Severin Carrell

It is a discovery which should delight Britain’s gardeners: by 2050 spring will start before Valentine’s day (Feb. 14). Cherry and pear trees will blossom in late January, while flower beds will be crowded with blooming buttercups, irises and geraniums long before winter has officially ended.

A study on the impact of our warming climate has found that in 40 years’ time across most low-lying coastal areas of the globe spring will begin for many plants at least a month earlier than it does now and end several weeks later.

The predictions are based on a detailed study of plant records from the Royal Botanic Garden in Edinburgh (RGBE) dating from 1850, and weather records for Edinburgh dating back to 1775.

Malcolm Clark, of Monash University, Australia, and Roy Thompson, at the University of Edinburgh, who studied the records, confirmed that the “botanical calendar” had altered for scores of plants in the RBGE collection — plants that are now flowering earlier as average air temperatures slowly but steadily rise.

The most affected plants, they say, are ornamental cherries, peach and pear, as well as anemones, saxifrage, irises and perennials such as three-leaved bittercress. They warn that an ever earlier spring is likely to create significant problems for the plants, for birds and insects relying on them, and for farmers. As flowering plants move out of step, or “desynchronise,” with normal seasons, serious problems could emerge with the pollination. Plants could flower before the birds and insects that feed on them or the mammals that carry their pollen are at large. Most animal behaviour is guided by the length of the day rather than temperature.

The scientists believe that the places worst affected by the warming temperatures will be the low-lying coastal parts of the world and regions with maritime climates, such as the British Isles and western Europe, the Atlantic coast of north America as far south as Florida, Chile, New Zealand and north Africa.

Contested

The start of spring is already contested. Traditionally it starts with the vernal equinox on March 20 or 21 and ends with the summer solstice on June 21, but for statistical and record-keeping purposes the Met Office states that spring starts on 1 March and ends on May 31. With continued global warming these dates are likely to become less meaningful.

In maritime areas, for every 1{+0}C of warming flowers will bloom as if spring had begun 16 days earlier and ended 11 days later. According to widely accepted predictions that the world’s climate will warm by at least 2{+0}C by 2050, leading to warmer winters, spring in the British Isles will start in late January, and then finish in late June.

In continental regions, further from the warming effects of the oceans, the impact will be lessened but still significant, with the flowering starting seven days sooner and ending 11 days later for every degree of warming. — © Guardian Newspapers Limited, 2009