Hidden advantages

not even in his wildest dreams would an amateur phenologist assume that his records would aid modern, scientific climate change studies. But this is happening. Records of amateur phenologists are proving to be invaluable to researchers studying climate changes (www.nature.com, January 2, 2002). Worldwide, researchers are combining the amateur records with climate data, to reveal how, for example, changes in temperature affect the arrival of spring. One such researcher is Terry Root, an ecologist at the University of Michigan in Ann Arbor, usa. She has collected bird watchers' counts of wildfowl taken between 1955 and 1996 on seasonal ponds in the American Midwest and combined them with climate data and models of future warming. Her analysis shows that the increased droughts that the models predict could halve the breeding populations at the ponds. "The number of waterfowl in North America will most probably drop significantly with global warming," she says.

Overall, such endeavours have helped to show that a number of natural events -- from the opening of leaves to the return of birds from migration -- now occur much earlier across much of the northern hemisphere than they did 20 years ago. The amateur data also gives indication about how nature will change in the future. For example, hawthorn trees are predicted to flower about 10 days earlier for every degree of warming.

But not all professionals are happy to use amateur data. Ecologist Marcel Visser of the Heteren-based Netherlands Institute of Ecology says that only when several independent records say the same thing can you believe them. Different observers can have different ideas of what constitutes, for example, an open snowdrop. "The biggest concern with ad hoc observations is how carefully and systematically they were taken," says Mark Schwartz of the University of Wisconsin, Milwaukee , usa, who studies the interactions between plants and climate. "We need to know pretty precisely what a person's been observing -- if they just say "I noted when the leaves came out", it might not be that useful."

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