'Final' climate report

Unsettling unknowns

- JUSTIN WORLAND

THE SCARIEST PART OF A LANDMARK NEW climate report may be what scientists don't know. On March 20, the U.N. International Panel on Climate Change (IPCC) released the final volume in a series of reports outlining experts' latest understanding of climate science. It declared the science "unequivocal" and warned that even with urgent action we will face a dramatic uptick in catastrophic events from droughts to floods that have become telltale signs of a rapidly warming world. But for all that scientists can confidently say, most worrisome are the "known unknowns"-potential outcomes scientists know could happen even if they don't know exactly when or how. Near the middle of the 37-page summary for policymakers, scientists explain the "likelihood and risks of unavoidable, irreversible or abrupt changes."