http://www.thestarphoenix.com/touch/story.html?id=10331200
Soft geoengineering could mitigate change BY PAUL HANLEY, THE STARPHOENIX OCTOBER 28, 2014 Climate change looms over our children's future. For those not confident in global targets to reduce C02 emissions, geoengineering - the deliberate large-scale intervention in the Earth's natural systems to counteract climate change - offers a last-ditch solution.Proposals have been made to fertilize or increase the alkalinity of the oceans in order to increase carbon absorption or to release stratospheric aerosols to block sunlight and cool the atmosphere. While such proposals are rightly met with skepticism - if not fear - we should acknowledge that burning fossil fuels, deforestation and cultivation are inadvertent forms of "reverse geoengineering." The American soil scientist Rattan Lal and others argue that restoring vegetation on degraded lands and increasing soil organic carbon (SOC) on existing farmland has the potential to sequester sufficient CO2 to substantially mitigate climate change if done on a large scale. This form of "soft geoengineering" is a safe, win-win solution, since land restoration and soil improvement also restore watersheds, foster biodiversity, improve productivity and assist with rural poverty reduction. The potential to reduce climate change by sequestering atmospheric C02 in soil and vegetation is huge.Photosynthesis converts 112 billion tons of atmospheric CO2 into biomass annually. (By comparison, only nine billion tons of carbon emissions are produced from fossil fuel combustion.) However, almost all of the CO2 synthesized by plants is returned back to the atmosphere through plant and soil respiration.According to Lal, if 10 per cent of what plants photosynthesize annually - about 11 billion tons - could be retained in the biosphere, it would be possible to balance the global carbon budget, halting climate change. Lal explains that the atmospheric concentration of CO2 from fossil-fuel combustion and land-use changes has increased by 30 per cent since 1750, resulting in gradual global warming. Since the Industrial Revolution, global emissions of carbon are estimated at around 270 billion tons due to fossil-fuel combustion and about 136 billion tons due to land-use change and soil cultivation.Emissions due to land-use change include those from deforestation, biomass burning, conversion of natural ecosystems to agriculture, drainage of wetlands and soil cultivation. Depletion of the SOC pool has contributed around 78 billion tons of carbon to the atmosphere. Some cultivated soils have lost one-half to two-thirds of the original SOC.The depletion of SOC is accentuated by soil degradation and exacerbated by land misuse and soil mismanagement. Soil is the third-largest carbon sink after oceans and fossil fuels. Soil contains 4.5 times the sequestration capacity of all vegetation (including trees) and 3.3 times that of the atmosphere.While Rattan Lal estimates that 10 to 20 per cent of annual greenhouse gas emissions could be removed each year by sequestering carbon in cultivated land, a study by the Rodale Institute was more optimistic. It states, "multiple research efforts verify that practical organic agriculture if practised on the planet's 3.5 billion tillable acres, could sequester nearly 40 per cent of our current CO2 emissions." Even by the more conservative estimate, carbon farming holds significant potential to mitigate climate change. The global potential of SOC sequestration through the application of recommended management practices on a large scale, at an average of one ton per hectare year, is one billion tons of carbon per year, which would offset one-fourth to one-third of the total human-caused annual net increase in atmospheric CO2, estimated at 3.3 billion tons per year.The cumulative potential of SOC sequestration over 25 to 50 years could be as much as 60 billion tons, close to half of all emissions from land-use changes since 1750.The potential of soil sequestration to mitigate climate change of course depends on the extent of the application of recommended practices. Some 1.5 billion hectares of land are currently under cultivation. There is an optimum range of SOC concentration of two to three per cent in the root zone of most soil types. Given that cultivation has generally led to substantial decreases in SOC, most soils can benefit from increased SOC formation. On top of that is the vast potential to increase SOC formation in billions of hectares of deforested, degraded and desertified lands should they be reclaimed. © Copyright (c) The Starphoenix -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
