ARCHIVAL (ABC NEWS, 8-26-19):MATT GUTMAN: The rainforest, the so-called lungs of the Earth. Much of it now choked in flames.

NARRATION: In 2019, images of the Brazilian Amazon on fire shocked the world.

ARCHIVAL (CBS NEWS, 10-06-19):MANUEL BOJORQUEZ: These large swaths of rainforest are chopped down to make way for cattle ranching and farming.

NARRATION: Today, the world is consuming more meat than ever. Americans, alone, put away over 50 pounds of beef per person each year. Its a habit that dates back decades.

ARCHIVAL (HARDEES COMMERCIAL):MAN: Only five miles to a Hardees big roast beef. WOMAN: Five miles?!MAN: What a sandwich. Tender, juicy

NARRATION: Its a habit that dates back decades.

ANNA LAPP (AUTHOR, DIET FOR A HOT PLANET): Ive been really looking into this history of what did Americans used to eat? What were we eating in the 1970s, and how has it changed? At the time there was this dominant message, a message which I think is still pretty dominant today, which is that our bodies need a significant amount of protein, and the best source of that protein is animal protein.

NARRATION: Author and environmental activist Anna Lapp is the daughter of Frances Moore Lapp who published Diet for a Small Planet in the 1970s. That book advocated a plant-based diet at a time when beef and dairy were king.

ARCHIVAL (NATIONAL DAIRY COUNCIL PUBLIC SERVICE ANNOUNCEMENT, 1973):COW: For a balanced diet, all four food groups are important everyday. But only the milk group has one sourceme. Or should I say Moooo.

ANNA LAPP: It was heretical. It was so threatening to the National Cattlemens Beef Association that they actually hired nutritionists to prove that her recipes were inedible.

NARRATION: Today, Anna Lapp argues that consumers should eat less meat because of the harm it does to the Earth. Nearly 80% of the worlds agricultural land is now used to graze or grow food for livestock.

ANNA LAPP: There are so many ways in which industrial beef impacts our planet, from water use to the impact on soil health, to the loss of biodiversity when were using so much land for just a couple of crops to feed livestock. Were talking about the energy used. The animal welfare implications. All this land, both grazing land, cropland, to produce an animal thats actually giving us a really inefficient return on our investment.

NARRATION: Lapp says it isnt just inefficient. Animal agriculture also leads to a byproduct known to impact global warming.

ANNA LAPP: You might have heard the fart jokes about cattle and climate change. Well its actually mostly burping. But theyre burping methane as part of their natural process. Well, that methane gas is a highly, highly impactful greenhouse gas.

ARCHIVAL (PBS NEWSHOUR, 8-8-19):NICK SCHIFRIN: Large-scale farming, along with the global consumption of meat and dairy, are fueling climate change in a way that could result in a food crisis.

NARRATION: A recent U.N. report on climate change and land urged reforms in how we use forests, grow crops, raise livestock. And how we eat. This, as alternatives to meat are having a moment.

ARCHIVAL (ABC-KGUN, 9-13-19):NEWS REPORT: Its the ultimate burger showdown. Meatless burgers, that is. Both contenders are plant-based.

NARRATION: Despite all the buzz, Lapp says convincing consumers that theres a connection between what we eat and the health of the planet can be a hard sell.

ANNA LAPP: I think that part of the reason why food was so invisible in the climate conversation is because it is such a complex system. You can almost see the emissions coming out of your tailpipe. You can picture, you know, why airplanes are so polluting. But your dinner plate doesnt seem like its a source of pollution, air pollution, climate pollution. How do you get people to understand that emissions occur all along the food chain?