At least 43 members of Congress have signed on to support a Green New Deal, a proposal championed by freshman Rep. Alexandria Ocasio-Cortez, D-N.Y., aimed at making the United States carbon neutral.

As climate change discussions heat up, however, one key greenhouse gas contributor is often overlooked: animal agriculture.

Data varies on equating animal agriculture's impact on climate change, but most studies place it in the top two contributors to greenhouse gas emissions — often listed directly behind fossil fuels, and sometimes ahead.

Rory Kraft, a coordinator of the sustainability and environmental studies minor at York College, said animal agriculture makes up 9 percent of greenhouse gas emissions.

"Tackling that 9 percent might be much more effective than anything else that you do," he added.

The sustainability and environmental studies minor focuses on a range of topics, including the impact of fossil-fuel dependency and considerations of climate change across the globe, according to the York College website.

The livestock sector represents 14.5 percent of all human-induced greenhouse gas emissions, according to the Food and Agriculture Organization of the United Nations. About 40 percent of those emissions are in the form of methane, and the remainder is split almost equally between nitrous oxide and carbon dioxide, according to the FAO report.

A draft proposal of the Green New Deal on Ocasio-Cortez's website makes note of needing to change the agriculture industry. The draft scope states the legislation will aim to decarbonize manufacturing, agriculture and other industries.

Still, the focus remains on minimizing fossil fuels, despite factory farms emitting large amounts of methane — a heat-trapping gas about 30 times more potent than carbon dioxide — and industrialized farming methods decreasing carbon-capturing patches of land.

"It's hard, I mean it's left out and it's the cause that all of us bear in some ways," Kraft said. "In all of these discussions the thing to remember is that the biggest producers of ... pollution or greenhouse gas is industry."

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York's factory farms: Conventional farms are common throughout the nation, and York County has one of the highest density levels of factory farms, according to factoryfarmmap.org, which uses data collected by the U.S. Department of Agriculture Census of Agriculture.

York County had 2,171 farms, and the average size of each was 121 acres — totaling 262,062 acres of land, according to the 2012 census.

Per site, there was an average of 765 cattle, 2,950 hogs and 135,692 broilers (a chicken raised specifically for meat) in York County, according to the census data.

There were a total number of 1,530 cattle, 44,243 hogs and 542,767 broilers in York County, according to the 2012 census data.

Calculated animal totals are even higher in neighboring Lancaster County, which had 10,556 cattle, 321,217 hogs and 4,070,755 broilers, according to the 2012 census data.

Lancaster had 5,657 farms, totaling 439,481 acres of land, according to the 2012 census.

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By comparison, Sunnyside Farm, a sustainable, family-owned farm of 12.75 acres in Newberry Township, has five cattle, 400 to 450 laying hens and about eight pigs each year.

Sunnyside's sustainable approach is not the norm, according to Kraft.

"There's a sense, I think for a lot of us, when we think of butchering meat we still picture either the neighborhood butcher ... or we might think of a slightly more industrialized version like where Rocky goes to work and punches slabs of beef," the professor said. "That's not the huge factories that Tyson is using for chicken."

More than 'cow farts': While methane, or the factor "people make fun of a lot" — cow flatulence, largely contributes to climate change, it is not the only impact factory farms have on the environment, Kraft said.

"If you think about a farm that you might have grazing animals on, the pigs and the chickens will go through and eat part of the grass," he said. "If you leave pigs out long enough, they'll eat it down to the ground."

On a factory farm, there is no room to roam, Kraft said.

A feedlot is just about a square foot of mud and feces, he said.

"There's no grass, no undergrowth that's capturing the carbon," he said.

The loss of carbon capturing is coupled with greenhouse gases produced by the animals.

Sustainable farms, such as Sunnyside at 1865 York Road, are able to maintain carbon capturing by limiting the number of animals per plot of land.

"We have the number of cattle and the number of laying hens that our property can support," said Dru Peters, who runs Sunnyside with her husband, Homer Walden, and her daughter Claire O’Brien. "And by support I mean my cattle can move around the farm 12 months out of the year."

The farm's laying hens are in mobile pens designed by her husband, Peters said.

Hens are moved around the farm to constantly have new grass to graze on, she added.

"That idea of having enough ground for the amount of animals that I have is exactly why my eggs cost more than other eggs, because I can keep them out on the field all year long," she said. "I'm not putting them inside in a building where they live in their fecal matter for any amount of time. I don't do it with my cows, I don't do it with my egg layers and I don't do it with my pigs."

Individual change: Despite the major impact animal agriculture has on climate change, it is one of the most direct changes that can be made on the individual level, Kraft said.

As his "vegan friends would say," one option is to stop eating animal products altogether, Kraft said.

A 2014 study done in the United Kingdom found that the average 2,000 calorie high-meat diet produced 2.5 times as many greenhouse gas emissions as the average 2,000 calorie vegan diet.

The study concluded that moving from a high-meat diet to a low-meat diet would reduce an individual's carbon footprint by 2,028 pounds of carbon dioxide per year, moving to a vegetarian diet would reduce the carbon footprint by 2,711 pounds of carbon dioxide per year, and moving to a vegan diet would reduce the carbon footprint by 3,439 pounds of carbon dioxide per year.

A vegan diet also can save water. Kraft said it takes 1,800 gallons of water to produce one pound of beef and just 100 gallons of water to yield the same pound in corn.

"We could, if we changed the way that we grow our food — and by growing food I’m meaning both vegetables and produce as well as meat — we could do it and still have a nutritious diet that could feed everybody," Kraft said.

Switching to a plant-based diet is not the only way consumers can make sustainable choices when it comes to food, he added.

"Even if you move to eating seasonally, locally pasture-raised meat, you’ve made a huge difference right there," Kraft said.

'Sustainable' meat: There are options for so-called sustainably sourced meat in York County, such as Sunnyside Farm.

The farm also grows produce and cut flowers, all grown without pesticides — even those that are certified organic, Peters said.

"Our farm is based on this idea that we sell directly, we grow it and we sell directly to consumers," she said. "In the larger context of farming, that is so unusual."

Peters said she believes her farming method yields better-tasting products.

"It's so easy to see the difference; you get a pound of hamburger from us and you can do a blind taste test, and it is not difficult to tell at all," Peters said.

Peters brings her products to farmers markets in Hershey and in Washington, D.C.

Those interested can reach out on the farm's website or with a Facebook message to pick up items.

However, just switching to purchasing sustainable meat won't make a difference on the overall market, Kraft said.

"It's not just changing what you're doing; you have to tell people why you're changing," he said. "So if you tell Giant and Weis that that's what you want, and if you stop buying the pre-packaged tube of ground beef from Sam's Club, they’ll stop carrying it."