Climate change, with its rising temperatures and rising sea levels, its wildfires and extreme weather events, is a profound threat to much of the life on this planet, including human life. And yet we are not taking anything close to the steps necessary to mitigate this existential challenge. Bob explores some of the hard truths about climate change with his guest - one of the wisest minds on this issue - Alex Halliday, director of the Earth Institute at Columbia University.