Re: [Marxism] land use and global warming (was: Freeman Dyson ...)

[Les Schaffer <schaffer@xxxxxxxxxxxxx>]

Bob:

> One minor point:

ok, i won't be so knee-jerk in response to Dyson next time   ;-)

more on land use, biofuels, and carbon mitigation in yesterday's
Science, you might find interesting. snippets below, talk about
inefficiency of ethanol production, soil depletion, and so forth.

Les

==== carbon mitigation ====

Science 17 August 2007: Vol. 317. no. 5840, p. 902 DOI:
10.1126/science.1141361
   
Policy Forum
ENVIRONMENT:

Carbon Mitigation by Biofuels or by Saving and Restoring Forests?
Renton Righelato and Dominick V. Spracklen

Choosing from among the host of strategies for mitigation of
anthropogenic carbon emissions is not easy. There are competing
environmental priorities, social and economic factors, and commercial
and political interests. One strategy that has received extensive
attention is the use of biofuels for transport, particularly ethanol
from fermentation of carbohydrate crops as a substitute for petrol and
vegetable oils in place of diesel fuel. Such an approach would require
very large areas of land in order to make a significant contribution to
mitigation of fossil fuel emissions and would, directly or indirectly,
put further pressure on natural forests and grasslands. There are
numerous assessments of the relative merits of different liquid biofuel
strategies (e.g., 1-3), but few compare these with other uses of land (4).

Two issues need to be addressed before the efficacy of biofuels can be
assessed: the net reduction in fossil carbon emissions (avoided
emissions) arising from use of agriculturally derived biofuels and the
effect of alternative land-use strategies on carbon stores in the
biosphere. As land is the limiting resource, the appropriate basis for
comparison is a function of land area (Mg C ha-1 year-1). We use a
period of 30 years as a basis for comparing strategies because it is
likely to take that much time for carbon-free fuel technologies to be
developed and introduced. Estimates of avoided emissions vary widely
depending on crop, fuel type, and conversion technology used; some
typical examples derived from lifecycle analyses are shown in the figure
(right). In these analyses, no allowance has been made for emissions
arising from change in land use to produce the fuel crop. In all cases,
forestation of an equivalent area of land would sequester two to nine
times more carbon over a 30-year period than the emissions avoided by
the use of the biofuel. Taking this opportunity cost into account, the
emissions cost of liquid biofuels exceeds that of fossil fuels.

Moreover, large areas of land would be needed to make significant
quantities of fuel. A 10% substitution of petrol and diesel fuel is
estimated to require 43% and 38% of current cropland area in the United
States and Europe, respectively (5). As even this low substitution level
cannot be met from existing arable land, forests and grasslands would
need to be cleared to enable production of the energy crops. Clearance
results in the rapid oxidation of carbon stores in the vegetation and
soil, creating a large up-front emissions cost (6) that would, in all
cases examined here, outweigh the avoided emissions.

Of the biofuel sources shown, only conversion of woody biomass (1, 2, 4,
7) may be compatible with retention of forest carbon stocks. Woody
biomass can be used directly for fuel or converted to liquid fuels.
Although still in a development stage, avoided emissions in temperate
zones appear similar to assimilation by forest restoration. Moreover, it
may be possible to avoid environmental problems associated with
extensive monoculture (8) by harvesting from standing forests. In this
case, soil and above-ground carbon stocks may be built up in parallel
with sustainable harvesting for fuel production.

If the prime object of policy on biofuels is mitigation of carbon
dioxide-driven global warming, policy-makers may be better advised in
the short term (30 years or so) to focus on increasing the efficiency of
fossil fuel use, to conserve the existing forests and savannahs, and to
restore natural forest and grassland habitats on cropland that is not
needed for food. In addition to reducing net carbon dioxide flux to the
atmosphere, conversion of large areas of land back to secondary forest
provides other environmental services (such as prevention of
desertification, provision of forest products, maintenance of biological
diversity, and regional climate regulation), whereas conversion of large
areas of land to biofuel crops may place additional strains on the
environment. For the longer term, carbon-free transport fuel
technologies are needed to replace fossil hydrocarbons.

