In an altered state, I was thinking that any soil that could yield significant biofuel would also naturally act as a large sink of carbon. To put it another way, if you see a bunch of ugly weeds on a dry field, don't think you are going to magically convert that to biofuel without significant inputs, as that land probably sucks. But the good land is mostly taken, by either nature or agriculture.
So assuming you want decent yields, you will need to clear out some land--preferably without starving people. This means you essentially have to target some of the best natural carbon sinks (or the best required to provide land for maximum yields, since marginal yields need more land). And I wondered if anyone has put a number on exactly how much carbon you are releasing when you cultivate it and turn it into a carbon recycler (its not a sink, as all collected carbon would be burned in a cycle). It turns out, a couple have.
Increasing energy use, climate change, and carbon dioxide (CO2) emissions from fossil fuels make switching to low-carbon fuels a high priority. Biofuels are a potential low-carbon energy source, but whether biofuels offer carbon savings depends on how they are produced. Converting rainforests, peatlands, savannas, or grasslands to produce food crop–based biofuels in Brazil, Southeast Asia, and the United States creates a “biofuel carbon debt” by releasing 17 to 420 times more CO2 than the annual greenhouse gas (GHG) reductions that these biofuels would provide by displacing fossil fuels. In contrast, biofuels made from waste biomass or from biomass grown on degraded and abandoned agricultural lands planted with perennials incur little or no carbon debt and can offer immediate and sustained GHG advantages.
Land Clearing and the Biofuel Carbon Debt
For the two most common ethanol feedstocks, the study found that sugarcane ethanol produced on natural cerrado lands would take ~17 years to repay its carbon debt, while corn ethanol produced on U.S. central grasslands would result in a repayment time of ~93 years. The worst-case scenario is converting Indonesian or Malaysian tropical peatland rainforest to palm biodiesel production, which would require ~420 years to repay.
Wiki ILUC
So, if we were to switch to biofuel tomorrow, we would have to release immediately the carbon from 15 billion acres (needed to replace dirty oils) of some of the best sinks, causing a massive carbon emissions increase that could not even be negated for decades when we are already in the pressure cooker (needing instant reduction in atmospheric co2). Further, you actually reducing the ability of the earth to capture carbon, as you are converting good carbon storage land into carbon recycling land.
So if it takes a hundred or so years to get back to today's 400 ppm baseline, can humanity wait that long to pay back this carbon debt?
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