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Each step of projecting climatic variables includes uncertainties, but by choosing more than one Module
emission scenario, working with an ensemble of GCMs and using different techniques to obtain regional
projections, we could minimize these uncertainties to levels that enable us to use the projections to
indentify consequences of climate impacts and needed adaptations (for details see Table 2 and Figure
8). The results of these models provide estimates of how basic climatic variables will develop in the

future at the global or regional levels as a range of potential future impacts, all of which are equally
plausible. This means that decision-makers and practitioners will need to consider how to apply this
range of impacts to their area of interest in order to identify vulnerabilities and adaptation. However, the
important part of a climate change impact assessment should be not only obtaining information about
changes in basic climatic variables such as temperature and precipitation, but also to gather information Abu Dhabi, UAE
on their consequences on ecosystems and human well-being.

Table 2 Key steps and uncertainties when projecting climate change

Key steps Major outcomes Major uncertainties and how to address them
Projection of ? Scenarios of Assumptions about and relationships between future population,
future emissions population, energy, socio-economic development and technical changes are uncertain;
economic changes this can be addressed by making climate projections for a range of
these SRES emissions scenarios.

Concentration ? Carbon cycle and The imperfect understanding of the processes and physics in
of GHGs CO2, chemistry models the carbon cycle, chemical reactions in the atmosphere and
methane, feedback between climate, the carbon cycle and atmospheric
sulphates chemistry generates uncertainties in the conversion of emissions
to concentration of GHGs in the atmosphere. To reflect this
uncertainty in the climate scenarios, the use of atmosphere-ocean
general circulation models (AOGCMs) is needed.

Global climate ? Coupled global There is much we do not understand about the workings of the
change: climate models climate system, and hence uncertainties arise because of our
Temperature, incorrect or incomplete description of key processes and feedback
rainfall, sea level, in the model. This is illustrated by the fact that current global climate
etc. models, which contain different representations of the climate
system, project different patterns and magnitudes of climate change

Regional detail: ? Regional climate The climate varies on timescales of years and decades; for any given
Mountain effects, models period in the future (e.g., 2041–2070) natural variability could act to
islands, extreme either add to or subtract from changes (for example in local rainfall)
weather due to human activity. This uncertainty cannot yet be removed, but
it can be quantified. This is done by running ensembles of future
climate projections

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