Scientist Dr. Paul Mayewski.

An expert in climate change research, Paul Mayewski led the National Science Foundation's Greenland Ice Sheet Project 2. The project extracted ice cores chronicling 100,000 years of climate history. Mayewski, with co-author Frank White, writes about their expeditions in the new book, The Ice Chronicles: The Quest to Understand Global Climate Change (University Press of New England). Mayewski is also co-director of the Institute of Quaternary and Climate Studies at the University of Maine.

Journalist Chloe Sorvino says the meat industry pollutes the environment, contributes to climate change and leaves the meat supply chain vulnerable to major disruptions.

New York Times science writer David Wallace-Wells says the cost of solar and wind energy has fallen dramatically. Nevertheless, we're still facing painful, long-lasting changes to the planet.