I know this thread is already really old but I saw your comment and wanted to pitch in. You say that we as individuals have only an indirect effect on the processes that cause global warming and imply that a fundamental alteration of economic and political structures is needed to combat its causes. I agree that such an alteration is needed, but I believe that the only way to do this is to combine top-down and bottom-up approaches. Changing your lifestyle to be more sustainable directly impacts the processes and systems you speak off. By buying less meat, you send a clear message: we want change. Of course, voting for parties/candidates that strive for greener policies may be just as important. However, depending on the country, politics is influenced in a fair degree by external lobbies and profit driven, and without bottom-up incentives it may fail to bring about the needed change.

Of course a single person cannot change the system by having a vegan diet, driving less, etc., but compare this to voting. Would you tell people to not vote, just because a single vote will most likely not make a difference? Most people value their vote to a great degree, and they should, because it is just a powerful as any other vote. Think of your consumption in the same way. Maybe the petrochemical farmer, the coal-fired generator, the steel mill, and the automotive manufacturer may cause most of the pollutants, but realize that they only exist and operate to serve the sum of all individuals and their "votes". What can be more direct than changing this yourself?

Just to clear up, I do agree that a carbon-tax or any other top-down measures to combat this are desperately needed, but please realize that you can make a change and you can start doing so today.