The Fourth National Climate Assessment, released Friday by the U.S. government, puts it starkly: “Observations collected around the world provide significant, clear, and compelling evidence that global average temperature is much higher, and is rising more rapidly, than anything modern civilization has experienced, with widespread and growing impacts.” The report notes that “annual average temperatures have increased by 1.8°F across the contiguous United States since the beginning of the 20th century” and that “annual median sea level along the U.S. coast . . . has increased by about 9 inches since the early 20th century as oceans have warmed and land ice has melted.”
