Reduce Greenhouse Gas Emissions
According to figures from the Charles Darwin University in Australia, "About one-quarter of the total methane emissions caused by human activities comes from domesticated animals." Those animals at the top of the list include: cattle, dairy cows, buffalo, goats, sheep, camels, pigs, and horses.

Most of the methane is produced during digestion and so can not be recaptured. However, 25% to 33% of it can be reclaimed by proper disposal of the animals manure, which is unfortunately not a common practice in 1st world agriculture.

For those of you who don't know, since the beginning of the Industrial Revolution, atmospheric methane concentration has more than doubled, and has contributed 20% to the enhancement of the greenhouse effect, second only to carbon dioxide. While it is a "natural" gas and non toxic, it is most certainly not good for our environment on any level.

If you want to help make a serious impact in reducing the amount of greenhouse gases produced by human activity, you can start by reducing or eliminating the above animals from your diet, including dairy from said animals.