"Offsets are an imaginary commodity created by deducting what you hope happens from what you guess would have happened"

Green reasons to oppose Australia’s carbon price | Green Left Weekly

Carbon offsets are the way the government says Australia will reach its 5% emissions cut target. They are, to put it politely, a gigantic scam.
When you buy a carbon offset, what exactly are you buying? No one can tell you for sure.
Carbon market researcher Larry Lohmann said in a 2008 article, carbon offsets assume “knowledge we don't have”.
He said: “All these ‘carbon offsets’ are supposed to be climatically equivalent to cutting your coal, oil or gas use.
“But you can’t prove that. You can add up how much greenhouse gas your offset ‘saves’ only if you assume that without it, only a single world would be possible. This assumption has no scientific basis.
“Researcher Dan Welch sums up the difficulty: ‘Offsets are an imaginary commodity created by deducting what you hope happens from what you guess would have happened.’”