While some climatologists study tree rings to decode the history of climatic change, others are scrutinizing a different kind of tree record: century-old forest photographs.

By comparing contemporary photos with shots from a century ago, "you can literally see that trees are leafing out and the plants are flowering earlier now," says [Richard] Primack, of Boston University. [DISCOVER Magazine]

In a study published in the American Journal of Botany, Primack and his colleague, Abraham Miller-Rushing, discovered something interesting after analyzing 286 century-old photographs of Concord, Massachusetts, and Boston's Arnold Arboretum: The leaves are coming out 10 days earlier on average than they did a century ago.

"These kinds of changes are already being seen in Boston, and they will be seen in the rest of the United States in the next 100 years," he says. "We're going to see enormous changes in the distribution of plants and animals, agricultural patterns, and patterns of rainfall." Some plants may even begin flowering before pollinators are around to fertilize them. Hay fever could blossom, too, cautions Primack: "Plants may have a longer season of pollen production, which may extend the allergy season." [DISCOVER Magazine]