– Roger Martin is a former diplomat and leading environmentalist. He is now Chairman of the Optimum Population Trust. Any views expressed are his own –

I’ve been an environmental campaigner for 20 years, and can confidently summarise all our problems as ‘too many people consuming too much stuff.’ But in all those worthy meetings about all those worthy green projects, I’ve noticed that everyone talks about the stuff, like consuming less energy rather than providing more; and no-one talks about the people, the number of consumers.

So in the last 10 years I’ve been increasingly asking colleagues, ‘Can you name a single environmental problem that would not be easier to solve with fewer people, and doesn’t get harder –- and ultimately impossible –- to solve with ever more?’ No-one can. Optimum Population Trust (OPT) Patron Sir David Attenborough recently said he too had never encountered such a problem. Have you?

Here’s an interesting fact. OPT’s YouGov poll in June found, to my surprise and delight, that 70% of us are already aware that population growth here causes serious environmental problems; half of us would like a smaller UK population (England is already the most crowded country in Europe); and only 8% of us actually want any more population growth at all. So why is everyone so nervous of mentioning the P word? Why do our politicians try to “reassure” us that they, at least, are not worried by the prospect of our population rising by 20 more Birminghams in our lifetimes? OPT speaks, seemingly, for a silent majority.

Another fact — our planet is finite, it cannot support an infinite number of people, so population growth, caused by more births than deaths, will definitely stop one day. And when it stops, it will be because of either fewer births or more deaths (or some combination).

This will either by human, humane means –- contraception backed by policy which makes it readily available and encourages people to use it — or by the inhumane, natural means through which nature, as Darwin pointed out, has kept every other species in balance with its habitat for the last billion years or so –- famine, disease, and predation (in our case war). Which would you prefer? There is no third alternative of indefinite growth.

There is another fact which is very relevant to the climate change negotiations leading to the Copenhagen Summit in December. I am trying hard to get at least this fact recognised in the summit communiqué: All population growth increases the number of both carbon emitters (much more in rich countries than in poor) and future victims of climate change (more in poor countries than rich) and thus makes all the problems of “mitigation” (reducing emissions) and “adaptation” (coping with a warmer world) harder to solve.

Since the Kyoto Agreement was signed only 18 years ago, the number of emitters and victims has risen by some 1.3 billion people, and is still rising by 80 million per year, or 1.5 million per week, or 10,000 per hour. But no-one ever mentions it. Don’t you find that a bit surreal?

OPT’s groundbreaking report published last month, “Fewer Emitters, Lower Emissions, Less Cost” proved that it makes economic sense, as well as climatic sense, to invest a modest proportion of the climate change funds in meeting the unmet need for family planning. This would be nearly five times cheaper, per carbon ton saved, than putting it all into fancy green technology. A person who never existed, and all their descendants for ever, has a carbon footprint of zero.

And finally there’s the crying, shameful, humanitarian need which we go on ignoring, summarised poignantly by a devout woman, desperate for family planning, reported recently from the Philippines. She said: “If the Holy father could only experience for one hour what it’s like to be six months pregnant in a Manila slum, with seven children to feed and no money to feed them, he would change the doctrine on contraception the very next minute!” There are hundreds of millions like her.

As a UNICEF report said: “Family planning could bring more benefits to more people at less cost than any other single technology now available to the human race”.