The notion that extra, human-generated CO2 might drive temperatures too far the other way was convincing. But if warming was on the way, it was too gradual to be detected. That's no longer true. While the globe has warmed just 1 degree Fahrenheit on average over the past 100 years, a little temperature rise goes a long way, and the trend is accelerating. The three hottest years in the past century have come in the past decade, and 1995 was the sultriest on record.
Spring arrives a week earlier in the northern hemisphere than it did a decade ago.
Mountain glaciers are melting all over the world, and the permanent sea ice surrounding Antarctica has receded dramatically. Unusually severe weather has been more frequent in the past few years, quite plausibly a consequence of both higher temperatures and the increased evaporation and precipitation they'd be likely to cause. Flora and fauna are showing the impact of a hotter planet too. Animals that thrive in warmer climates, like the Edith's checkerspot butterfly in the American West, have begun to extend their range northward, while cold-loving creatures such as brook trout have vanished in some areas. Plants are pushing to higher latitudes and higher altitudes.