There are various schemes offering carbon offsets. What attributes would make such a scheme meaningful? That is, where would my additional money into the scheme lead to lower global emissions than without it?
Based on the question as currently worded, I believe you're concerned about fraudulent and 'anyway' offsets - paying money for a business to do what they would have done anyway. For example, if a company knew it was going to install solar panels on a roof that they were already going to install solar on because of tax incentives, you wouldn't want to give them money for what was already economic for them.
Here are a few characteristics of carbon offsets that you may want to purchase:
- you are paying into a new low carbon energy infrastructure, as opposed to existing infrastructure.
- you are purchasing from a well regulated electricity market where claims can be verified. Try to avoid schemes in distant, unregulated countries, unless you have good reason that there is truth in the carbon offset claims.
- the offsets you are purchasing are not redundant to government incentives or pre-existing market benefits (eg don't pay for a company to go from incandescent to cfl - they should already be doing it because it will save them money).
- you are driving a new technology to market and scale. Your dollars are best placed in technologies that not only offset the carbon you paid for, but promise to do more in the future. For instance if there is a new wind turbine blade that is already cost competitive with others on the market, but will likely drop further in cost as they are more widely adopted, support it!
The Economist did a great debate piece on this. Check it out.