Geoscience Reference
In-Depth Information
For those interested in other modeling results, we can look to the
EMF-22 modeling comparison discussed in Part I. The eleven models ran
scenarios very similar to the two shown in Figure 26. The results were
roughly parallel. In the case of universal participation, about half the
models found that it was possible to attain the 2°C target. For partial par-
ticipation, twenty of twenty-two model runs found the 2°C target infea-
sible. In reality, “infeasible” means that it would require causing a horrible
economic depression. These results have been confi rmed by other model-
ers as well.
The models also estimated the costs of different scenarios. The costs
from the EMF models were generally higher than the DICE model cal-
culations shown in Figure 26. There were also large differences among
the models. If we take a scenario that was feasible for all the models,
the largest-cost model estimate for meeting the objective was twelve
times the minimum-cost model estimate.
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Why are the cost uncertainties so large? One reason is that models
use different cost structures: Some are top-down while others are
bottom-up. Additionally, they have different growth rates of output and
emissions. A model with a high growth rate has to spend much more to
get temperature down to the desired level. A third difference is the vi-
sion of energy technologies. For example, one model might see a con-
strained nuclear power industry, which would raise costs.
However, we should view these model differences as genuine and
not imaginary ones. They cannot be resolved by getting the modelers
together to insist that they fi nd the “right” answer. The cost estimates
refl ect carefully considered judgments about future economic and en-
ergy systems, and we should take them as refl ecting uncertainties about
the future as seen by the world's leading modeling teams.
So the bottom line on costs is this. Suppose we live in an ideal
world—one where countries work together cooperatively to introduce
emissions reductions, take care to ensure that all countries and sectors
participate, and time their actions effi ciently. For this world, slowing cli-
mate change to meet the Copenhagen objective of a 2°C limit or some-
thing close to it would be a feasible objective. Estimates from economic
