Factory farming is to blame due to waste the high concentration of livestock in one area, and the amount of greenhouse gases their wasted, and farts produce. Plus the amount of water in a month long period it takes to keep a cow hydrated properly use more than 10x the amount a person uses. All I can say is watch this documentary called Cowspiracy that will really open your eyes.
Yes, factory farming does contribute but, also the burning of fossil fuels and deforestation. As the earth warms we have a cascading effect occurring. As ice sheets melt the excess fresh water desalinates the ocean and slows the global current circulation, which moderates global temperatures. As global currants slow, more severe and unpredictable weather occurs. With the melting of the permafrost in the arctic and sub arctic regions additional methane gas from rotting vegetation formally in a deep freeze is emitted into the atmosphere.