From 1 January, an extensive variety of Kew's plants, from wild daffodils to horse chestnuts, are to be carefully monitored annually to see if they are responding to a warmer world by flowering sooner.
Earlier this year, scientists from the University of Munich - in a paper published in Nature - claimed that spring was arriving in Europe on average six days sooner than it was 30 years ago, and suggested global warming was the cause.
Last week, climate researchers at the University of East Anglia also revealed that 1999 was the warmest year for England since the national temperature record began in 1659, and the fourth hottest year for the world as a whole. Eight of the 10 hottest years globally have occurred since 1990.
Kew's scheme, an initiative of the new director, Peter Crane, will in effect use the world's most celebrated botanical garden as a giant and ultra-sensitive laboratory to detect climate change, and test the earlier- spring hypothesis by building up over the years a massive database of precise flowering dates.
Kew, in south-west London, is an ideal site, as it hosts 32,000 species of plants from around the world, looked after by a scientific staff of several hundred. Yet the emphasis on monitoring their flowering dates is quite new.
As flowering times are subject to natural variations as big as the weather itself - Kew's snowdrops may appear in either January or February, depending on warm or cold winters - it has never before seemed necessary to record them every year.
But in the context of global warming it is now clear that, despite the natural variations, a long run of data can show a definite trend indicating climate change and, in the jargon, "pick out the signal from the noise". Kew's scheme has a head-start because, although flowering times have not been officially monitored, there are unofficial records going back nearly half a century, which have been collected by one man, Nigel Hepper, a former assistant keeper of the Herbarium, Kew's museum of dried plant material.
Since starting work at Kew in the early Fifties, Mr Hepper, now 70, has collected flowering dates for nearly 5,000 species, although not all are continuous. His information will be taken over officially by the Royal Botanic Gardens and incorporated into its database, and a list he has suggested of 100 plants to be monitored in future will provide the basis for Kew's project.
They range from exotic trees and shrubs such as the mock orange and the Judas tree to native flora such as ox-eye daisies, kingcups, and Kew's famous bluebells.
"Nigel's own database is pretty fantastic," said Professor Crane, an Englishman who was previously director of the Chicago Field Museum and took over at Kew from Sir Ghillean Prance last August. "He has several decades' worth of data and we will systematise that, as well as monitoring species every year from now on, for when they first come into full flower.
"There does seem to be an impression that things are flowering earlier, but we want to be clear what the trend really is. If there is significant climate change as we move into the new century, the implications are huge."
Mr Hepper's own records do indicate a change, and last February, for example, he could point to a whole series of flowers and trees bursting into bloom at Kew a month and more sooner than expected, including a plum that in 1979 flowered in mid-April, but this year came out in January. "It's definitely my impression that things are flowering earlier," he said. "I'm delighted that Kew is now taking the project on officially."Reuse content