While the US government faffs around pretending climate change is neither real nor important, the rest of the world is getting on with fighting against it. Although the actions of administrations, states, cities, and business are making a major difference, the behaviors of individuals are important too.

We’ve argued in the past that the most valuable thing you can do for climate advocacy is to vote for politicians that are pro-science and pro-environment. There are plenty of other things you can do too, but as highlighted in the journal Environmental Research Letters, the best courses of action are often rarely reported about.

This may not be surprising, however, as they tend to be things people are involved with in their everyday lives: living without a car, avoiding air travel, avoiding eating meat, and – most “controversially” – have fewer children.

The logic behind these choices is simple. Everyone in industrialized nations can abide by these actions, and they would clearly reduce the amount of greenhouse gases in the atmosphere. Farming animals is very energy-intensive; plants, less so. Air travel and cars use a lot of carbon-rich petrol, so walking or cycling or using public transport would cut this out dramatically.

Finally, having fewer children means the next generation would require (and demand) fewer resources. The planet is already struggling to meet our needs and desires as it is, and children in wealthy nations use a disproportionate amount of resources compared to children elsewhere.

Lund University researchers looked through a wide range of studies focusing on climate change mitigation, and found these four actions do more than anything else. Living car-free saves 2.4 tonnes of CO₂ per year, for example, and a plant-based diet saves 0.8 tonnes.

Having just one less child saves a remarkable 59 tonnes of CO₂ per year. This is 295 times more effective than regularly recycling, or 590 times more effective than using energy-efficient lightbulbs. If you can do these too, then by all means go ahead – but having smaller families makes the biggest difference by far.

“We recognize these are deeply personal choices," study co-author Kimberly Nicholas, a senior lecturer in sustainability at Lund University, said in a statement. But we can't ignore the climate effect our lifestyle actually has."

“It's especially important for young people establishing lifelong patterns to be aware which choices have the biggest impact.”

The most comprehensive analysis of climate change solutions to date was arguably published just recently in a book named Drawdown. The possible solutions were ranked in terms of their ability to sequester atmospheric carbon dioxide, and in terms of how much money the schemes would save by 2050.

The top 10 solutions, like this study, also feature a plant-rich diet (#4 out of 100) and family planning (#7). However, air travel comes in at #43, and mass transit comes in at #37. Electric cars make an appearance at #26.

The slight discrepancies are partly due to this book’s focus on both individual action and that of a larger collective, like a state or national government.

In any case, it’s hard to argue that having fewer children – or, alternatively, giving women more access to contraceptives – is not an effective action individuals can take to combat climate change. This is perhaps most important in countries with high birth rates, which today tend to be developing nations.

By investing more in the education (and empowerment) of women, and making sure access to contraception is guaranteed for all demographics, the world could save a whopping 120 billion tons of CO₂ by 2050 – more than any other method to push back against climate change, by far.