They want government action to limit families to just two children and propose a crackdown on immigration to slash Scotland's population by a quarter.
But radical green group the Optimum Population Trust - branded "eco-fascist" by opponents - has now won the backing of some MSPs and will today stage a major conference at the Scottish Parliament.
Prominent supporters of the OPT include its patron, BBC naturalist Sir David Attenborough and scientist Dr James Lovelock, whose "Gaia" hypothesis suggests that the Earth is a single organism and humanity is destined to be wiped out unless it reduces environmental damage.
Government green adviser Sir Jonathon Porritt, who also briefs Prince Charles on environmental issues, is another top OPT figure.
...the OPT believes Scotland and Britain must do their part to stabilise the world's population, which could rise to more than nine billion within 40 years. They want the UK population to fall to as low as 30 million, with Scotland playing its part in the reduction.
On immigration, the OPT believes there should be a zero cap on net immigration, meaning numbers would be strictly limited to replace those leaving the country to live elsewhere.
Leading environmentalist George Monbiot is among the OPT's fiercest critics, claiming that global population increase "pales into insignificance when compared with the effect of increased consumption".
A recent paper by the OPT claimed that if couples had two children instead of three they could cut their family's carbon dioxide output by the equivalent of 620 return flights a year between London and New York.
One extra child causes a CO2 output of nearly equivalent to a return flight to New York everyday?
One source of figures suggests ; Individual CO2 emissions - 1 person per year in UK - 10000 kg C02
Return flight London - New York - 6886 miles - 3856 kg C02
But the claim was made in The Times May 6th 2007
Having large families ‘is an eco-crime’ - Times Online..according to a report to be published tomorrow by a green think tank.
The paper by the Optimum Population Trust (OPT) will say that if couples had two children instead of three they could cut their family’s carbon dioxide output by the equivalent of 620 return flights a year between London and New York.
The OPT briefing actually says:
A non-existent person has no environmental footprint: the emissions “saving” is instant and total. Given an 80-year ifespan and annual per capita emissions (2006) of 9.3 tonnes of CO2 (Defra, 2007, provisional), each Briton “foregone” – each addition to the population that does not take place – saves 744 tonnes of CO2, equivalent in emissions to 620 return flights from London to New York (1.2 tonnes of CO2 each). The Stern report estimates the social cost of CO2 at $85 per tonne: each foregone Briton therefore saves society $63,240 (c £30,000).
So the OPT may be silly, but not as silly as a Scotsman journalist who cut and pasted from a silly Times journalist.