One of the things that people point to is the idea of "off-setting" their carbon footprint. They pay for people to do things like plant trees or other things so that they feel that someone is taking enough carbon out of the atmosphere to off set the amount that they are putting in.
This is also a part of the carbon trading system where certain companies pay to offset their emissions. The problem is that there are huge amounts of faults in the system and there is also no real way of holding people accountable if they just take your money and don't plant trees, etc.
So I would say right now there are few things that one can do if they are in a situation where they absolutely cannot be sustainable. But Carbon Offsets are one possible option.