As carbon dioxide builds up in the atmosphere, the Earth will get warmer. Exactly how much warming will result from a certain increase in CO ₂ however, is being investigated. The relationship between CO ₂ and warming, known as climate sensitivity, determines what future we should expect as CO levels ₂ they keep rising. New research led by the University of Washington analyzes the last ice age, when much of North America was covered by ice, to better understand the relationship between CO ₂ and global temperature. It found that while most future warming estimates remain unchanged, the absolute worst-case scenario is unlikely. (University of Washington, more at phys.org)