One of the world's most influential climate activists, Swedish teenager Greta Thunberg, has done everyone a big favour by zeroing in on the root causes of the crisis that threatens humanity's future.

"The richest 10 percent of the world's population emits about half of our emissions of our greenhouse gas emissions," she said in a recent speech. "The richest one percent emits more than the poorest 50 percent."

She pointed out that a relatively small number of companies are responsible for the majority of greenhouse gases.

Thunberg also noted that it's not people in places like Mozambique, Bangladesh, or Colombia who are most responsible for the extreme weather events that sometimes ravage their countries.

Rather, it's those who are rich and who often fly around the world, sometimes in private jets, and who are voracious consumers.

That's why it's facile to suggest that containing global population growth is an efficient way to reduce emissions.

Curbing the birthrate would only have a significant effect on the climate if it occurred in wealthy nations.

That was demonstrated by a 2017 study published in Environmental Research Letters.

It concluded that having one fewer child in developed countries would reduce 58.6 tonnes of emissions of carbon dioxide equivalents per year. This figure factored in offspring that result from that child being born.

Pipelines are far more dangerous than babies

To provide context, British Columbia's total emissions in 2016 were 62.3 million tonnes of carbon dioxide equivalents.

The Trans Mountain pipeline expansion's contributions to emissions will likely exceed that. A City of Vancouver study estimated its downstream impact at 71.4 million tonnes of carbon dioxide equivalents per year.

So stopping a pipeline would have a far greater impact on the planet than not having a child.

Living car-free, on the other hand, would save 2.4 tonnes of emissions per year, and eating a plant-based diet would save 0.82 tonnes per year, according to the study in Environmental Research Letters.

Avoiding one flight across the Atlantic or Pacific oceans would prevent 1.6 tonnes of emissions, the researchers concluded.

It's something to consider as the United Nations is about to mark World Population Day on Thursday (July 11). It focuses attention on the urgency of this issue.

Thunberg has been devoting a great deal of attention to air travel.

According to the Air Transport Action Group, flights generated 859 million tonnes of carbon dioxide equivalents worldwide in 2017. Overall, humans generated more than 40 billion tonnes of emissions that year.

But population growth is still an important topic for discussion, even though it's scrupulously avoided by some environmental journalists. 

That's because the United Nations has forecast that the global population will exceed 11 billion by the end of the century. (Others dispute that figure, including Canadian authors John Ibbitson and Darrell Bricker, who are predicting a decline in the global population.)

The areas between the tropics of Cancer and Capricorn are being hit especially hard by the climate breakdown. That, in turn, is triggering migration from areas of rapid population growth to places like Europe and the United States. And that's resulted in a backlash against refugees, which is being promoted by right-wing politicians like Donald Trump and Nigel Farage.

Millennials grapple with having kids

According to the United Nations, Niger, Somalia, the Democratic Republic of Congo, Mali, Chad, Angola, Burundi, Nigeria, Gambia, Burkina Faso, and Uganda all had birthrates exceeding five children per woman in 2017.

South Korea, on the other hand, only had a fertility rate of 1.11 children per woman, ranking 200th in the world.

Canada was in the 174th spot at 1.525 children per woman, whereas the United States was slightly higher at 1.886 children per woman.

A fascinating 2013 book by Alan Weisman, Countdown: Our Last Best Hope for a Future on Earth?, looked at countries individually and showed remarkable diversity in how they were addressing the birthrate.

Those that were promoting girls' education showed greater declines.

There were also some surprises—clever family planning, for instance, curbed the birthrate in Thailand. In Japan, married women told Weisman that they stopped having sex with their husbands to reduce the likelihood of becoming pregnant.

In western industrialized countries, there's a growing movement to launch conversations about the difficult decision over whether to have children in the midst of a climate crisis.

U.K.-based BirthStrike's website features declarations by people who are refusing to have children because of the magnitude of ecological problems.

A U.S.-based group, Conceivable Future, promotes a more nuanced approach, describing the challenges posed by climate change as a "reproductive justice crisis".

"How do you protect your health and your children in an increasingly dangerous and toxic environment?" it asks. "How do you decide whether or not to have a baby when a healthy and stable future is increasingly jeopardized? Even with access to fertility regulation, no one makes reproductive ‘choices’ freely in the face of so many economic and environmental pressures." 

Conceivable Future is demanding the right for women to make reproductive choices "free from massive, avoidable, government-supported harm". And it also wants an end to fossil-fuel subsidies.

In addition, Conceivable Future posts videotaped testimonials of women offering their thoughts about having children in the face of monumental ecological challenges.

Parents at forefront of climate activism

This movement to discuss this issue gathered momentum earlier this year when Congresswoman Alexandria Ocasio-Cortez declared that it was a "legitimate question" whether it's okay to have children.

"There's scientific consensus that the lives of children are going to be very difficult," the New York City politician stated.

That triggered a predictable firestorm from right wingers, who've been the most obstinate in denying the magnitude of the climate crisis.

At the same time, it's often parents who are at the forefront of climate activism because they are so freaked out about the world that their children will inherit.

To cite one example, Canadian writer Naomi Klein became a much more forceful climate activist after the birth of her son in 2012. Two years later, her landmark book, This Changes Everything: Capitalism vs. Climate, was released.

The most climate-conscious mayor in Vancouver's history, Gregor Robertson, has three children and he and his ex-wife were foster parents to a fourth.

Canada's greatest champion for climate solutions, David Suzuki, has five children and six grandchildren. Among his 52 books are 19 for children.

One of America's most outspoken climate educators, former vice president Al Gore, has four children.

So it's not so simple as equating having no children to being a climate hero. However, that's not to deny some millennials are refusing to procreate for that very reason.

It's much more complicated than that. And if we're going to collectively address this situation and stave off disaster, it calls for a nuanced approach.

It's necessary to be fully conscious of all the factors that got us here in the first place.

And it requires an awareness of what's most likely to lead to devastating losses of human life and other species.

For example, there's a risk of large methane releases from melting permafrost on the Arctic.

That would sharply increase the atmosphere's capacity for trapping heat—far, far more than bringing one child into this world.

The methane issue is one of the lesser-covered concerns, in part because these emissions are not factored into climate models.

Individualizing responsibility lets capitalism off the hook

Another potential feedback loop that has received even less attention is the effect of global warming on soils.

A 26-year study at the Harvard Forest in Massachusetts found that higher temperatures could result in significantly larger releases of carbon in the first 10 years.

Then there's the risk of ocean acidification leading to the release of large amounts of carbon dioxide from the seas.

It's often said that world has 12 years to take action to avoid a climate catastrophe, according to United Nations Intergovernmental Panel on Climate Change.

Not having kids is one option for people in rich countries to take individual action to curb emissions. But it's not the only choice.

As Vancouver writers Am Johal and Matt Hearn noted in their book, Global Warming and the Sweetness of Life, "individualizing responsibility for eco-collapses is one of contemporary capitalism's prime defensive strategies".

“Blaming the choices individual people make in the context of highly limited options and grinding employment pressures is a fool’s errand,” they wrote.

It can also sometimes smack of classism.

This is especially so when those in rich countries are looking down their nose at those in poor countries who see having more children as their only economic lifeline for survival.

Climate change is complicated. To grapple with its reality, we need to be open-minded, curious, and compassionate. Otherwise, we risk a slide into tyranny.