It has been the mildest winter on record on our shores so far, but forecasters are warning that the warm weather is about to end as an intense cold front moves south into Britain from the Arctic. Conditions that let daffodils and rhododendrons flower in December and allowed squirrels to fatten themselves on easily accessed acorns are about to end.

The news will disappoint some – including UK farmers who had hoped to fill the shop shelves with homegrown asparagus in a few weeks – but for others the cold conditions are likely to bring relief. These include the nation’s fruit growers as well as native birds, for which prolonged mild weather in winter can have worrying consequences.

“There were winners and losers with the onset of the mild weather,” said David Buckingham, the senior conservation scientist with the RSPB. “Equally there will be some who gain more than others when it ends.”

Take the nation’s butterfly and moth lovers. They have just experienced an unprecedented festive season observing winged insects that have barely visited Britain until this winter. Examples include Cornifrons ulceratalis, which normally frequents the Canary Islands, Portugal and Greece, but which has just turned up in moth-watchers’ traps all along England’s south coast. “It had never been seen before in the UK but has appeared several times this winter,” said Richard Fox, of Butterfly Conservation. “It is absolutely amazing.”

Other moth visitors include Syncopacma polychromella, normally an inhabitant of the Mediterranean and the Middle East, and the Levant Blackneck, from north Africa. They have made only a few previous visits to the UK until this winter, when dozens of sightings were recorded.

“Some of these moths have never been seen in Britain before, while those that had made previous visits did so in summer,” added Fox. “The really incredible feature about these recent forays to our shores is that they have occurred in winter, thanks to strong southerly winds and extremely mild conditions. Unfortunately the forthcoming cold spell is going to bring an end to our extended Christmas.”

By contrast, the prospect of a cold snap is more likely to be appreciated by the nation’s gardeners and fruit farmers because a continuation of the current mild weather would pose serious problems for growers of apple and pear trees and blackcurrant bushes, said Guy Barter, of the Royal Horticultural Society.

“If the mild weather were to continue for much longer, then there would be a danger that the nation’s fruit trees would flower too early – in March or April – when they would then be vulnerable to a sharp frost that would destroy their blossom. And, of course, if that were to happen, they would bear no fruit.

“In addition, if apple, pear or blackcurrant plants were to flower early, they may do so at a time when there were few bees about and so they would not be pollinated. A cold spell that would return fruit tree flowering to its normal season is therefore to be welcomed by most farmers and fruit growers.”

This point was underlined by Lee Abbey of the National Farmers Union. “The mild winter has encouraged some plants to flower early, and others to reach maturity at a time when consumer demand has not reached its peak. There are also challenges with crops in storage, particularly those that rely on ambient temperatures to preserve their quality. On the other hand, UK growers are experienced in dealing with unusual weather patterns.”

In fact, the entire food chain can be affected by unusual weather conditions, a point stressed by Buckingham. “It may sound paradoxical, but mild weather can often produce dramatic reductions in insect populations. Very cold weather kills off viruses and bacteria in the soil whereas in mild weather they thrive. They then infect and kill off large numbers of insects, including native species of butterflies and moths.

“Their numbers drop, and that has consequences later in the year when native birds, such as wrens and goldcrests, do not have enough food to feed their chicks – which then starve. Prolonged mild weather can have unexpected and pervasive effects.”

Winners and losers as warm weather ends



Winners

Otters Lower river levels in drier, colder weather mean they won’t seek food on land and risk death on the roads.

Fruit farmers The appearance of early blossom will be delayed, reducing the risk of crop losses.

Wrens and goldcrests Viruses and bacteria will be less likely to kill off the insects on which they prey.

Losers

Cornifrons ulceratalis moth A stranger to the UK until this winter, it survives here only in mild weather.

Squirrels The rodents have become used to gorging on easily available acorns and other foods.

Asparagus farmers The mild weather held the promise of early bumper crops.