In the past 150 years, such activities have pumped enough carbon dioxide into the atmosphere to raise its levels higher than they have been for hundreds of thousands of years. (pearltrees.com)
Too little will not produce enough carbon dioxide for the bread to rise as well as it could. (imglutenfree.com)
It has never been tried at a large scale, and nobody knows if it can be used worldwide to remove enough carbon dioxide to slow warming. (seeker.com)