This article makes sense, but the study you cite does not point to what you are pulling from it. Yes, beef is worse technically than chicken meat in terms of greenhouse gas emissions, but a global move towards chicken would be disastrous.

The biggest finding from the study is that consumers have the power to shift the food system in a way that the best practices in animal agriculture just cannot. According to the study:

"Today, and probably into the future, dietary

change can deliver environmental benefits on

a scale not achievable by producers. Moving from

current diets to a diet that excludes animal products has transformative potential, reducing food’s land use by 3.1 (2.8 to 3.3) billion ha (a 76% reduction), including a 19% reduction in arable land; food’s GHG emissions by 6.6 (5.5 to 7.4) billion metric tons of CO2eq (a 49% reduction); acidification by 50% (45 to 54%); eutrophication by 49% (37 to 56%); and scarcity-weighted freshwater withdrawals by 19% (−5 to 32%) for a 2010 reference year"

It is a no brainer that a vegan diet is abosolutely the best thing you can do for the environment. :)