Two women on London's 29 November climate march carry home made placards with the message that animal agriculture is the leading cause of global warming with the implication that going vegan is probably the biggest contribution anyone can make to limiting and hopefully eventually reversing global warming and climate change.

The climate change march in London was held as part of a series of rallies worldwide prior to the COP21 Paris climate change talks. Activists want decisive action to limit the rise in average global temperature to 2 degrees celcius above pre-industrial levels.

Recent studies have suggested that livestock agriculture, even more than fossil fuels, is the greatest contributor to global warming.

Worldwide there are approximately 1.5 billion cows and a cow releases between 70 and 120 kg of Methane per year and scientists estimate that methane has a warming effect on the climate 23 times greater than CO2.

Not only does livestock farming use approximately one third of the usable agricultural land but another third is taken up for crop production to feed the livestock and both are major causes of deforestation which acts to further accelerate global warming.