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Showing posts with label biofuels global warming Science fossil fuels. Show all posts
Showing posts with label biofuels global warming Science fossil fuels. Show all posts
Oct 22, 2008
Sep 27, 2008
Recap:Water: The High Plains Aquifer
The High Plains aquifer underlies one of the most productive agricultural regions in the US. This region is semi-arid and does not get much precipitation, therefore most of the water used for irrigation is drawn from wells. Ground water levels here have been dropping and I thought of doing a zeroth order analysis of how many years will the water in the aquifer last. I used water level change data from USGS. According to USGS, there has been no major change in area under irrigation from 1988-2002. This report also points out that the total change in ground water storage from 1988-2000 was 47 million acre-feet and that the total ground water storage (estimated) in 2000 was 2970 million acre-feet. If we assume that ~30% of this water is recoverable, this gives us an approximate lifetime of 230 years (assuming that the irrigated acreage does not increase). However, the irrigated acreage did increase from 2002-2003, and the rates of depletion are approximately twice their value from 1988-2002. A map showing generalized water-level changes in the aquifer from 2002-03 are shown in the report. As expected, there is a lot of heterogeneity in the way water-levels dropped. Parts of central and south High Plains underwent more drastic water-level changes compared to their northern counterparts. Accordingly, the area-weighted water-level changes per state were more pronounced in Kansas, New Mexico, Oklahoma, and Texas compared to Colorado and Nebraska. Therefore, even if the water might still be around for another 2 centuries, parts of the High Plains might be facing depleted ground water levels sometime soon. These water-level changes might have important implications for US food supply.
Feb 10, 2008
Can biofuels cause global warming ?
A recent biofuels study published in Science points that the use of natural lands for growing biofuels leads to more CO2 emissions compared to the case where no forest lands are cleared. In an interview about a related topic, another scientist points out that using biofuels over fossil fuels actually increases CO2 emissions because the soil carbon released to the atmosphere. There however are are some ppl who disagree with the study's findings, citing uncertanities in modeling the soil carbon cycle arising out of land use changes (tilling, fertilizer use etc..) as one of the study's main weaknesses. Soil carbon turnover rates in the tropics are be much higher than those in temperate climates. I guess that this is one of the key issues the Science study tried to address; they used a global agricultural model to estimate these emissions. The use of waste biomass (ex: from forests) and producing biofuels without converting additional natural habitats to farmland, will not cause additional CO2 emissions.
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