Early arrival of butterflies demonstrates impact of climate change

Britain's astounding April, the warmest on record, has produced an astounding effect in the natural world, with at least 11 species of butterfly making their earliest recorded appearances this spring in what will be seen as the most remarkable demonstration yet of the effects of climate change on Britain's wildlife.

For several years biologists have been watching warming temperatures affect living organisms, with leaves opening, birds nesting and insects emerging earlier. But what has happened in 2007 with butterflies has been quite exceptional.

Of our 59 resident and regular migrant species, 37 have now appeared, and of these, all except one (the orange tip) have emerged earlier than they would have done a decade ago, according to the wildlife charity Butterfly Conservation.

More remarkably still, 11 of them have broken all records for early emergence, some by scarcely-believable margins.

The Lulworth skipper, which normally appears in the third week of June, was recorded in its Dorset downland habitat near Weymouth on 28 April, seven weeks early, while the speckled wood, normally out and about at the end of March, was seen in Cornwall on 16 January, also seven weeks ahead of its record. The green hairstreak, the chalkhill blue and the wall brown were all recorded six weeks earlier than ever before.

Other record-breakers were the large skipper (a month earlier than ever), the small blue (also a month), the meadow brown (a month), the Adonis blue (three weeks), the brown argus (a fortnight) and the holly blue (also a fortnight). On average, these butterflies all emerged more than four-and-a-half weeks before they would have done during the mid-1990s, according to Butterfly Conservation's records.

"We have been monitoring Britain's butterfly populations for decades, but we have never seen anything like this," said Martin Warren, the charity's chief executive. "It's quite extraordinary. I myself saw the Lulworth skipper on 28 April. My wife called my attention to it and I photographed it, but I could scarcely believe it."

Butterfly Conservation's experts are confident that only global warming can explain the changes. "Butterfly data, collected by hundreds of UK recorders, definitely points to climate change," Mr Warren said. "Species are not only emerging early, but several species are extending their geographic range northwards. The small skipper, the comma and the holly blue butterflies have all crossed the border into Scotland in the past few years, very probably as a result of the changing climate."

There is a possible 12th species that may have broken its record: the large white, usually appearing in early April, but seen on 19 January. However, it is possible that this insect may have been bred in captivity.

Many people saw butterflies on the very warm days experienced in January, especially the red admiral, the peacock, the small tortoiseshell and the comma. But although this is not usual, they are all related species who share the survival strategy of overwintering as adults - compared with some species which overwinter as eggs or chrysalises - so a very warm day in January can simply wake them up.

With the 11 species which have broken early-emergence records, their whole life cycle has been speeded up dramatically.

April 2007 was the culminating month of the hottest 12 months, taken together, ever recorded in Britain, with a provisional mean temperature of 10.4C. April itself was the hottest April since records began in 1659, and it followed the second-warmest winter since records began in the UK, and the warmest-ever autumn.

Spring, at least in southern Britain, has in effect been a full month early this year, and many wild flowers, such as foxgloves, are also appearing far in advance of normal. The early season has created severe problems for exhibitors at the Chelsea Flower Show, which opened yesterday, as flowers have been coming into bloom far ahead of the show dates, and have had to be held back artificially.