The hamburgers and cheese that come from U.S. cattle may be favorite fare at many summer cookouts, but the methane the same cows produce is significantly less appetizing.

That's especially the case for sustainable investors looking for a low-emission place to park their cash. "Enteric fermentation," or livestock's digestive process, accounts for 22 percent of all U.S. methane emissions, and the manure they produce makes up 8 percent more, according to the U.S. Environmental Protection Agency.

And although agriculture is a growing industry as the world looks to feed its swelling population, some investors are reluctant to support a sector with such a hefty methane footprint.

"There are a lot of factors or buckets that go into agricultural emissions, but livestock tends to be one of the largest focuses," said David Nicola, portfolio manager of the Gratitude Railroad Farmland Fund, which launched this week and is targeting $40 million in capital commitments focused on regenerative agriculture.