The New York Times got its hands on a draft of the next Intergovernmental Panel on Climate Change report, which is due to be completed next month. One conclusion: if we proceed as we are proceeding; that is, if there is no big change in human activities to mitigate climate change, sea levels could rise by 3 feet by the end of the century. On sea level, one of the biggest single worries about climate change, the new report goes well beyond the one from 2007, which largely sidestepped the question of how much the ocean could rise this century. The new report lays out several scenarios. In the most optimistic, the world’s governments would prove far more successful at getting emissions under control than they have been in the recent past, helping to limit the total warming. In that circumstance, sea level could be expected to rise as little as 10 inches by the end of the century, the report found. That is a bit more than the eight-inch rise in the 20th century, which proved manageable even though it caused severe erosion along the world’s shorelines. At the other extreme, the report considers a scenario in which emissions, which have soared in recent years, continue at a runaway pace. Under those conditions, sea level could be expected to rise at least 21 inches by 2100 and might rise a bit more than three feet, the draft report said. Hundreds of millions of people live near sea level, and either figure would represent a challenge for humanity, scientists say. But a three-foot rise in particular would endanger many of the world’s great cities — among them London, Shanghai, Venice, Sydney, Miami, New Orleans and New York. If you are in elementary school today, you may live to see the day that some of the world’s greatest cities may become uninhabitable.