Imagine that all the cows on Earth gathered to form their own country. The newly created Republic of Cowtania would be the world's third-largest emitter of greenhouse gasses, just behind the United States and China.That's because cows fart and poop. A lot. And bovine waste is rich with planet-warming methane and nitrous oxide.

In an effort to curb global greenhouse gas emissions, scientists and engineers are hard at work developing low-carbon versions of meat, milk and cowhide. Just this week, Brooklyn startup Modern Meadow wrangled $40 million in financing to fabricate leather. No cattle required.

To produce a hide, the firm collects collagen protein from genetically engineered animal cells. Collagen fibers can be arranged into a strong, supple material of any shape.