References

   1. Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains
in the European Context [European Council for Automotive R&D (EUCAR),
European Commission Joint Research Center (JRC), and Conservation of
Clean Air and Water in Europe (CONCAWE) joint study, Brussels, May
2006); http://ies.jrc.ec.europa.eu/wtw.html.
   2. E. Larson, "A review of LCA studies on liquid biofuels for the
transport sector," Scientific and Technical Advisory Panel of the Global
Environment Facility (STAP) workshop on Liquid Biofuels, 29 August to 1
September 2005, New Delhi, India;
http://stapgef.unep.org/docs/folder.2005-12-07.8158774253/folder.2005-12-08.9446059805/.
   3. M. A. Elsayed, R. Mathews, N. D. Mortimer, Carbon and Energy
Balances for a Range of Biofuel Options (Resources Research Institute,
Sheffield Hallam University, Sheffield, UK, 2003).
   4. M. U. F. Kirschbaum, Biomass Bioenergy 24, 297 (2003).
   5. International Energy Authority, Biofuels for Transport: An
International Perspective (IEA, Paris, France, 2004), chap. 6;
www.iea.org/textbase/nppdf/free/2004/biofuels2004.pdf.
   6. R. T. Watson et al., Land Use, Land-Use Change and Forestry
(Intergovernmental Panel for Climate Change, Geneva, 2001), p 184.
   7. D. Tilman, J. Hill, C. Lehman, Science 314, 1598 (2006).
   8. S. Raghu et al., Science 313, 1742 (2006).

Supporting Online Material
www.sciencemag.org/cgi/content/full/317/5840/902/DC1

==== letters to the editor =====

Science 17 August 2007: Vol. 317. no. 5840, pp. 897 - 898 DOI:
10.1126/science.317.5840.897b

Biofuels and the Environment

In his Editorial "The biofuels conundrum" (27 April, p. 515), Donald
Kennedy describes how biofuels, although at first glance a boon for the
environment, have hidden costs that could prove environmentally and
socially disastrous. His solution is "to abandon this cluttered arena"
and to invest in research in plant physiology to overcome biomass
recalcitrance for cellulosic conversion. There are several problems with
this view. First, it is unlikely that a single approach will suit all
circumstances. For example, gasification techniques seem efficient and
promising for some feedstocks, but not all. Second, cellulosic
conversion demands uniform feedstocks, which translates into high-input
and environmentally destructive biofuel monocultures. Such monocultures
are unlikely to be sustainable. Third, given the evolutionarily
conserved structure of cell walls, it is possible that fooling with it
would lead to crops that are prone to structural failure or, more
likely, sensitivity to fungal pathogens.

More research into plant physiology may help solve some of these
problems, but perhaps some of our money is better spent supporting plant
ecology. We already know that diverse grasslands can outperform
monocultures in biofuels production (1). We also know that such
grasslands are being lost or degraded worldwide because of a lack of
active management. Learning how to use such grasslands sustainably for
biofuels will not only reduce greenhouse gas emissions but also promote
biodiversity. But we must first move away from a crop-based mentality
and rely on expertise from a much broader scientific base than is
currently being considered.

Michael W. Palmer
Department of Botany
Oklahoma State University



Donald Kennedy's Editorial "The biofuels conundrum" (27 April, p. 515)
is timely and needed. However, we have two concerns. The first is that
the suggested use of corn stover as a source for ethanol fuel has
serious environmental implications. U.S. agriculture is currently losing
topsoil 10 times faster than sustainability (1). Removing corn stover
and/or leaving the soil unprotected will intensify soil erosion 10-fold
or more (2). Without the protection of crop residues, soil loss may
increase as much as 100-fold (3). Increasing soil erosion also
intensifies the global warming problem and other problems (4, 5).

Another concern is the fact that green plants collect little solar
energy, an average of only 0.1% per year (6). Photovoltaics, in
contrast, collect 10 to 20% of the solar energy or 100 to 200 times the
rate of green plants (6).

Crops, forestry, and other green plants collect a total of 53 exajoules
of solar energy per year from sunlight (7). However, Americans consume
more than twice this amount of fossil fuel energy each year (8). Some
suggest that ethanol produced from corn and cellulosic biomass could
replace 30% of the oil used in the United States (9). Yet the 20% of the
U.S. corn crop now converted into 5 billion gallons of ethanol replaces
1% of U.S. petroleum consumption (6). Ethanol yield from sugar is
better, as documented in Brazil (Kennedy points this out), but the
environmental, economic, and social costs are enormous. Soil erosion
associated with sugarcane is greater than any other crop grown in Brazil
(10).

David Pimentel
Cornell University

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