The National Science Foundation asks: How do we know the climate is changing? Is it just part of a natural cycle, or are humans driving the change? Richard Alley, glaciologist and professor of geosciences at Pennsylvania State University, leads a discussion with some of the world’s leading climate scientists. Join Alley and his panel as they explore these questions, laying out the line of reasoning that has led the Intergovernmental Panel on Climate Change and many other scientific groups to conclude that humans are very likely the cause of the majority of current warming. This lively exploration into the fundamentals of climate change gives us a glimpse into the treasure trove of the deep past to see what might lie ahead in a warmer world. From the Series:To What Degree? What Science is Telling Us About Climate Change