Richard B. Alley, glaciologist The Pennsylvania State University
Our greatest challenge is maintaining and improving our humanity without degrading Earth and its ability to support us. We face many hurdles. One especially high hurdle is learning how the Earth system works, and how we interact with it. Climate and ecosystems change naturally, and in response to things we do. Those changes may be good or bad for us and for other living things. We must recognize and deal with those changes: humans have been changing the Earth and its living things since we mastered fire and spear, no place on Earth is free of our influence, and the changes we caused cannot disappear quickly. Our best hope is to educate ourselves and each other on how the Earth works, and to use that knowledge to co-exist with the Earth.