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360 | IAASTD Global Report

Table A.5.3 Overview of major uncertainties in IMAGE 2.4

Model component

Uncertainty

Model structure

•   TIMER Energy model: Integration in larger economy and dynamic formulation in energy model (learning by doing)
•   Land model: Rule-based algorithm for allocating land use
•   Environmental system: Scheme for allocating carbon pools in the carbon cycle model

Parameters

•   Energy: Resource assumption and learning parameters
•   Land: Biome model parameter setting and CO2 fertilization
•   Environment: Climate sensitivity, climate change patterns and multipliers in climate model (Leemans et al., 2002)

Driving force

•   Income growth (GDP)
•   Population growth
•   Assumptions on technology change in energy model
•   Environmental policies

Initial condition

•   Emissions in base year (2000)
•   Historic energy use
•   Initial land use/land cover map
•   Historical land use data (from FAO)
•   Climate observations in initial year

Model operation

•   Downscaling method in climate change model (Eickhout et al., 2004)

 

     The carbon cycle model has also recently been used for a sensitivity analysis to assess uncertainties in carbon cycle modeling in general (Leemans et al., 2002). Finally, a main uncertainty in IMAGE's climate model has to do with (1) "climate sensitivity," i.e., the response of global tem­perature computed by the model to changes in atmospheric greenhouse gas concentrations, and (2) regional patterns of changed temperature and precipitation. IMAGE 2.2 has actually been set up in such a way that these variables can be easily manipulated on the basis of more scientifically-de­tailed models. To summarize, most of IMAGE would need to go into the category of established but incomplete knowl­edge (Table A.5.4).

 

A.5.3 The Global Trade and Environment Model (GTEM)

A.5.3.1Introduction
GTEM has been developed by the Australian Bureau of Ag­ricultural and Resource Economics  (ABARE)  specifically to address policy issues with global dimensions and issues where the interactions between sectors and between econo­mies are significant. These include issues such as interna­tional climate change policy, international trade and invest­ment liberalisation and trends in global energy markets.

Table A.5.4 Level of confidence in different types of scenario calculations from IMAGE

Level of Agreement/ Assessment

High Low

Established but incomplete •   Climate impacts on agriculture and biomes
•   Carbon cycle Speculative
•   Grid-level changes in driving forces
•   Impacts of land degradation

Well established •   Energy modeling and scenarios
Competing explanations
•   Global climate change, including estimates of uncertainty
•   Local climate change •   Land use change

 

Low

High

Amount of evidence (theory, observations, model outputs)

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