I would go one step further though and say that even an equal, per-capital emission standard on an annual basis is unfair for nations that are newly industrializing. Let's say hypothetically that next year, China starts creating the same per-capita emissions as the United States. It would be wrong to say then that China has caused an equal, per-capital level of climate damage and has to make an equal amount of reduction, when the decades of far-higher US emissions are much more responsible for the mess we find ourselves in.
Some versions of this idea, of focusing on cumulative emissions, are percolating through the policy arguments. Here's Jim Hansen talking about which countries have responsibility for initial reductions:
The moratorium must begin in the West, which is responsible for three-quarters of climate change (via 75% of the present atmospheric CO2 excess, above the pre-industrial level), despite large present CO2 emissions in developing countries.
I also heard Nicholas Stern say something similar in a radio program, that primary responsibility for addressing the problem belongs to the nations that have produced the majority of the excess carbon stock in the atmosphere.
A just approach would determine a global emission level that gradually brings greenhouse gases down to a non-dangerous level, and then have differential per-capital allocations - higher emissions for nations with little cumulative responsibility, and the reverse for others. The goal would be to have equal, cumulative, per-capita responsibility for the excess greenhouse gas stock by some date. I think the year 2100 would be appropriate.
Of course this is all dancing on the head of a pin until the US and the rest of the world to decide to get serious about climate change.