Global warming, a spark for spring's early arrival up north, appears to be delaying its appearance in southern states, the New Scientist reports. Southern leaves are coming later, not earlier, according to a Maryland researcher. "It's really surprising," says Xiaoyang Zhang of Earth Resources Technology. "Nobody had noticed how warming temperatures can delay the green-up."
Why the delay? Some plants may be unable to sprout without a cold snap, Zhang says—which is less common now in hotter climes. Below 31 degrees north, plants are blossoming 0.15 days later on average; above 40 degrees, 0.32 days earlier. The season reversal will likely upset farmers and lilac-peepers alike below the tipping-point 35th parallel.