Managing Terrestrial Carbon in a Changing Climate

Abstract

The threat of abrupt climate change by increase in atmospheric concentration of CO₂ and other greenhouse gases has enhanced the interest and urgency of identifying strategies for reducing and sequestering anthropogenic emissions. The latter are caused by land use conversion that began with the dawn of settled agriculture several millennia ago, and by fossil fuel combustion that began with the onset of the industrial revolution in about 1750. Emissions from land use conversion during the pre-industrial era until about 1850 are estimated at ~320 Pg. Since 1850, emissions from fossil fuel combustion are estimated at ~350 Pg and those from land use conversion at ~150 Pg. These and other anthropogenic activities have caused drastic perturbation of the global carbon cycle with increase in the atmospheric C pool and an attendant decrease in the pedologic, biotic, and geologic (fossil fuel) pools. Together, the pedologic pool (4,000 Pg to 3 m depth) and the biotic pool (620 Pg), called the terrestrial pool, is the third largest pool, after the oceanic (38,000 Pg) and the geologic (~5,000 Pg). The depletion of the terrestrial C pool has created a C sink capacity which can be filled by conversion to a restorative land use and adoption of recommended soil, plant, and animal management practices. The process of transfer of atmospheric CO₂ into the pedologic and biotic pools is called carbon sequestration. This natural process contrasts with that of the geoengineering techniques of carbon capture and storage (CCS) involving geologic and oceanic storage and mineral carbonation of CO₂ into calcite etc. The strategy of biosequestration, in addition to being cost-effective, has numerous ancillary benefits. It is a truly win–win option. Specifically, it improves soil quality, enhances agronomic productivity, and advances food security. Improvement in soil quality by C sequestration is related to generation and stabilization of micro-aggregates created through formation of organo-mineral complexes. The strategies of biosequestration involve development of a positive ecosystems C budget in soil by mulch farming, conservation agriculture, no-till systems, integrated nutrient management including biological N fixation and mycorrhizae use of amendments including biochar, and adoption of complex farming systems such as agroforestry. There is no silver bullet or panacea, and the choice of a practice/strategy depends on site-specific conditions.