Accelerating the Transition to 0 Greenhouse Gas Emissions by Reducing Methane Emissions from Cows. Volta Greentech is on a mission to battle global warming – by reducing methane emissions from cows. Did you know that there are 1.5 billion cows on the planet that together burp out 5% of the world’s greenhouse gas emissions? The startup tells us that that’s 2x more emissions than the world’s fleet of airplanes.