Just in the context of Hansen’s points st, I wanted to recommend the following post from Celsias last week, particularly the two points I will paste here.
http://www.celsias.com/ 2008/ 01/ 14/ hot-air-and-snake-oil-carbon-offset-upsets/

Regardless of one’s overall opinions on offsets, I think that there is great clarity in Kevin Smith’s points 2 and 5. Although I have long “known” these points, there is something in the way he articulates them… and adds urgency to Hansen’s points about not letting the carbon system enter the “active” pool in the first place…

“2) Carbon is permanently locked up in the ‘inactive’ carbon pool in the form of fossil fuels until it is extracted and burnt, and then it is released into the ‘active carbon pool’, a complex and incessant interchange between the oceans, forests and atmosphere. The only, incontrovertible way of dealing with climate change is to severely limit the flow of carbon from the inactive pool into the active cycle. This flow is a one-way process, and no matter how many offset projects are carried out, you can not reverse the damage that is done when carbon is released from one cycle to the other. It cannot be ‘neutralised’…

“5) Finally, there is the time lag issue. In fact there are two: First, when carbon is released into the atmosphere, it is part of the problem in terms of climate change, but the various carbon offset schemes are operating to supposedly neutralize these emissions over a much longer period of time, sometimes, as in the case of forestry offsets, over a period of a hundred years or more. If an individual or company keeps offsetting regularly, their rate of emissions increases rises at a much faster rate than the rate at which their activities are being ‘neutralised’ to the point at which, far from being ‘carbon neutral’, quite the opposite is true. The carbon in the atmosphere increases at a far greater rate than it’s supposed ‘neutralisation’…”

(Me again… The one very minor quibble I have with Smith’s point is that if one of the schemes to efficiently remove GHG’s from ambient air (and then effectively sequester them) were to ever come to fruition, then we could conceivably ‘neutralize’ the original (and historical) emissions from fossil fuels. The outlook for such schemes on a meaningful scale and on the required timeline is poor, as I understand it. Furthermore, on geologic timescales, carbon can be removed from the active cycle - that’s how the fossil fuels came about, obviously! But for current purposes, Smith’s point clearly stands… )

What needs to be added when talking about not building coal plants is what is to replace them, whether energy efficiency or some other peak power plants. Not building a plant is fine, but everybody sees the big hole left after you discuss it.