Terrestrial biomass is a huge short-term carbon reservoir (~2000 Gt C) that uses photosynthesis and plant respiration to exchange carbon with the atmosphere. This exchange sequesters 1.9 Gt C/a in terrestrial biomass, an amount that is almost counterbalanced by emission of 1.7 Gt C/a from deforestation, thus yielding a small positive sequestration gain of 0.2 Gt C/a. Considerable controversy exists on the exact carbon flux values, which is being addressed by research such as the FLUXNET-CANADA network. Because terrestrial biomass is a short-term storage solution for carbon, only increases in biomass can lead to increased carbon sequestration. Terrestrial biomass sequestration has some additional virtues such as revegetation of abandoned lands or protection of swamps, thus improving biodiversity and the environment. Earth scientists have shown, however, that SO₂ pollution slows biomass growth thus reducing its capacity to capture carbon (Savard et al., 2002). We can also determine past storage of biomass carbon in the geological record: could what it tells us impact carbon sequestration policies? We have to be part of this debate, because Earth Science matters!

The ocean is also a vast reservoir of CO₂. The concentration of dissolved CO₂ in the upper part of the ocean has increased over time, remaining in equilibrium with atmospheric CO₂ concentration, and therefore absorbinga vast quantity (1.9 Gt C/a) of anthropogenic carbon emissions. One scheme to sequester CO₂ tests fertilizing the photic zone, causing an algal bloom. Phytoplankton may then be consumed by other organisms, or settle to the bottom of the ocean, thereby sequestering carbon away from the atmosphere. One such experiment using iron sulphate fertilizer yielded troubling results such as release of isoprene, another GHG (Dalton, 2002). Unlike surficial oceanic water, the deep oceanis not in equilibrium with atmospheric CO₂ and could store huge amounts of anthropogenic carbon for hundreds of years. Sequestration involves either dissolving gas bubbles into seawater, or direct injection of liquid CO₂ to the seafloor, where solid clathrates are stable at the ambient pressure and temperature conditions. One major impact of CO₂ injection is a decrease in the pH of water near the injection site. New alternatives are being developed, including dissolution of CO₂ in a calcium bicarbonate solution, akin to limestone weathering, and then pumping this solution in the ocean to dilute it (Rau et al., 2003). There are many objections to CO₂ storage in the ocean, which will need to be addressed to make it acceptable to society. Earth scientists need to take a leadership role in assessing the long-term stability and environmental impact of ocean sequestration. We also have unique and vital geochemical expertise, which can help us understand and forecast the role of the oceans in past and future carbon absorption.

Geological storage involves sequestering CO₂ in rocks. The most advanced concept and one that has commercial application in terms of oil and gas fields is to inject CO₂ into geological reservoirs for enhanced oil recovery (EOR) or storage of dry acid gas. In fact, Canada hosts the International Energy Agency EOR test site at Weyburn, Saskatchewan. Injection of CO₂ into geological reservoirs is quite similar to the natural gas distribution network that relies on natural, engineered reservoirs to stock gas for peak consumption periods. Another alternative is to adsorb CO₂ onto organic matter in deep coal beds unsuitable for mining. By this process, CH4 is displaced by injected CO₂ thus producing natural gas. Obviously, EOR and CH4 production from coal beds have economic value, but the positive impact on Canada's CO₂ emissions is reduced by the amount of oil and gas eventually produced and combusted. The CO₂ can also be injected and dissolved into a confined aquifer, a method used by Norway's Statoil in the Sleipner gas field to avoid emission of CO₂ into the atmosphere as a byproduct of natural gas production. Finally, CO₂ can be sequestered as carbonate minerals. For example, olivine or serpentine react naturally with CO₂ to form magnesite (MgCO3). There are more than enough magnesium silicate rocks in ophiolite belts and in asbestos mine waste in Canada to store Canada's CO₂ emissions for centuries. A collateral and environmentally friendly effect of the use of mineral carbonation is the recovery of mining waste in asbestos production districts such as the Eastern Townships in Quebec and the Cassiar district in British Columbia. The most significant advantage of mineral carbonation by magnesite is that it is the only permanent form of carbon sequestration. Mineral carbonation is thermodynamically favoured, but the rates of reaction present a challenge when one considers sequestering the CO₂ emissions from an average power plant. In addition, magnesite manufactured from carbon sequestration processes could become a magnesium ore: magnesium metal production from magnesite releases CO₂ but increased use of magnesium in vehicles would help reduce GHG emissions. Geological storage represents the most advanced of the alternatives for CO₂ sequestration, and has a track record of industrial implementation and review by international panels in instrumented test sites. It is also the only long term to permanent form of CO₂ sequestration. Earth Sciences clearly matters!