In 2012, the world experienced dozens of extreme weather events, including droughts, heat waves, cold spells, extreme rainfalls, big storms like Superstorm Sandy, and a record-low Arctic sea-ice extent. Teasing apart the factors that create extreme weather is a challenge for scientists, especially when it comes to determining whether human-induced climate change plays a role. Recently, 18 different research teams — comprising 80 scientists — took on that challenge.