In a study that's sure to stir up a fuss, a paper by the Optimum Population Trust in Britain indicates that having large families should be frowned upon as an environmental misdemeanour in the same way as taking frequent long-distance flights, driving an oversized vehicle and failing to reuse plastic bags. The study goes on to say that if couples had two children instead of three they could cut their family's carbon dioxide output equivalently to the amount of CO2 produced by 620 return flights a year between London and New York. Hmmmmm.... In a warming world it seems they may be on to something. John Guillebaud, co-chairman of OPT and emeritus professor of family planning at University College London, said that "The effect on the planet of having one child less is an order of magnitude greater than all these other things we might do, such as switching off lights. Then he goes on to point out that "The greatest thing anyone in Britain could do to help the future of the planet would be to have one less child." Now I'm betting that's not what a lot of people with large families want to hear, but the idea certainly is quite sound scientifically. And in a planet built to hold maybe a third of the current population comfortably it would seem to me that taking the whole concept of environmental sustainability into consideration when deciding whether to pursue personal parenthood on a grand scale has significant merit for us all.