Tuesday, June 19, 2007

The Missing Sink! (We know what it is...)

Climate scientists have been puzzled by a strange phenomenon: the world is emitting 3GT CO2e more than it is officially sequestering. That 3GT (3 billion tonnes) has gone missing - and the World Bank says the missing load is getting bigger. Somehow it is being captured and stored by a "mystery sink" and the scientists don't know what it is.

Atmospheric increase 3.2 (±0.2) =
Emissions from fossil fuels 6.3 (±0.4) +
Net emissions from changes in land use 2.2 (±0.8) -
Oceanic uptake 2.4 (±0.7) -
Missing carbon sink 2.9 (±1.1)

They have tried a series of hypotheses: deforestation wasn't as bad as scientists originally declared it would be; the oceans are sequestering more than the scientists declared it would be; an unanticipated CO2 fertilising effect is making plants more effective as sinks; etc. Sedimentologists suggested that erosion was carrying soil organic carbon away and depositing it in creek beds where it is covered by sediments while new SOC is made by plants. Soil scientists (Rattan Lal) treat this suggestion as pure fantasy. Then there are the peat bogs in boreal forests in the northern hemisphere, which contain 10% of all carbon fixed on land, say the scientists, confidently in one breath, and in another: "How the bog stores carbon, in what quantity ... is completely unknown." In all these cases, science is clearly floundering. Several groups suggested the silent sequesterer is grazing soil. “Soil is where it’s at,” said Jeffrey Andrews of Duke University in Durham, N.C. at the annual meeting of the Ecological Society of America in 1993. He reported that trees take large amounts of carbon dioxide from the air and pump it into the ground. The Co2 eventually leaches into groundwater; this prevents it from quickly reentering the atmosphere. In 1994, scientists at the International Center for Tropical Agriculture (CIAT) declared that soils under South American savannas were the missing sink. Deep-rooted grasses may remove as much as 2 billion tons of carbon dioxide from the atmosphere yearly, said Dr. Myles Fisher, CIAT ecophysiologist."Green plants are small factories that use carbon dioxide, or CO2, and sunlight to produce organic matter. The perennial grasses Andropogon gayanus and Brachiaria humidicola convert as much as 53 tons of CO2 per hectare yearly to organic matter," he said. The storage of organic matter was not noticed earlier because the extensive roots of these grasses deposit it as deep as a meter in the savanna soil, Fisher explains. A decade later Steven Wofsy, an atmospheric scientist at Harvard University, concluded grassland soils were part of the answer, alongside oceans and forests.

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