According to a 2015 Chatham House Report “Changing climate, changing diets”, people in industrialized countries consume on average around twice as much meat as experts deem healthy. In the US the multiple is nearly three times. Adoption of a healthy diet would therefore generate over a quarter of the emission reductions needed by 2050!
I haven't looked into this aspect of climate change, so I searched some info on methane gas and found this.
Methane's lifetime in the atmosphere is much shorter than carbon dioxide (CO2), but CH4 is more efficient at trapping radiation than CO2. Pound for pound, the comparative impact of CH4 on climate change is more than 25 times greater than CO2 over a 100-year period.
This leads me to Causes of Climate Change, which has a nice slide show that talks about climate forcing and talks about natural forcings, human-induced forcings and their net change on earth.
So us carnivores can reduce our meat consumption to have a positive effect on the environment.
I live in California, where there's been years of drought, when asked to ration water, many people did and it had a positive effect. People let their lawns dry up, bought tanks to store reclaimed water for their yards, etc.. So, reducing meat consumption seems like it could be a realistic campaign where we can play a part in reducing global warming.