If you were proud of yourself conscientiously recycling on your drive back home after picking up your kids from school - forget it!

A new study has identified the most effective ways to reduce our carbon footprint. Having one fewer child is the number one, followed - way behind - by living car-free.

If we rarely hear about having fewer children, but often about recycling, this mainly due to misrepresentations in government advice and school textbooks, the study shows.

But once we know what to do to reduce our climate impact, the question remains: how to do it. Biking instead of driving a car is a relatively easy lifestyle switch compared to deliberately deciding to have fewer children.

Industrialized countries play a major role in cutting carbon emissions and reducing global warming. But fertility rates in these countries are already low, alarmingly so for many governments. Yet, this is also key for sustainability.

Discuss.

Your child in tons of C02

In industrialized countries, one person could save 2.4 metric tons of CO2 a year living car-free, 1.6 from avoiding a single trans-Atlantic flight and 0.8 by changing to a vegetarian diet, researchers have found.

But having one fewer child blows those figures out of the water, with a reduction of more than 58 tons of carbon emissions per year.

This might be an uncomfortable result for many - but the data doesn't lie.

"Many people ask me what they can do to stop climate change," Kimberly Nicholas, co-author of the study told DW. "And I just wanted to give them answers."

Nicholas emphasized that she did not want to tell people what to do with such a personal decision as having kids. "But the data tell us that these four actions all have a big impact on the climate."  

Are fewer children the solution?

Nicholas' findings revive a controversial debate. In a world of increasing human population but limited resources, the challenge of sustainable development increases daily.

The think tank Club of Rome garnered serious criticism in 2016 after promoting the idea of a one-child policy for industrialized countries in a book called "Reinventing Prosperity."

According to the authors, such a drastic measure is a necessary part of a strategy to achieving economic growth, reducing unemployment and inequality, and addressing climate change.

A child born in an industrialized country consumes 30 times more resources than one in India - which for the authors was a fair justification to support a one-child policy. They suggested incentivizing women to give birth to only one child with a financial reward.

But for Reiner Klingholz, chairman of the Berlin Institute for Population and Development, this is pure nonsense.

The average number of children needed for a stable population is 2.1 - but the average fertility rate in Europe is already as low as 1.5. In countries like Portugal, the average is even lower - only 1.1 children.

"In countries like Portugal, a further reduction in fertility rates would result in social disasters," Klingholz said.

It could destabilize the economy.

Focus on Africa

An extremely high population growth in Western Asia and Africa is a major hindrance for sustainability. But this is not the case for industrialized countries, Klingholz believes.

"The rich part of the world does not live sustainably due to its high consumption and emissions," he said.

The right move in Klingholz's mind would be to reduce the carbon footprint of industrialized countries through a change in our lifestyle while supporting development in Africa that reduces fertility rates there.

Europe successfully reduced unsustainable fertility rates "only through education and development," Klingholz said.

The difference between the birth rate of educated and non-educated girls in some African countries is astonishing.

In Ethiopia, for instance, women who manage to finish a secondary-level education have an average of 1.3 children - and 5 if they lack schooling. In Nigeria, the difference is from 3.9 versus 6.7.

Education is the solution!

This is in fact the same line Nicholas supports. Having children or not wouldn't be as much of a controversy if we could manage to strongly reduce emissions through a car-free life, a plant-based diet, and a combination of all the other sustainable practices the study recommends, she says.

"If we make those changes and succeed in reducing emissions at the challenging level we have to, the impact of a person would be much smaller," Nicholas said. "This would push our societies in the right direction."

With that aim, they are encouraging governments and educational institutions to adapt their content and further motivate people to take action.

"They must make clear that recycling is a good start, and it is worthy - but there is much more to be done to save the planet," Nicholas said.

Now, it is up to each person to decide how they will start.