How hot is it going to get? This is one of the most important and difficult remaining questions about our changing climate. The answer depends not only on how sensitive our climate is to greenhouse gases, but also on how much carbon dioxide (CO2) and other greenhouse gases we as a civilization choose to emit over coming decades. In order to help think more clearly about this question, we asked authors who have contributed to the reports of the Intergovernmental Panel on Climate Change (IPCC) to share their best guesses about where the world is headed. The results of our…