CO2 MITIGATION BY AGRICULTURE - AN OVERVIEW

Agriculture currently contributes significantly to the increase of CO2 in the atmosphere, primarily through the conversion of native ecosyst ems to agricultural uses in the tropics. Yet there are major opportuni ties for mitigation of CO2 and other greenhouse gas emissions through changes in the use and management of agricultural lands. Agricultural mitigation options can be broadly divided into two categories: (I) str ategies to maintain and increase stocks of organic C in soils (and bio mass), and (ii) reductions in fossil C consumption, including reduced emissions by the agricultural sector itself and through agricultural p roduction of biofuels to substitute for fossil fuels. Reducing the con version of new land to agriculture in the tropics could substantially reduce CO2 emissions, but this option faces several difficult issues i ncluding population increase, land tenure and other socio-political fa ctors in developing countries. The most significant opportunities for reducing tropical land conversions are in the humid tropics and in tro pical wetlands. An important linkage is to improve the productivity an d sustainability of existing agricultural lands in these regions. Glob ally, we estimate potential agricultural CO2 mitigation through soil C sequestration to be 0.4-0.9 Pg C y(-1), through better management of existing agricultural soils, restoration of degraded lands, permanent ''set-asides'' of surplus agricultural lands in temperate developed co untries and restoration of 10-20% of former wetlands now being used fo r agriculture. However, soils have a finite capacity to store addition al C and therefore any increases in C stocks following changes in mana gement would be largely realized within 50-100 years. Mitigation poten tial through reducing direct agricultural emissions is modest, 0.01-0. 05 Pg C y(-1). However, the potential to offset fossil C consumption t hrough the use of biofuels produced by agriculture is substantial, 0.5 -1.6 Pg C y(-1), mainly through the production of dedicated biofuel cr ops with a smaller contribution (0.2-0.3 Pg C y(-1)) from crop residue s. Many agricultural mitigation options represent ''win-win'' situatio ns, in that there an important side benefits, in addition to CO2 mitig ation, that could be achieved, e.g. improved soil fertility with highe r soil organic matter, protection of lands poorly suited for permanent agriculture, cost saving for fossil fuel inputs and diversification o f agricultural production (e.g. biofuels). However, the needs for glob al food production and farmer/societal acceptability suggest that miti gation technologies should conform to: (I) the enhancement of agricult ural production levels in parts of the world where food production and population demand are in delicate balance and (ii) the accrual of add itional benefits to the farmer (e.g., reduced labor, reduced or more e fficient use of inputs) and society at large.