Also, don't become too pessimistic. Even here, its pretty obvious that people tend to fall into two camps: doomers or deniers. Very few in between. I have spent the better part of a year struggling with depression related to the realization of the scale of environmental and sustainability issues facing civilization. I was a doomer, and some days, I still am. That said, I also see that the uptake of renewable energy is accelerating. Electric car sales were considered negligible two years ago, and now they are growing fast. Thats not to say that there aren't HUGE challenges facing us. But I also feel more hopeful that things will eventually change in time.
Decrease your transportation needs. Running a gasoline vehicle for 1 second produces more CO2 than turning off all of the zombie loads in your house. Move closer to work so your commute is shorter and you'll cut your carbon footprint more than any other thing you could do.
I guess we can pick the alternative energy source of our liking and evangelize for it. We can also technologically, monetarily, electorally and emotionally support the people who are looking for and deploying these alternatives. At least temporarily switch to ecologically cheaper foods, so that species who are facing problems get a few decades of rest, and recommend your preference to others who might enjoy the change as well.
As somebody else mentioned elsewhere in the thread, get involved with 350.org, or alternatively Greenpeace. AFAIK, these are the largest and most effective organisations in the climate change area.
We're well past the point where changing individual behaviour will be enough (and also, this strategy has been promoted over the last 30 years and largely failed - emissions are still rising). We need protests and actions that will lead to policy changes around the world and the shutdown of the fossil fuel industry.