The actual conclusions of this report don't diverge a whole lot from the previous assessments. It "represented more of a refinement," according to Graeme Stephens, Director of the Center for Climate Sciences at NASA's Jet Propulsion Laboratory. Stephens was a lead author, a contributing author and an expert reviewer on three different chapters within the assessment. "The conclusions fundamentally are, the planet is warming," he tells Popular Science. Many of the changes between this assessment and the last one, published in 2007, have to do with refining the models used to predict climate change outcomes.