Spring arrives a week earlier than in 1970s

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If you think spring seems early this year, you're right. The green shoots of regrowth now arrive a week earlier in the northern hemisphere than they did in the 1970s, according to analysis of satellite data.

While the news may be good for gardeners and sunseekers, it also provides the strongest indications that global warming, caused by the build-up of carbon dioxide from fossil fuels in the atmosphere, is well under way. The result could be calamitous changes in weather locally and globally.

Scientists at Boston University and the space agency Nasa compared satellite data which measured the amount of vegetation in the northern hemisphere from the period between 1981 and 1991 with that from the early 1970s. They found that plant regrowth after winter was happening sooner than before. Other figures have shown that the period since 1980 has been the warmest, in terms of global temperature, for the past 200 years.

The earlier plant growth is probably due to a combination of higher air temperatures and increased carbon dioxide.

But while increased vegetation will absorb some of the carbon emitted from consuming fossil fuels, it will not compensate for human-generated output, said Peter Cox, who is creating computer models of vegetation growth in global climate at the Hadley Weather Centre in Bracknell, Berkshire.

Professor Cox said: "Vegetation absorbs between 1 and 2 gigatonnes [thousand billion tonnes] of carbon at the moment, but that has to be compared to about 7 gigatonnes of fossil fuel output."

The researchers, whose work is reported today in the science journal Nature, said the effects of the "early spring" are not evenly spread, with central Europe, southern Russia and a broad region near Lake Baikal in Siberia the most affected. The changes are concentrated in the temperate areas of the hemisphere, between 45 and 70 degrees north.

The satellite data showed other indications that global warming is under way: a 10 per cent reduction in the length of winter snow cover from 1973 to 1992, and the earlier disappearance of snow in spring.

Professor Cox said that while the data might seem like good news, the effects of global warming were unpredictable. "The problem is that although the vegetation in high latitudes gains from the temperature and carbon dioxide, changes elsewhere - such as in the tropics and equatorial regions - will lead to a reduction in vegetation."

The one positive note is that the results agree with the computer models developed at Bracknell, suggesting that their projections for climate change are soundly based.

The Army has stopped using flares and tracer rounds on thousands of acres of Dartmoor because of the fire risk in tinder dry drought conditions.

The commander of Devon and Cornwall training areas, Lt-Col Tony Clark said units were not allowed to use tracer rounds, illuminating flares for night exercises, or anything likely to cause a fire.

The dry spell is worrying farmers in the area and the next week will be "critical" for farmers who have just sown crops.