But the Phenology Network's got a big problem with historical records against which it can judge what's happening now. In the late nineteenth century the Meteorological Office started keeping basic phenological information. But it stopped in 1948. So there's a fifty year 'black hole' until the Network started work in 1998. This programme shows how it's being filled. In April last year a national appeal was launched asking individuals to send in whatever private nature-records they'd been keeping. We talk to a Cambridgeshire woman who began a nature diary when she was a school girl in 1935; to a man in Fife who's kept records for 25 years of when he mows his lawn; to a couple in the Wirral who keep meticulous records of snowdrops and hawthorn blossom; and to a man on the North-East coast who for decades has noted down each day every bird that he sees.

We then talk to the scientists about what all this information adds up to. And its seems that the mass observation of what's happening in back-yards, parks and woods around Britain may be providing clear and troubling evidence of global warming. On average the first leaf appeared 12.6 days earlier in 2003 than in 2001; and migrating woodland birds arrived three days earlier. Millions of people have been fascinated by BBC television's Springwatch initiative. With this programme we go deeper into the little-known world of phenology to report findings that can only be deeply troubling to us all.