It sounds like an obscure movement in continental philosophy, but phenology's more down to earth than that.
It's the study of recurring natural events - when the first leaf or the first butterfly appears or when the first swallow departs.
With more than 15,000 amateur recorders around the country, the UK Phenology Network is possibly the largest mass participatory scientific project in the world: and it's coming up with crucial information on climate change.
Mark Whitaker's report focuses on the Network's most cherished collaborators - people who for decades have been quietly and meticulously recording how our seasons are changing.
Mark Whitaker meets the amateur nature watchers around Britain whose meticulous private records are now being collated to provide evidence for climate change.
The UK Phenology network advertised in local newspapers and publications to find anyone who had kept a long-term nature diary.
Among those who replied was Joan Baxter, who started keeping a diary when she was 13 in 1935, and David Grisenthwaite - who has noted every single time he has mowed his lawn for the past 25 years.
Phenology is the study of re-occurring natural events like the first cuckoo or the last swallow.
It dates back to the 18th Century when Robert Marsham began to note 27 indicators of Spring.
Five generations of his family carried on the tradition and the records were kept until the 1950s.