Enciclopédia da Energia Natural   CPMA.COMUNIDADES.NET
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Enciclopédia da Energia Natural CPMA.COMUNIDADES.NET

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the effects of climate change are
underestimated. Finally, as Ricardian analyses are based on
statistical estimates, the same limitations as discussed for
econometric methods apply.
Crop yield studies are used as an input to estimate the
economic impact of climate change to simulate the impact of
climate change on economic outcomes. Models used to
26 Climate Change and Policy | Climate Change and Food Situation
estimate the economic impact of climate change are either
partial equilibrium models or general equilibrium models.
Partial equilibrium models consider only one economic
sector \u2013 in this context, the agricultural sector \u2013 but take into
account a wide range of economic and institutional forces. The
precision with which markets are detailed depends on the level
of disaggregation. All models determine profit maximizing
input and output bundles. Cross-sectoral interactions are ig-
nored by partial equilibrium models and therefore climate
change impacts in one sector do not alter resource allocations
in other sectors. This limitation is not serious in industrialized
and semi-industrialized countries given the relatively small
share of agricultural output in their national economies, but
may be significant in other countries. The consideration of
only certain countries or regions constitutes another con-
straint, as bilateral trade flows are not represented and changes
in international commodity prices are not accounted for.
Global assessment studies use computable general equilibrium
(CGE) models to capture interactions between the agricultural
sector and other economic sectors. The inter-sectorial nature of
these models allows the simulation of economic activity
through incomes and expenditures. Furthermore, CGE models
include international trade flows, which allow these models to
account for inter-regional effects. One of the weaknesses of
general equilibrium models is the calibration of the economic
model. Typically, CGE models are assigned to fit production
data for a single year and some parameters are \u2018guesstimated.\u2019
Another shortcoming relates to the imprecise representation of
the different economic sectors in countries considered. That is,
as CGE models include all sectors, the sectoral detail of pro-
duction functions is often less sophisticated than in partial
equation models. Choices regarding crops considered as
input in the CGE model also have large influences on results.
The omission of important crops can significantly bias the
results. Alternatively, considering only crops highly sensitive
to weather conditions (e.g., wheat and maize) constitutes an-
other form of selection bias. The global impact analyses that
focus only on those crops are likely biased in favor of predict-
ing revenue losses. The consideration of less sensitive crops,
such as irrigated crops adapted to warmer climates, mitigates
these results by representing potential gains induced by climate
warming. Finally and most importantly, many economic
models assume that crop areas are completely exogenous and
treat agricultural land as a fixed factor. These models, therefore,
simply reallocate crop land among existing uses.
The estimation of such an ensemble of effects is compli-
cated due to the numerous interaction effects. Integrated
assessment modeling frameworks, which couple economic
models with ecosystem and climate models, are better suited
to represent the complex interactions and feedbacks of the
global system and therefore provide better estimates of climate
change impact on food.
Literature Review of Impact Assessments
The methods described above have been used extensively to
estimate the effect of climate change on crop production and
food supply. The most direct effect of climate change is on crop
yields. Extreme temperature and precipitation have a negative
effect on crop yields, but the net effect of climate change on
crop yields is dependent on the crops and the regions consid-
ered. Most studies find that while crop growth will be nega-
tively affected by temperature increases in temperate regions,
crop yields in cold regions are expected to benefit from tem-
perature increases. CO2 concentration in the atmosphere will
also improve crop yields through a CO2 fertilization effect.
When combining this fertilization effect with climate change,
studies predict higher crop yields than when only considering
the impact of climate change, even under relatively high warm-
ing scenarios.
Climate change will also have indirect effects on crop yields.
For instance, global warming will benefit crop productivity in
cold regions by lengthening the growing season. On the other
hand, temperature rises will favor pest and disease prolifera-
tion in tropical regions and entail further crop damage. Live-
stock is less sensitive to weather but is nonetheless vulnerable
to extreme events such as heat waves and droughts. Livestock
can also be indirectly affected through the effect of climate
change on feedstock crops.
Most early economic research focused on the aggregate
economic effects of climate change on agriculture. Crop yield
reductions result in an increase in crop prices and therefore
reduce consumer surplus. Therefore, consumers from regions
where yields are predicted to be negatively affected by climate
change will be penalized. The opposite effect is predicted in
regions where climate change will entail positive impacts on
yields. On the other hand, price changes will modify producer
surplus (revenue for farmers). A rise in food price will benefit
agricultural exporting regions but harm importing regions. But
these economic effects are different in developing countries. In
regions such as SSA, where food production is almost entirely
used for domestic consumption, a climate change induced
crop yield decrease is expected to result in an increase in land
use to compensate for the loss of production, although this
response will only partially offset the decrease in production
due to climate change.
Assessments of climate change damages to agriculture must
also consider adaptation measures at the global level. For
instance, a spatial shift of crop growing areas toward more
suitable regions will make the effect of decreased yields in
one region only temporary. Additionally, impact assessments
must consider the profitability of such measures in the context
of global agricultural markets. The development of irrigation
systems in regions predicted to become more drought-prone
can be justified if crop prices rise substantially. However, a
global crop price decrease may render this adaption system
uneconomical, even if irrigation restores crop yields. Finally,
as research interests evolve toward identifying viable adapta-
tion strategies, it is important to consider broader global
The latest studies estimate comprehensive environmental
impacts by considering a dynamic framework of agricultural
systems in the context of fluctuating economic growth,
population, and competing demands for land (including bio-
fuels and recreational activities). For instance, one study ana-
lyzed the impact of climate change, CO2 fertilization, and
ozone damages on agriculture. This study found opposite ef-
fects of ozone and climate change as ozone damages are pre-
dicted to be the largest in the northern temperate regions, while
these regions are expected to benefit from climate change.
Climate Change and Policy | Climate Change and Food Situation 27
Mitigation Policies and Their Impacts on Agriculture
and Food
Mitigation policies aim to reduce GHG emissions and increase
carbon sequestration in order to limit anthropogenic changes
in climate.