Environmental Engineering Reference
In-Depth Information
BOX 5.2 CLIMATE CHANGE IMPACTS ON GLOBAL CEREAL PRICES
Several modeling groups have analyzed future changes in global cereal markets in response
to climate change. All operate by making estimates of yield responses in each region, and then
inputting these into a model of global trade that computes the optimal mix of crop areas in
different regions and the market-clearing price. Five models summarized by the recent IPCC
report suggests small price changes for warming up to 2.5°C, and a nonlinear increase in prices
thereafter (Easterling et al., 2007). Two important caveats relate to these estimates, however.
First, the yield changes used in these models usually assume considerable levels of farm-
level adaptations, which substantially reduce impacts. For example, in one prominent study
cereal prices rose by 150% for a 5.2°C global mean temperature rise if farm-level adaptations
were not included. When changes in planting dates, cultivar choices, irrigation practices, and
fertilizer rates were simulated, these price changes were reduced to roughly 40% (Rosenzweig
and Parry, 1994). Other studies often do not estimate impacts without adaptation, making it dif-
ficult to gauge assumptions. The costs of adaptation are also not considered in these studies, or
reflected in price changes.
Second, most assessments have not adequately quantified sources of uncertainty. Although
different climate scenarios are often tested, processes related to crop yield changes and eco-
nomic adjustments are often implicitly assumed to be perfectly known. An additional source of
uncertainty is potential competition with bio-energy crops for suitable land, which could limit
the ability of croplands to expand in temperate regions as simulated by most trade models.m
5.2 COASTAL EROSION AND FLOODING
Ourknowledgeofthelinksbetweenatmosphericconcentrationlimits,
trajectories toward equilibrium temperature change, and sea level rise is
fraught with uncertainty. As reported in Section 4.8, it is therefore only
possibletoofferarangeofsealevelrisebetween0.5and1.0mthrough
2100.
Movingdownthecausalchaintoconsidercoastalerosionandflooding
addsyetanotherlayerofcomplicationbecausebotharedrivenprimarilyby
stormsurges,land-usedecisions,andotherprocesseswhoseintensitiesand
frequencieschangefromplacetoplace.Thesechangesalterthecharacters
ofassociatedrisksevenifchangesintheintensitiesandfrequenciesofthe
storms,themselves,cannotbeprojected.Thesocialandeconomicramifica-
tionsofthesephysicalmanifestationsofclimatechangedependcritically
onpatternsoffuturedevelopmentandpopulationgrowth.Itis,therefore,
extremelydifficulttooffercrediblebroad-basedestimatesofvulnerabilities
andpotentialadaptationcosts.Atbest,infact,wecanofferonlysuggestive
