By Gary Wockner

Millions of young Americans want to shrink their carbon footprints.

The best way for them to do so? Limit their family size. Having one fewer child can be up to 30 times more effective at cutting greenhouse gas emissions than the next-best action, "living car-free," according to a series of recent studies from the American Association for the Advancement of Science, the "Drawdown Project," and other academic papers.

These studies, coupled with heightening anxiety over climate change, have even spawned a global #Birthstrike movement. Across the world, young people are realizing that the planet simply can't sustain endless population growth.

However, these reports, as well as #Birthstrike members themselves, often overlook the science behind who actually emits the most greenhouse gases -- and therefore whose population growth needs to be curbed.

Point blank: Citizens in developed countries, especially here in the United States, emit dramatically more greenhouse gases than citizens in developing countries. The Union of Concerned Scientists reports that the average American produces five times more greenhouse gases than the average Mexican and ten times more than the average person in India.

This excessive consumption -- and the rampant materialism that fuels it -- is depleting our natural resources. Household consumption contributes to "more than 60% of global greenhouse gas emissions and between 50% and 80% of total land, material, and water use," according to a recent study published in the Journal of Industrial Ecology. A report by the Sierra Club indicates the average American consumes 35 times more natural resources than the average person in India and 53 times more resources than the average person in China.

And the Center for Global Energy Policy at Columbia University published a report indicating that population growth necessitates reliance on high greenhouse gas-emitting energy sources for new construction of buildings, roads, and other infrastructure -- all of which is far more intensive in the United States and other developed countries.

Simply put, if we want to curb greenhouse gas emissions and stop depleting our natural resources, we should focus on limiting population growth in industrialized countries, especially the United States.

America is adding people at a rapid pace. The population has grown by 72 million people since 1965, according to Pew Research. And we'll add another 100 million people by the year 2065, almost solely due to immigration.

Nearly all immigrants come from countries that have far lower greenhouse gas emissions rates. But once they arrive here, most adopt the prevailing American culture of ravenous energy consumption and consumerism, causing greenhouse gas emissions to soar.

It's time we look in the mirror and quit ignoring the devastating, planet-destroying impacts of America's population growth.

Gary Wockner, PhD, is an environmental activist in Colorado specializing in river protection, climate change, and population stabilization. Web: GaryWockner.com Twitter: @GaryWockner