Something?
http://www.cquestrate.com/
The idea works like this:
* First, you heat limestone to a very high temperature, until it breaks down into lime and carbon dioxide.
* Then you put the lime into the sea, where it reacts with carbon dioxide dissolved in the seawater.
The important point is that when you put lime into seawater it absorbs almost twice as much carbon dioxide as is produced by the breaking down of the limestone in the first place.
This has the effect of reducing the amount of carbon dioxide in the atmosphere. It also helps to prevent ocean acidification, another problem caused by the increase in the amount of carbon dioxide in the atmosphere.
If done on a large enough scale it would be possible to reduce carbon dioxide levels back to what they were before the Industrial Revolution.