杏吧原创

ALMOST one-quarter of nature鈥檚 resources are being gobbled up by a single species, and it鈥檚 not difficult to guess which one. Based on figures for the year 2000, the most recent available, humans appropriate 24 per cent of the Earth鈥檚 production capacity that would otherwise have gone to nature.

The result is a gradual depletion of species and habitats as we take more of their resources for ourselves. Things could get even worse if we grow more plants like palm oil and rapeseed for biofuels to ease our reliance on fossil fuels.

鈥淭hings could get even worse if we grow more plants like palm oil and rapeseed for biofuels to ease our reliance on fossil fuels鈥�

That is the message from a team led by Helmut Haberl of Klagenfurt University in Vienna, Austria. Haberl and colleagues analysed UN Food and Agriculture Organization data on agricultural land use in 161 countries covering 97.4 per cent of farmland.

By comparing carbon consumption through human activity with the amount of carbon consumed overall, Haberl鈥檚 team found that humans use some 15.6 trillion kilograms of carbon annually. Half was soaked up by growing crops. Another 7 per cent went up in smoke as fires lit by humans, and the rest was used up in a variety of other ways related to industrialisation, such as transport (Proceedings of the National Academy of Sciences, DOI: ).

Haberl says that the Earth can just about cope if we meet future needs by producing food more efficiently. This could be done by intensifying agriculture on roughly the same amount of land as we use now. But we鈥檙e asking for trouble, he says, if we expand production of biofuels, as the only fertile land available is tropical rainforests.

鈥淚f we want full-scale replacement of fossil fuels by biofuels, this would have dramatic implications for ecosystems,鈥� says Haberl. He warns that some projections foresee four or fivefold increases in biofuel production. 鈥淭his would at least double the overall amount of biomass harvested, which is about 30 per cent above ground at present, but would increase to 40 or 50 per cent to meet these biofuel targets,鈥� he says.

This would mean clearing what remains of the world鈥檚 rainforests in countries such as Brazil and Argentina. As well as wiping out thousands of species, this would have devastating effects on the climate, he says. Unlike farmland, forests help to seed rainfall because they have high evaporation rates.

鈥淭he less evaporation there is, the less rainfall there is and the whole system dries up,鈥� he says.