No legitimate authority on climate change said that animal ag is the leading cause . You're misquoting a UN report that theorized it was one of the top 3 causes...

this peer reviewed world bank funded report puts the percentage of greenhouse gasses contributed by animal agriculture at 51%. So right there your statement is wrong. A legitimate authority does say animal ag is the leading cause. But obviously there's some disagreement, so let's examine that.

The older estimate funded by the UN that you refer to was 18%, (which even in that report put it as the second leading cause and significantly ahead of transportation) but This article does a good job of explaining the differences between the two studies, and why the World Bank funded study is actually more reliable. For your convenience, here is a a listed summary I put together of the points in that article.

• The FAO authors are not environmental assessment experts while the World Bank authors are.
• The FAO grossly underestimated the livestock population by more than half. They used a number of around 21 billion when the real number is around 50 billion. The FAO themselves have since acknowledged this.
• The FAO did not include CO2 do to livestock respiration in it's calculations, despite this being a requirement under the Kyoto protocol:

Livestock [like automobiles] are a human invention and convenience, not part of pre-human times, and a molecule of CO2 exhaled by livestock is no more natural than one from an auto tailpipe

• The FAO underrepresents the Global Warming Potential (GWP) of methane by by 2/3 by calculating it's effects over a 100 year period instead of the 20 year period that is agreed upon by climate scientists.

ton for ton methane contributes to global warming 23 times more than C02 when viewed over a 100-year timeframe, and 72 times more over a 20-year timeframe

• The 20 year time frame is also much more important when we look at potential feedback loop systems. The reality, which is that methane takes it's affect intensely over a short period rather than slowly over a long period, means that there is a greater chance of methane triggering certain environmental feedback loop situations that would exponentially worsen the warming we experience.
• Methane's short lifespan does offer us our greatest opportunity for preventing catastrophic climate change. Because it stays in the atmosphere for only 12 years, drastically reducing emissions by severely cutting back on livestock offers the chance to see a relatively rapid reversal of the current warming trend.

Additionally, whereas most industries can only achieve significant GHG emission reductions through a switch to renewable energy (which will necessitate some 20 years and $18 trillion dollars for the development of sufficient infrastructure), the livestock industry is unique in that most of its emissions do not come from energy use but from biological processes.[27]

Thus, while enormous obstacles stand in the way of widespread implementation of renewable energies, significant reductions in livestock populations on the other hand can be accomplished with relative ease (made all the easier by forthcoming meat replacement technologies). And, with the industry as the world’s leading methane and total GHG emitter, reductions here would have a greater (and, importantly, quicker) positive environmental impact.

While governments continue to struggle to agree on measures that would increase renewable energy infrastructure significantly, alternatives to livestock products could be scaled up quickly to reduce today’s grave risk of climate change significantly.

One other bit of yours that I would like to address.

It's also well known that veganism is more based off emotion than logic.

Funny, because a statement like this is neither scientific nor logical. It's a perception. And depending on the vegan in question it may be an accurate perception, but you can not make such a broad statement about veganism. It is not "well known", it is "commonly perceived". However, I for one take an almost purely logical view on veganism. I am not an emotional person. I am vegan because I think the logic and ethics behind veganism is far superior to the logic behind carnism. Vegan ethics follow a very simple logical pattern that sees consistent application to all circumstances; that is to say vegan ethics are never confronted by a situation in which they must be contradicted. Carnist ethics however are often confronted by situations in which they must be contradicted. Veganism is by far the more logical system of ethics.