Last year, global warming reached record high temperatures — and if that news feels like déjà vu, you're not going crazy. The planet has now had three consecutive years of record-breaking heat.

Guest: Robert T. Harris.

Today on Focus, we'll discuss the theory of global warming with Robert T. Harris, Chief Scientist and Director for Environmentally and Socially Sustainable Development at the World Bank.

Guest: Stephen Schneider.

According to the National Academy of Sciences, the surface temperature of the Earth has risen by about a degree in the last 100 years. Many scientists argue that most of the warming over the last 50 years is due to human activity. Others say we don't have enough data to draw that conclusion. This morning on Focus, we're joined by Stanford biologist Stephen Schneider to explore the question of whether climate change is too uncertain for policy.