Technically, there is still one more year to complete in this decade; however, it is already the warmest decade since 1880, when “reliable modern” records began. Live Science reports:
According to NASA’s Earth Observatory, 2008 was the coolest year of the decade, and 2009 saw a return to near-record global temperatures (despite that frigid December, which was unseasonably cool for much of North America, Europe, and Asia).
2009 was only a fraction of a degree cooler than 2005, which is the warmest year on record.
James Hansen warns the current El Niño cycle causing big storms in the western US could create unusually high temperatures this summer, like it did in 1998.