One way to tell that the world (or at least this country) is warming is to take a look at the map the USDA puts on the back of seed packets, which shows that winter temperatures have risen pretty much everywhere in the U.S. The Department of Agriculture released an update to the 1990 version of its "Plant Hardiness Zone Map," which classifies the U.S. into 26 different temperature zones based "average annual minimum winter temperature" so plant growers can decide what sort of seeds will germinate and thrive where they live. The 1990 version is based on data collected from 1974 to 1986, while the new one's based off of a broad timespan of 1976 to 2005. The new map reveals much milder winters than in the past.
The USDA "repeatedly tried to distance the new zones on the map from global warming," according to the AP, but with headlines like "Global warming felt in gardens" you can guess what angle news organizations went with. We find ourselves agreeing with Boston University biology professor Richard Primack, who says that "people who grow plants are well aware of the fact that temperatures have gotten more mild throughout the year." But compare for yourself with the 1990 and 2012 versions from The Washington Post, below: