Scientists claim to have produced the first conclusive proof that spring is arriving earlier as a result of global warming.
In Britain trees are coming into leaf 10 days earlier than they did 30 years ago while in countries with more pronounced warming, such as Spain, they are doing so by a fortnight. On average spring has advanced by between six and eight days across Europe.
According to the study, the biggest of its kind, the extended growing season has resulted in autumn being delayed by three days.
Tim Sparks, of the Centre for Ecology and Hydrology in Huntingdon, Cambridgeshire, one of the report's authors, said the findings were based on the most extensive data available.
He said in the past climate change sceptics were able to cast doubt on studies that suggested the timing of the seasons was changing with accusations that scientists were "cherry-picking" data that supported the global warming theory. But after using 125,000 sets of observations of 542 plant and 19 animal species in 21 countries, he said the evidence was now incontrovertible.
"Not only do we clearly demonstrate change in the timing of the seasons, but that change is much stronger in countries that have experienced more warming," he said.
Spain, which is growing hotter more quickly than any other European country, has experienced the most pronounced change, the report found.
Countries to the east and north are warming relatively slowly and had changed the least. In Slovakia, spring was arriving only three days earlier.
Dr Sparks said that the study was particularly effective because it used species that grow across all countries in Europe. Scientists examined the date that beech trees (fagus sylvatica) and wild cherries (prunus avium) came into leaf to measure the changes, giving a consistent picture of the effect of warming, the authors said.
Annette Menzel, of the Technical University Munich, who co-wrote the study, said the findings had profound implications. "Unlike some studies that record individual species, this is the first comprehensive examination of all available data at the continental scale, and the timing of change is clear, very clear," she said.
Temperatures have increased by 0.6C in the past 100 years, with the 1990s the hottest decade on record. Some models predict that by the end of the century, the Earth could be 5C warmer.
As well as changes in the timing of natural events, such as the leafing of trees, the arrival of migrating birds and the spawning of frogs, scientists point to other indicators of warming in Europe.
Spain and other southern European countries have been hit by severe drought and forest fires, while in the centre of the Continent, Alpine glaciers have been retreating. In Britain, the warmest days of the year are getting hotter while there are fewer very cold days in winter.
Dr Sparks said the level of global warming to date was "only modest", and that greater challenges lay on the horizon.
"The rate of change is extraordinary. The real concern is what's going to happen in the coming century, when temperatures are going to continue to rise. We can't stop it but we can slow it down."
Biologists in the UK, with the assistance of a mounting body of data supplied by the public, have been building up evidence over 30 years to suggest that spring is coming earlier.
Spotting the changing seasons has become a ritual for millions of amateur phenologists, not least through mass-participation events such as the BBC's Springwatch series, presented by Bill Oddie.
One of the key developments came in 1998 with the creation of the UK Phenology Network, run by the Woodland Trust and the Centre for Ecology and Hydrology. It has found that birds are arriving 3.7 days earlier than they did in the benchmark year 2001, while nesting is now taking place on average eight days earlier. There are also growing numbers of reports of over-wintering house martins and swallows, birds that normally migrate south to Africa for the winter.
The insect world has been found to be particularly sensitive to temperature changes, with some species being spotted progressively two weeks earlier.
Frogspawn and toadspawn is one of the most easily identifiable signs of spring. The earliest recorded sighting was in Pembrokeshire in November 2004, while phenologists regularly see it at the Lizard in Cornwall in December.
It is estimated that the breeding cycle of amphibians is now on average eight days earlier than it was five years ago.
Temperatures in March and April remain critical for the timing of spring. In 2004 - the fourth hottest year on record - January and February were warmer than the same months in the previous year. However, because March and April were cooler, the key natural events that indicate the arrival of spring were later. Meanwhile, phenologists are now keen to build up a picture of autumnal changes, for which there is only 10 per cent of the data that exists for spring.
* Butterflies: For every 1C temperature rise, the ringlet (aphantopus hyperantus) has been seen a week earlier. The comma (polygonia c-album) and holly blue (celastrina argiolus) have been spotted in March
* Birds: The chiffchaff (phylloscopus collybita) and blackcap (sylvia atricapilla) are arriving in Britain earlier. Migratory birds now arrive 3.7 days earlier than in 2001.
* Red-tailed bumblebee: The bombus lapidarius can be found in gardens and grasslands from the first warm days of spring - from March in the South, later in the North.
* Amphibians: Frog and toadspawn was reported in Pembrokeshire in November 2004 and seen in Cornwall in December.
* Snowdrops (galanthus) and lesser celandines (ranunculus ficaria): Have been spotted flowering before Christmas in the South-west.
* Seven-spot ladybird: Coccinella 7-punctata can be found in gardens, woodlands and hedgerows from February.Reuse content