visceral and immediate, palpable in the crunch of drought-ravaged crops or the sting of a parched throat. Guli, an Australian corporate-lawyer-turned-activist, started Thirst to educate consumers about water conservation, but this year the 45-year-old upped the ante, running 40 marathons across seven deserts on seven continents—in just seven weeks—while collecting conservation pledges online. On March 22, World Water Day, she completed the 1,048-mile journey of the 7 Deserts Run. “Never seen a better example yet of #gobigorgohome,” tweeted a fan in Hong Kong.

This article is part of the 2016 World’s 50 Greatest Leaders list, our annual directory of world-changing leaders in business, government, philanthropy and beyond. Click here to see the entire package.