(CNN)An environmental campaign group has called on Pope Francis to take up veganism for Lent, in exchange for $1 million donated to the charity of his choice.
Genesis Butler, a 12-year-old US animal rights activist, and the Million Dollar Vegan campaign released an open letter to the Pope, who has made climate change a central concern of his spiritual leadership over the world's 1.2 billion Catholics.
"I write to you today with the utmost respect and appreciation for your speaking out on climate change, habitat loss, and pollution, and for reminding the world that Earth is a home we all share," Butler wrote in the letter, which was published in national newspapers around the world.
Butler cited Pope Francis's 2015 encyclical "Laudato si," in which he called for "changes of lifestyle, production and consumption" to protect the environment. Climate change, he said, "represents one of the principal challenges facing humanity in our day," and will disproportionately affect the world's poorest people.
Studies have indicated that switching to a plant-based diet is one of the most effective methods of minimizing one's environmental impact. Livestock farming, as Butler noted, is responsible for 14.5% of global greenhouse gas emissions, while the production of animal products commands about 83% of farmland worldwide, but contributes only 18% of our calories.
"With 815 million people suffering from malnutrition, imagine how many hungry people we could feed across the world if we moved away from such wasteful foods," she said.
From Long Beach, California, Butler turned vegan at the age of six and subsequently began to advocate for animal rights. At 10, she gave a TED talk on the environmental impact of consuming animal products.
Million Dollar Vegan, supported by celebrities including Paul McCartney, Woody Harrelson and Mena Suvari, promotes veganism as a means of tackling world hunger, climate change and animal suffering.
"Moving towards a plant-based diet will have substantial environmental benefits. It will protect our land, trees, oceans, and air, and help feed the world's most vulnerable," Butler wrote. "We need to take action, and we need the support of influential leaders like yourself."
This year, the Christian period of Lent begins on March 6 and ends on April 18. If Pope Francis accepts Butler's challenge, $1 million will be donated to his selected charity by the Blue Horizon International Foundation, a US non-profit that aims to "accelerate the removal of animals from the global food chain."
The Vatican has not yet responded to CNN's request for comment.