That's because certain plants and animals are dependent on each other for food and shelter. If the plants bloom or bear fruit before animals return or surface from hibernation, the critters could starve. Also, plants that bud too early can still be whacked by a late freeze.

The young of tree swallows — which in upstate New York are laying eggs nine days earlier than in the 1960s — often starve in those last gasp cold snaps because insects stop flying in the cold, ornithologists said. University of Maryland biology professor David Inouye noticed an unusually early February robin in his neighborhood this year and noted, "Sometimes the early bird is the one that's killed by the winter storm."

The checkerspot butterfly disappeared from Stanford's Jasper Ridge preserve because shifts in rainfall patterns changed the timing of plants on which it develops. When the plant dries out too early, the caterpillars die, said Notre Dame biology professor Jessica Hellmann.

"It's an early warning sign in that it's an additional onslaught that a lot of our threatened species can't handle," Hellmann said.

It's not easy on some people either. A controlled federal field study shows that warmer temperatures and increased carbon dioxide cause earlier, longer and stronger allergy seasons.

"For wind-pollinated plants, it's probably the strongest signal we have yet of climate change," said University of Massachusetts professor of aerobiology Christine Rogers. "It's a huge health impact. Seventeen percent of the American population is allergic to pollen."

While some plants and animals use the amount of sunlight to figure out when it is spring, others base it on heat building in their tissues, much like a roasting turkey with a pop-up thermometer. Around the world, those internal thermometers are going to "pop" earlier than they once did.

This past winter's weather could send a mixed message. Globally, it was the coolest December through February since 2001 and a year of heavy snowfall. Despite that, it was still warmer than average for the 20th century.

Phenology data go back to the 14th century for harvest of wine grapes in France. There is a change in the timing of fall, but the change is biggest in spring. In the 1980s there was a sudden, big leap forward in spring blooming, scientists noticed. And spring keeps coming earlier at an accelerating rate.

Unlike sea ice in the Arctic, the way climate change is tinkering with the natural timing of day-to-day life is concrete and local. People can experience it with all five senses: