An interesting little aside:
The fact that leaves are turning brown later each autumn is caused by rising levels of carbon dioxide in the atmosphere and not global warming, British scientists have discovered.
Over the past 30 years autumnal senescence, the process of plant ageing by which leaves discolour then fall, has been delayed in Europe by between 1.3 and 1.8 days a decade. Trees have also been growing leaves earlier. During this time atmospheric CO2 has risen by 13.5 per cent.
See? CO2 really is plant food.