I don't think I have to belabor this point, but eating factory farmed hamburgers and steaks has a much larger ecological impact than lentil soup or a nice veggie stir-fry. Here's a Scientific American article that provides some concrete statistics. A half pound of conventional veggies shipped all the way from Peru? 4.4 ounces of co2 equivalent.
A half pound of hamburger? The equivalent of 3.6 to 6.8 POUNDS not ounces of co2 equivalent. (It's actually a small amount of methane but that has 23 times the climate changing potential of co2.)
So, point is: eat very little meat, and what you eat should be raised naturally, and ideally low on the food chain, like chicken not beef. But an occasional grass-fed hamburger on very special occasions can be ok--as long as special occasions don't include all days that end with the number 3, every Sunday, or days that start with T or S. More like: 3 or 4 birthdays and a few holidays--leading to meat and fish consumption on the order of two pounds a month. (Or just make Sunday your meat night and have one big 1/2 pound of meat then.) The Earth could sustain that level of meat consumption. In fact, it would welcome it: right now we eat about 435 million tons of meat and fish each year (275 and 160 million tons respectively). If everyone pulled back to a kilo (or 2.2 pounds) per month we'd only be eating 41 million tons per year--just 9% of current meat and fish levels. Even at a population of 9 billion, this number would only rise to 54 million or 12% of current consumption levels.
Along with being healthier, our oceans would heal, greenhouse gas emissions would fall, we could go back to raising animals more naturally, and grow more vegetable and grain crops for human consumption leading to less hunger (if better distributed, which would mean that total farming jobs wouldn't have to fall). I know, it's a dream, but cut your own meat consumption--that's a starting point and then encourage others to follow suit. And I've found that it's definitely easier to encourage people to make meat a smaller part of their diet than abstain altogether. Good luck!