Isn't NOT doing something even less efficent?

Here is a way to capture CO2 that will pay for itself. A- Grow trees B-cut and mill trees into lumber C- Sell the lumber to pay for the process. D-see A.

This long discussed 'quick fix' method of geoengineering ...

How quick? The prospect of manipulating the world's environment makes me nervous.

It would be reasonable to spend some time studying this, and then performing smaller scale tests and waiting several years to be assured there are no unforeseen side effects. Then, only after passing some sort of critical review, the actual implementation.

In theory you could grow biomass and then dump it in an anoxic sea, such as the bottom of the Black Sea. This way the carbon would stay fixed and not re-enter the biosphere for a long time.
An easier way to sequester carbon is to remove the CO2 from gas at the source as the gas is pumped out. Then force the CO2 down into exhausted gas deposits.

I love the idea, but they're right, it IS inefficient. Also a biological impact study should be done to assess the possible drawbacks of mass producing diatoms to the detriment of other plankton. Food webs can be impacted severely here.
On the plus side it would solve our unemployment related problems.