The study was conducted by researchers at the University of Michigan and Tulane University and was commissioned by conservation group Center for Biological Diversity.

Gradually swapping out by 2030 half of all animal-based foods — including beef, eggs and dairy — for plant-based foods such as legumes and soy products could result in a 35% decrease in U.S. diet-related emissions, estimated the study. That equals a decline of roughly 224 million metric tons of emissions per year in 2030 — the equivalent of the annual emissions of 47.5 million passenger vehicles, said the researchers.

If U.S. beef consumption is also cut by 90%, the climate benefits could be even bigger, the analysis found.

That further-reaching change has the potential to bring about a 51% reduction in U.S. dietary-related greenhouse gas emissions (GHGE) by leading to a cumulative decrease of 2.4 billion metric tons of greenhouse gas emissions by 2030.

Those possible changes are due to the heavy carbon footprint of the average U.S. diet. From the study:

The total emissions associated with producing the average U.S. diet amounts to 5.0 kg CO2 eq. per person per day. Whereas red meat (beef, pork, lamb) represents 9% of the calories available from this diet, it contributes 47% of the GHGE. All animal-based foods combined (red meat, poultry, fish/seafood, eggs, dairy and animal based fats) represent 82% of the baseline diet GHGE.

"While a diet shift isn't a silver bullet, it could play an important role in curbing climate change," Martin Heller, lead author of the study and a research specialist at University of Michigan's Center for Sustainable Systems at the School for Environment and Sustainability, said in a statement. "This research shows that replacing only half of our animal-based food consumption with plant-based alternatives could account for nearly a quarter of the reductions necessary for the U.S. to meet a Paris Agreement target," Heller said.

The Trump administration formally withdrew from the global climate accord last year.

Stephanie Feldstein, population and sustainability director at the Center for Biological Diversity, said the study provided clear steps for how to rein in planet-heating emissions.

"Moving the American appetite from our burger-heavy diet to plant-based eating is a powerful and necessary part of curbing the climate crisis," she said. "The COVID-19 pandemic has exposed the meat supply chain's vulnerabilities, but our food system faces even greater long-term threats from climate change. We desperately need policymakers to support sustainable diets and a resilient food system."

To help that effort, the Center for Biological Diversity has also put out a policy guide outlining steps U.S. policymakers can take to successfully lower diet-related emissions.

At the federal level, the document states, the Dietary Guidelines for Americans should emphasize the importance of plant-based foods (including for protein), and urge reductions in meat and dairy consumption. At the municipal level, policymakers can enact policies to boost the "availability and acceptance of plant-based options."

"By bringing together food policy and climate policy," says the guide, "governments can provide a foundation for a healthy, climate-friendly food system."