21 September 2005Fiona Harvey
Global warming could reduce harvests and plant growth, with a serious effect on farm productivity, scientists will warn on Thursday.
The finding, based upon an examination of the effects of the 2003 heatwave in Europe, is of particular concern because many scientists previously assumed that global warming would increase plant growth, with beneficial effects for harvests and the environment.
In a study to be published on Thursday in the peer-review journal Nature, scientists from several European research institutes and universities found that the growth of plants during the heatwave was reduced by nearly a third.
In Italy, the growth of maize dropped by about 36 per cent. Oak and pine also grew much less, the study found, reflecting an overall reduction of 30 per cent in plant growth. Wheat crops, however, were less affected because of the timing of the heatwave and the accompanying drought, which saw mean air temperatures rise by as much as 6° Celsius above their long-term average and rainfall at half of the long-term norm. Climatologists say climate change will bring an increase in the frequency of heatwaves.
Apart from the effects on the harvest, the decline in the productivity of plants spells bad news for the environment as a whole. Greater plant growth means that plants are removing more carbon dioxide from the atmosphere. This would lessen global warming over time, because the climate is believed to be changing under the influence of a surfeit of carbon dioxide, a gas that traps heat in the earth's atmosphere. Human activity has caused this increase in the gas, which is produced when fossil fuels are burned.
The heatwave study follows experimental results from the US that show plants do not grow faster when there is more carbon dioxide in the atmosphere. Previous models of climate change had assumed a doubly beneficial effect from plants growing faster under warmer conditions, while there was more carbon dioxide available. If plants grow less during heatwaves, and fail to grow faster when there is more carbon dioxide present, scientists will have to revise their predictions of the likely severity of the effects of climate change. In another recent study, scientists at Cranfield University found that an unexpectedly large amount of carbon dioxide was released from the soil under warming conditions. This could raise the amount of carbon dioxide in the atmosphere, which many governments have been attempting to reduce.
http://news.ft.com/cms/s/e2b9c09c-2acd-11da-817a-00000e2511c8,ft_acl=,s01=2.html
