![]() ![]() Concentrations of methane (CH 4) and nitrous oxide (N 2O) have also increased steadily over the same period (IPCC 2001, 2007 Prather et al. The concentration of carbon dioxide (CO 2) has increased by 31% from 280 ppmv in 1850 to 380 ppmv in 2005, and is presently increasing at 1.7 ppmv yr −1 or 0.46% yr −1 ( WMO 2006 IPCC 2007). Consequently, the concentration of atmospheric GHGs and their radiative forcing have progressively increased with increase in human population, but especially so since the onset of industrial revolution around 1850. These and other observed climate changes are reportedly caused by emission of greenhouse gases (GHGs) through anthropogenic activities including land-use change, deforestation, biomass burning, draining of wetlands, soil cultivation and fossil fuel combustion. In addition to the sea-level rise of 15–23 cm during the twentieth century ( IPCC 2007), there have been notable shifts in ecosystems ( Greene & Pershing 2007) and frequency and intensity of occurrence of wild fires ( Running 2006 Westerling et al. The rate of increase in global temperature has been 0.15☌ per decade since 1975. Earth's mean temperature is projected to increase by 1.5–5.8☌ during the twenty-first century ( IPCC 2001). Global surface temperatures have increased by 0.8☌ since the late nineteenth century, and 11 out of the 12 warmest years on record have occurred since 1995 ( IPCC 2007). Biotic and abiotic C sequestration options have specific nitches, are complementary, and have potential to mitigate the climate change risks. In comparison, biotic techniques are natural and cost-effective processes, have numerous ancillary benefits, are immediately applicable but have finite sink capacity. ![]() These techniques have a large potential of thousands of Pg, are expensive, have leakage risks and may be available for routine use by 2025 and beyond. Engineering techniques of CO 2 injection in deep ocean, geological strata, old coal mines and oil wells, and saline aquifers along with mineral carbonation of CO 2 constitute abiotic techniques. Carbon sequestration implies transfer of atmospheric CO 2 into other long-lived global pools including oceanic, pedologic, biotic and geological strata to reduce the net rate of increase in atmospheric CO 2. Of the three options of reducing the global energy use, developing low or no-carbon fuel and sequestering emissions, this manuscript describes processes for carbon (CO 2) sequestration and discusses abiotic and biotic technologies. Developing technologies to reduce the rate of increase of atmospheric concentration of carbon dioxide (CO 2) from annual emissions of 8.6 Pg C yr –1 from energy, process industry, land-use conversion and soil cultivation is an important issue of the twenty-first century. ![]()
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