Sandbag is about stopping emissions from occuring in the first place but once they're out there is there anything that can be done to get them back?

Obviously trees and other forms of biomass absord carbon dioxide and store it in their structures - but it's a form of temporary storage, since plants and trees eventually decay or are burnt, re-emitting the carbon dioxide. Saturday's Guardian featured an article about a new technology for scrubbing emissions out of the air - scientists at Columbia University in New York have developed a prototype machine capable of capturing a tonne of CO2 a day - costing only £100,000 to build and small enough to fit in a shipping container.

The breakthrough is a reduction in the energy required to release the captured gas and recycle the absorbent. The world emits roughly 100 million tonnes of carbon dioxide a day so that's a lot of machines to make an impact and the effectiveness of the whole venture also depends on what happens to the stored gas next. Locked in a solid compound or in an underground storage facility it does represent a genuine reduction in atmospheric concentrations - used to speed up growth rates of biofuels and it's simply another temporary solution since the burning of the biofuel releases it back again.

Maybe a less technological answer is to consider how the free capture facility provided by mother nature can help. Using wood in long-life buildings and furniture or even burying trees/biomass would achieve the same effect (this is after all how fossil fuels were created) - capturing and storing the CO2 emitted from biomass energy when it is burnt would also help reduce net concentrations in the atmosphere.  Photosynthesis is relatively inefficient at converting the suns energy so speeding that up would help. I also like my friend Si's idea of burying coal places where nobody can find it again. Ultimately all these ideas and many others (perhaps not Si's) are going to be needed - and the most exciting thing is that people all over the world are now applying themselves to the problem. Motivated no doubt by the belief that the winning solutions will be well rewarded when society starts to properly value negative emissions. Cleaning up emissions trading schemes is an excellent way to speed this along.