Environmentalists should be worried about Canada's fertility rate. It's too low. We need to make more babies. It's the green thing to do. This will not be immediately evident to environmentalists, to say the least. In fact, I can say with some confidence that to the extent environmentalists worry about fertility rates at all, they want fewer babies, not more, because they believe this will reduce the burden humanity puts on the environment. I know this because every time I write a column advocating policies that would boost fertility rates I get a deluge of e-mail from environmentalists accusing me of crimes against Gaia. This column is my defence. It is also a plea to environmentalists to broaden their understanding of what it takes to protect that which they love. Let me start with an amazing fact: In 1989, when anthropogenic climate change was not much more than a debatable hypothesis, 35 per cent of Americans told Gallup they worry a "great deal" about it. In the years that followed, evidence accumulated. In 2005, the world's national science academies issued a joint statement saying "climate change is real" and the facts are "sufficiently clear to justify nations taking prompt action." And yet, at the beginning of this year, only 28 per cent of Americans told Gallup they worry about climate change. Now, there are many reasons why Americans aren't more concerned about climate change, but a big one is the economy. When it struggles, concern for climate change falls; when it does well, concern rises. The middle years of the last decade seemed pretty good in economic terms and in 2007 concern for climate change hit a peak of 41 per cent. Then the American economy crashed -- and so did concern for climate change. It's the same story in Canada. When the economy boomed, support for action on climate change soared. In 2007, Canadians chose it as their top concern, ahead of the economy, health care, and all the rest. And just like that, Stephen Harper got religion. Climate change wasn't mentioned in the Conservatives' 2005 election platform, but in 2007 Harper declared it is "perhaps the greatest threat to confront the future of humanity today." Bold action was promised. But then came the global economic storm of 2008 and the recession of 2009. In a flash, climate change ceased to be Canadians' top concern. And Stephen Harper stopped promising bold action. The lesson from this evidence -- and heaps more like it -- is that good environmental policies will not happen without public support. And public support will not happen without a strong economy. So what's this got to do with the fertility rate? Glad you asked. The connection is population aging. On average, Canada -- like all developed countries -- is getting older. The proportion of society that is young is declining rapidly at the same time the proportion made up of old folks is growing. The primary cause of population aging is low fertility. It takes an average of 2.1 babies per woman merely to maintain a population, and Canada's fertility rate, like that of most developed countries, has been well below 2.1 since the 1970s. It is currently 1.6. As a result of baby boomers not replacing themselves, the population will age considerably over the next couple of decades and, if nothing changes, it will start to shrink later in the century. Good, say many environmentalists. Fewer people equals less of a burden on Gaia. Unfortunately, no. The demographic shift means the ratio of workers to retired people will steadily worsen. In 2005, the retiree population was 20 per cent of the size of the working-age population. Over the next several decades, it will become 40 per cent. By mid-century, there may only be two workers per retiree. The economic ramifications are huge, which explains why economists are really, really worried. As former Bank of Canada governor David Dodge noted in a recent speech -- which I will keep quoting unless ordered to stop, dammit -- we'll need huge gains in productivity just to keep our collective head above water. "If we fail to increase labour productivity from the miserable one per cent a year average since the 1970s, we will condemn ourselves to a standard of living which is in decline relative to the rest of the world this decade and in absolute decline next decade." Some greens shrug off talk like that. We'll still be prosperous even if our living standards decline somewhat, they say. So what if people have to forgo that giant-screen TV? We'd be better off with less stuff. And so would the environment. Maybe on some philosophical plane they have a point but not in the reality where the rest of the population lives. When people feel they are getting poorer, and their children may be poorer still, their priorities change in a hurry -- and the first thing they jettison is concern for the environment. So what can we do? No, the answer is not a baby boom. Even if it were desirable to boost fertility rates to 3 or 4 -- and it's not -- public policy cannot make that happen. But it can, with a little luck, raise fertility rates from 1.6 to, maybe, 1.9 or 2.0. Even with that boost, and even with further large-scale immigration, population growth would slow, then stop. And over the very long term we'd likely start into a decline. But that modest change would ease the strain of population aging, and it would make the transition from a growing population to a stable or declining population slow and gentle. And that would protect the economic health on which environmental health depends. Want to save Gaia? Have another baby.