This has puzzled me for years:
The general public has a major lack of understanding of how eating meat and dairy contributes to climate change, according to a survey of Europe, the Americas, Asia, and Africa by the market research organization Ipsos MORI. Although meat and dairy production accounts for roughly 15 percent of total global carbon emissions — equal to exhaust emissions from the international transportation sector — less than 30 percent of survey respondents identified meat and dairy production as a major contributor to climate change. More than twice as many — 64 percent — said transportation was a major contributor.
Interestingly, many people are aware that deforestation contributes to global warming, but don’t apparently don’t connect deforestation to clearing land to run livestock.
I guess the meat and dairy industry has a better PR team than the oil and gas companies.
The Earthist Chronicles 
The correlation is not that simple, direct or accurate. In cultures that have traditionally existed on a a meat-based diet, population growth (fertility rates) remained low. The single biggest factor pushing the human impact on warming is overpopulation. Nothing else is even close, and it has been the switch to agricultural and a diet heavier in vegetable consumption that has fostered this population explosion.
If we don’t get a handle on overpopulation, it doesn’t matter what we eat. We will continue draining and polluting aquifers, felling forests, draining swamps, wiping out habitat and reducing biodiversity. Overpopulation is the root. All else is hacking at the leaves and branches.