"Nitrogen enrichment is pushing us towards a weedier world,' says David Wedin of the University of Toronto, Canada. Burning fossil fuel releases nitrogen oxides, which ecologists believe could act as fertilisers and promote luxuriant growth of weeds. This shift in vegetation could hinder the earth's ability to moderate global warming, Wedin warns. Ecologists hoped that exuberant plant growth would pull in more carbon dioxide (CO₂) from the atmosphere and put a brake on global warming. But long-term nitrogen enrichment would result in weedy plants adding less organic matter to the soil, which means they will pull less CO₂ from the air (New Scientist, Vol 152, No 2060).