How Green are Biofuels?

Biofuels are often touted as a way of efficiently generating power with lower effects on the environment than existing fuel production methods. But how effective are they if you weigh everything up? A paper by Lucas Reijnders in CAB Reviews looks at life-cycle assessments of biofuels and finds that they are much less efficient than solar cells in energy conversion, and some perform worse that conventional fossil fuels in emission of chemicals contributing to acidification and eutrophication. Some even appear set to worsen climate change.

Life-cycle assessments are very complex to do, because it is hard to work out what effects to rule in or out and on what basis to make comparisons. Factors such as what the land was previously used for need to be taken into account. Thus fuel from sugarcane grown on cleared Cerrado savannah has a lower net effect on greenhouse gas emissions than conventional diesel, but if a rainforest is being cleared, the biofuel does worse than diesel. Biofuels look much better if grown on land that isn’t currently absorbing much CO2. Reijnders, from the Institute for Biodiversity and Ecosystem Dynamics at the University of Amsterdam, points out that incentives may be needed to encourage the use of abandoned soils rather than clearing rainforest, as the rainforest clearance gives producers income from the sale of timber.

The input of fuel into producing biofuel needs to be estimated. Reijnders concludes that total fossil-fuel demand is relatively high for ethanol produced from European grain or US maize, and relatively low for palm oil or ethanol from sugarcane. However, palm oil tends to do worse than fossil fuel in greenhouse gas emissions.

“The ‘seed-to-wheel’ emissions of greenhouse gases associated with current transport biofuels are often higher than the corresponding life-cycle emissions of conventional fossil fuels”, says Reijnders. “Palm oil and ethanol from maize and wheat may contribute to energy security, but are counterproductive in limiting climate change,” he writes.

‘Transport biofuels – a life-cycle assessment approach’ by Lucas Reijnders, CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2008, 3, No. 071

Climate Change – What Will Happen to Weeds and Diseases?

Much attention has focused on what plants will be able to grow where as the effects of climate change are felt. A key factor that plays into that analysis is what effect climate change will have on diseases and weeds.Two new papers in CAB Reviews look at those two elements and show that that the picture is a complex and sometimes surprising one.

Sukumar Chakraborty (from CSIRO Plant Industry) and co-authors note that modelling experiments suggest that the range of key pathogenic fungi may shift significantly towards the poles as a result of global warming. The impacts of raised CO2 and temperature together are more difficult to estimate, as raised CO2 may increase the vigour of some trees and crops. From certain studies it seems that C3 plants, such as cereals, may suffer from increased numbers of pathogens with increased CO2, while C4 plants (most other crops and trees) may not. Chakraborty and colleagues write that minor changes in climate can tip the balance in favour of an exotic species, and the same may be true of disease outbreaks. Import risk analysis will need to take into account changes in the risks of establishment of pests and pathogens as the climate alters.

Examining the 12 most serious weeds, Xianshong Wang (from Indiana University-Purdue University Indianapolis) and Jacqueline Mohan (from the University of Georgia) suggest the competitiveness of weeds at higher temperatures and CO2 levels may be affected greatly by water availability. Most of the weeds will be expected to be boosted by rising temperatures. Field bindweed may become a more serious weed in drier regions, while it may be outcompeted in well-watered soils. Purple nutsedge may suffer because of expected reductions in moisture and rising soil nitrogen.

Wang and Mohan point out that the move to biofuels may exacerbate some of the projected weed problems: “Altered land use and the unforeseen consequences of energy plants may have a greater impact on the seriousness and injuriousness of weeds and weed-crop interactions than the effects of other global environmental changes, including rising CO2, global warming and more frequent and severe droughts.”

Effects of global environmental changes on weeds by Xianzhong Wang, J.E .Mohan
CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2008, 3, No. 067, 20 pp.

Impacts of global change on diseases of agricultural crops and forest trees by S. Chakraborty, J .Luck, G. Hollaway, A. Freeman, R. Norton, K.A. Garrett, K. Percy, A. Hopkins, C. Davis, D.F. Karnosky
CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2008, 3, No. 054, 15 pp.