I.IntroductionThree important and inter-related global issues of the 21st century are: (i) atmospheric concentration of CO2at 385 ppm in 2008 (+37.5% compared with the pre-industrial level of 280 ppm) and increasing at the rate of 2 ppm y−1(0.52% y−1) with the attendant impact on the current and projected global warming, (ii) world annual energy use of 500 EJ (Exajoule = 1018Joules, 1 Quad = 1015BTU = 1.05 EJ), increasing at the rate of 2.2% y−1and projected to be 537 EJ by 2010, 590 EJ by 2015, 637 EJ by 2020, 687 EJ by 2025 and 737 EJ by 2030,1and (iii) food—insecure population of about 1 billion and increasing because of an increase in price of energy and the related input (e.g., fertilizer, irrigation), decline in per capita arable land area (caused by conversion to urban/industrial uses and increasing susceptibility to soil degradation), and reduction in per capita availability of renewable fresh water resources for agricultural use. Increasing energy demand is a major cause of CO2emission. Fossil fuel combustion for energy production emits between 0.14 to 0.28 Mg C Mwh−1of energy.2Thus, fossil fuel combustion and other anthropogenic activities have strongly impacted the atmospheric enrichment of several greenhouse gases (GHGs) with the attendant impact on climate change. Relative emission of GHGs comprises 79.9% energy-related CO2, 9.5% CH4, 5.8% N2O, 3.0% non-energy CO2and 1.8% other gases (www.climatetechnology.gov). With regards to the energy budget of the Earth, however, radiative forcing or the global warming potential of different GHGs must also be considered. Therefore, mitigating the increase in atmospheric abundance of CO2necessitates identification of options which: (i) reduce emissions by using low-carbon or no-carbon fuel sources, (ii) enhance energy use efficiency by minimizing losses, and (iii) sequester atmospheric CO2into other reservoirs with secure storage and long residence time. With increasing reliance on fossil fuel as the dominant energy source for most of the 21st century, disposal of CO2by engineering, chemical and biological techniques is important to reducing the atmospheric loading and minimizing the risks of climate change. Total emission of C, with business as usual during the 21stcentury, is estimated at 950 to 2195 Pg compared to only 300 Pg emitted between 1850 and 2000.3The rate of annual emission by 2100 is estimated at 20 to 35 Pg C y−1compared with the 1990 baseline emission rate of only 5.5 Pg y−1.3It is thus imperative that the anthropogenic emissions of CO2be sequestered in other global pools for long-term and secure storage. This article collates and synthesizes research information, and describes technological options of C sequestration to off-set anthropogenic emissions due to fossil fuel combustion, land use change and other activities to stabilize the atmospheric concentration of CO2at a desired level (e.g., 550 ppm).