The sectoral effects of mitigation on agriculture and forestry are described in detail in Chapter 4. This section covers ancillary benefits for agriculture.
GHG mitigation strategies that also reduce emissions of ozone precursors, i.e.,
volatile organic compounds (VOCs) and nitrogen oxides (NOx), may
have ancillary benefits for agriculture. Elevated concentrations of tropospheric
ozone (O3) are damaging to vegetation and to human health (EPA, 1997).
GHG mitigation strategies which increase efficiency in energy use or increase
the penetration of non-fossil-fuel energy are likely to reduce NOx
emissions (the limiting precursor for O3 formation in non-urban areas)
and hence O3 concentrations in agricultural regions.
Studies of the adverse impacts of O3 on agriculture
were first conducted in the United States in the 1960s, with major studies in
the 1980s (EPA, 1997; Preston et al., 1988) and later in Europe (U.K.
DoE, 1997) and Japan (Kobayashi, 1997). These studies indicate that, for many
crop species, it is well established that elevated O3 concentrations
result in a substantial reduction in yield. The US Environmental Protection
Agency (EPA) funded the National Crop Loss Assessment Network (NCLAN) from 1980
to 1986, which developed O3 dose-plant response relationships for
economically important crop species (Heck et al., 1984a and b). Results
of this study are shown in Figure 9.3. The basic NCLAN
methodology was used in 9 countries in Europe between 1987 to 1991 on a variety
of crops including wheat, barley, beans, and pasture for the European Crop Loss
Assessment Network (EUROCLAN) programme. EUROCLAN found yield reductions to
be highly correlated with cumulative exposure to O3 above a threshold
of 30-40 parts per billion (ppb) (Fuhrer, 1995).
The World Health Organization (WHO) uses the AOT 40 standard to describe an
acceptable O3 exposure for crops. AOT 40 is defined as the accumulated
hourly O3 concentrations above 40 ppb (80 mg/m3) during
daylight hours between May and July. Acumulative exposure less than 6000 mg/m3.h
is necessary to prevent an excess of 5% crop yield loss (European Environment
Agency, 1999). Observations indicate that this limit is exceeded in most of
Europe with the exception of the northern parts of Scandinavia and the UK (European
Environment Agency, 1999). Median summer afternoon O3 concentrations
in the majority of the eastern and southwestern United States presently exceed
50 ppb (Fiore et al., 1998). As shown in Figure 9.3
these concentrations will result in yield reductions in excess of 10% for several
crops. IPCC Working Group (WG)I (Chapter 4) predicts that, if emissions follow
their SRES A2 scenario, by 2100 background O3 levels near the surface
at northern mid-latitudes will rise to nearly 80ppb. (However, scenario B1 has
only small increases in O3 emissions.) At the higher O3
concentrations the yield of soybeans may decrease by 40%, and the yield of corn
and wheat may decrease by 25% relative to crop yields at pre-industrial O3
levels. Within a crop species, the sensitivity of individual cultivars to O3
can vary (EPA, 1997), and it is possible that more resistant strains could be
utilized. However, this would impose an additional constraint on agriculture.
An economic assessment of the impact of O3 on US agriculture, based on data from the NCLAN study, found that when O3 is reduced by 25% in all regions, the economic benefits are approximately US$1.9billion (bn) (1982 dollars) (Adams et al., 1989). Conversely, a 25% increase in O3 pollution resulted in costs of US$2.1bn (Adams et al., 1985). Two recent studies found that crop production may be substantially reduced in the future in China owing to elevated O3 concentrations (Chameides et al., 1999; Aunan et al., 2000, forthcoming). Chinas concerns about food security may make GHG mitigation strategies that reduce surface O3 concentrations more attractive than those that do not.
Chapter 3 considers new technologies for using biomass, such as sugar cane, to replace fossil fuels. Such mitigation may have considerable associated benefits, particularly for sustainable development in creating new employment (see 126.96.36.199 below).
Alig et al. (1997) through modelling alternative carbon flux scenarios using the forestry and agricultural sector optimization model (FASOM) estimated the welfare effects of carbon sequestration for the US. They estimate total social welfare costs to range from US$20.7bn to $50.8bn. In the case of the agricultural sector, the consumers surplus decreases in all scenarios.
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