Early-blooming flowers and trees at the Royal Botanic Gardens strongly support the view of scientists who claimed last week that spring is arriving in Europe on average six days earlier than it was 30 years ago.
Like the blossoms of the purple-leaved plum, Prunus cerasifera atropurpurea, scores of plants at Kew are currently flowering up to a month early, according to Nigel Hepper, who has carefully noted flowering dates in the west London gardens for 40 years.
When he began, the plum was a species that regularly flowered in the last week of March, and his meticulous records show it appearing as late as 13 April in 1979. But this year, it came out in the last week of January and it is now nearly finished.
"It normally comes out in the last week of March," said Mr Hepper, holding a branch close to his face.
"This year it came out in the last week of January. Two months earlier than in the past. Remarkable. Remarkable."
Kew's wild daffodils, Narcissus pseudonarcissus, came out as late as 10 April in 1958 but have been flowering for much of February and are now also nearly over.
Across the gardens, the story is the same: the pink of Prunus subhirtella, the weeping spring cherry, the intense lilac of Lathraea clandestina, American toothwort, the glorious bright blue of Scilla bifolia, Alpine squill, are all, by Mr Hepper's calculations, visible very much earlier than they were two or three decades ago.
Scientists from the University of Munich claimed last week in the journal Nature that Europe's new early spring is due to global warming, caused by the build-up of carbon dioxide and other industrial gases in the atmosphere.
Mr Hepper's recording of Kew's flowering dates has been entirely unofficial and a pasttime, because such monitoring was previously regarded as somewhat "trainspotterish" by other scientists. "It doesn't cost anything and needs no sophisticated equipment, so it was rather frowned upon."
But the advent of the threat of climate change and its potential disruption of all ecosystems has suddenly made its value as an important indicator clear. Imperial College, London, is now collating his records into a proper database.
As a botanist rather than a climatologist, Mr Hepper, 69, a rainforest expert who has now retired, cannot be sure of the cause, but he is certainly sure of the effect.
His records of 5,000 different species show, without doubt, that many of Kew's flowers, shrubs and trees are pushing up, budding and flowering much sooner than they once were. Is it global warming? "Let's say it looks very suspicious."
And by how much has spring shifted? "My impression is that over 40 years, it is several weeks earlier."
He smiles. His 70th birthday is in a fortnight. "The trouble is, one doesn't live long enough to confirm it, or otherwise."
Looks fairly convincing from here, Mr Hepper.
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