This is one of the questions people use to ask when you explain Supercritical Fluid process and you argue that is a green process, or you talk about sustainable development.
Of course CO2 is regarded as one of the most important environmental problems and its relation with climate change and global warming seams well establish.
However, although most Supercritical Fluids processes employ CO2 as solvent, we don't have to forget that the process DOES NOT PRODUCE CO2 and, moreover, most of the CO2 employed is recirculated.
Related with CO2 problem, today I’ve found a new about one more possible solution.
Craig Venter at TED2008 (Technology, Entertainment and Design) talked about his latest research into "fourth-generation fuels", biologically created fuels with CO2 as their feedstock.
The idea is to create genetically new bacterias that will produce methane form atmospheric CO2.
It seems more plausible than transforming CO2 in fuel using nuclear energy.
But, having to play with DNA, the idea will have lots of detractors, perhaps more than nuclear energy.