Addressing the Grand Challenge of atmospheric carbon dioxide: geologic sequestration vs. biological recycling

On February 15, 2008, the National Academy of Engineering unveiled their list of 14 Grand Challenges for Engineering. Building off of tremendous advancements in the past century, these challenges were selected for their role in assuring a sustainable existence for the rapidly increasing global community. It is no accident that the first five Challenges on the list involve the development of sustainable energy sources and management of environmental resources. While the focus of this review is to address the single Grand Challenge of "develop carbon sequestration methods", is will soon be clear that several other Challenges are intrinsically tied to it through the principles of sustainability. How does the realm of biological engineering play a role in addressing these Grand Challenges?