Scientists writing in Environmental Research Letters estimate that the onset of spring plant growth will shift by a median of three weeks over the next century - and global warming is to blame.

The scholars from University of Wisconsin-Madison applied the extended Spring Indices to predict the dates of leaf and flower emergence based on day length. These general models capture the phenology of many plant species.  Their results show particularly rapid shifts in plant phenology in the Pacific Northwest and Mountainous regions of the western US, with smaller shifts in southern areas, where spring already arrives early. Much of their data is available at

"Our projections show that winter will be shorter - which sound greats great for those of us in Wisconsin" explains ecologist Andrew Allstadt. "But long distance migratory birds, for example, time their migration based on day length in their winter range. They may arrive in their breeding ground to find that the plant resources that they require are already gone."

The researchers also investigated so-called 'false springs' - when freezing temperatures return after spring plant growth has begun. They showed that these events will decrease in most locations. However a large area of the western Great Plains is projected to see an increase in false springs.

"This is important as false springs can damage plant production cycles in natural and agricultural systems" continues Allstadt. "In some cases, an entire crop can be lost.

"We are expanding our research to cover all kinds of extreme weather, including droughts and heat waves. We are particularly interested in how these affect bird populations in wildlife refuges."