Every picture tells a story - of nature

Make sure you don't discard or delete your holiday snaps this year - they could hold valuable information about how our environment is changing.

In particular, dated images that show plants can provide clues about the timing of events like flowering or leaf budding, which are sensitive to climate change.

Prof Richard Primack and graduate student Abraham Miller-Rushing from Boston University are looking at how plant and animal species has changed in tandem with climate warming in Massachusetts.

They are plundering non-traditional sources like old photos and diaries, sifting through archived plant cuttings and talking to amateur naturalists about common species in the area.

"For many people climate change is a very abstract idea, it seems to be happening far away or it's a discussion that scientists are having," Prof Primack told The Irish Times, "so we are showing that with familiar plants or animals in the eastern United States, people can see changes happening around them."

Changing trends include plants flowering earlier and migratory birds moving their arrival times back by weeks.

The researchers sifted through thousands of dated arboretum plant cuttings and photos. It was a lot of legwork tracking down the photos, says Primack, but it was worth the effort.

They compared the photographic records and old plant specimens with the same species today and found that plants in Massachusetts now tend to flower several days earlier than they did just over a century ago.

This earlier flowering is being driven by warmer spring temperatures, according to Primack, who will publish the study in November's American Journal of Botany.

One photo-comparison shows a striking change in leaf-budding of trees in Lowell cemetery near Boston. An image from May 20th, 1868 - a particularly cold year - shows the chilly graveyard where the trees are bare.

Primack went back to the same spot on the same date in 2005 and found all the trees were fully leafed out. "It's quite dramatic," he says.

Primack's group has also tapped into the personal records of local naturalists. "They were initially sceptical that their diaries could show anything because [ individual] years seemed variable, but when we extracted information about particular species, the patterns are fairly striking."