Date: Mon, 17 Sep 2001 16:32:03 -0400 To: scw@io.harvard.edu From: Steve Pacala Subject: sequestration text Dear Steve: The following is a first pass. Feedback please. Best, Steve Pacala Carbon sequestration is increasingly viewed as a possible solution to the carbon and climate problem. Conservation and renewable energy are essential, but insufficient by themselves. Nuclear power carries environmental and other risks, and fusion is many decades away. In contrast, technology already exists to capture CO2 from fossil fuel at relatively low cost (especially before combustion), and to sequester it in underground storage reservoirs (ref). Initial surveys of appropriate geological formations suggest the possibility of sufficient capacity to sequester a century's worth of fossil CO2 (on the order of one hundred billion tons of fossil carbon in depleted fossil fuel reservoirs and a thousand billion tons in deep saline aquifers, ref). Biological storage could also play an important role, but the total capacity of the biosphere is likely to be an order of magnitude too small (i.e. less than one hundred billion tons). To solve the carbon problem, sequestration must be highly effective. Reservoirs that leak even one percent per year into the atmosphere would produce annual emissions of ten billion tons of carbon from a stored pool of a thousand billion tons more than current global emissions from fossil fuel. Acceptably low emissions will require leakage rates beneath a tenth of a percent per year. Industrial investment in sequestration R&D is currently hampered by concerns about the public backlash that would follow a realization that we do not yet have the technology to monitor and manage sequestration sites. Deep saline aquifers typically cover hundreds of thousands of square kilometers and might contain unmapped faults allowing rapid escape. One prime site for sequestration (the Alberta Basin) contains an estimated 300,000 exploration wells, any one of which could develop a leak (ref). The atmospheric sampling program in the proposed carbon observing system will provide the fundamental science and technology necessary to detect, measure, track and locate leaks of stored CO2. A national network to monitor and regulate sequestration would almost certainly look like the proposed network a grid of stationary towers for coarse resolution, together with aircraft sampling and real-time model inversion to track-down specific leaks. Some such leaks could be repaired (i.e. those from a failed concrete seal of an old well); others might require a cessation of sequestration at the site. The public will view sequestered CO2 as an unacceptable legacy for future generations unless measurements show it to be safe and a credible plan is in place to manage it. The existence of technology to monitor carbon sequestration will remove a primary source of uncertainty that currently inhibits investment by the private sector in sequestration R&D.