Clinton: Climate change is the world's biggest worry "First, I worry about climate change," Clinton said in an onstage conversation with the founder of the World Economic Forum. "It's the only thing that I believe has the power to fundamentally end the march of civilization as we know it, and make a lot of the other efforts that we're making irrelevant and impossible." Clinton called for "a serious global effort to develop a clean energy future" to avoid the onset of another ice age. I'm confused. Do we worry about global warming, or another "ice age?"