Should doctors advise people to limit the number of children they have for the sake of the environment, asks the latest bmj.com poll. Our decision to ask this question was triggered by a huge amount of weekend coverage of the editorial by John Guillebaud and Pip Hayes: Population growth and climate change.  Scotsman columnist Gerald Warner accuses doctors of being conscripted into the bogus “man-made” global warming hysteria who should stick to the day job instead of being missionaries for “progressive dogma.”

Lewis Page takes a similar line on www.theregister.co.uk. “Are babies really the same as patio heaters?” he asks, adding: “How would the doctors like it if barristers started handing out prescriptions, or accountants took to offering minor surgical operations? Maybe the docs should leave the eco advice to climate scientists or someone like that.”

But professions can and do wade into each other’s territory, of course. Just yesterday, Chief Rabbi Jonathan Sacks told Anglican bishops attending the Lambeth conference that religions should face the challenge of environmental disaster. I don’t read anybody urging him to stick to the day job and leave global warming to scientists and politicians.

I gleaned a sense of the reaction to the BMJ editorial before I left work on Friday evening when a colleague spotted Nicholas Lezard’s “No kidding, BMJ” blog in the Guardian.  Nicholas cited Homer Simpson’s lament: “I have three children and no money.  Why can’t I have no children and three money?”

But the editorialists weren’t advocating that people limit the number of children they have for economic reasons. Their argument is that there’s a clear link between world consumption of fossil fuels, fresh water, crops, fish and forests, and world population, (now standing at more than 6700 million).

Is it not worth looking at the economic argument for a moment? A survey last month found that the UK’s credit-crunched  parents could spend £186,032 on raising a child from birth to the age of 21, up by 33% in five years. And by 2012, it could increase by 42%, to more than £265,500. That’s presumably before you’ve even forked out family tickets for that year’s London Olympics.

The cost of raising children, or the environmental impact of having them, (perhaps both, in fact), may not be lost on modern UK Catholics. Forty years after the publication of Pope Paul VI’s Humanae Vitae  encyclical, it seems that lots of them are ignoring its ban on artificial birth control.

A survey of 1500 Mass-going Catholics in England and Wales for Catholic weekly The Tablet  finds that more than 60% of those aged between 18 and 45 have used condoms, and more than 42% have used the pill.

Instead of families now taking up a whole pew (not uncommon in the 60s and 70s), Tablet editor Catherine Pepinster writes that she now sees smaller, more affluent family units.

I personally find that rather sad. As the youngest of five, I know first hand the real-time soap opera that comes with having a batallion of brothers, sisters, in-laws past and present, nephews, nieces, and their offspring. I’ve never envied children with a paucity of siblings (although a bedroom of one’s own would have been nice), particularly when you have ageing parents to watch out for. When there’s more of you, you can share the load.

But back to the bmj.com poll, which is about the environmental, rather than economic cost, of having children. As I write it’s a close-run thing, with 53% saying that no, doctors should not be advising people to limit the number of children they have for the sake of the environment. Last night a similar figure thought the opposite. So don’t forgot to vote, after reading the editorial, of course.

David Payne is editor, bmj.com