文档介绍：PART II: The Impacts of Climate Change on Growth and Development
6 Economic modelling of climate-change impacts
Key Messages
The ary cost of climate change is now expected to be higher than many earlier studies
suggested, because these studies tended not to include some of the most uncertain but potentially
most damaging impacts.
Modelling the overall impact of climate change is a formidable challenge, involving forecasting
over a century or more as the effects appear with long lags and are very long-lived. The
limitations to our ability to model over such a time scale demand caution in interpreting results, but
projections can illustrate the risks involved – and policy here is about the economics of risk and
uncertainty.
Most formal modelling has used as a starting point 2 - 3°C warming. In this temperature range,
the cost of climate change could be equivalent to around a 0 - 3% loss in global GDP from what could
have been achieved in a world without climate change. Poor countries will suffer higher costs.
However, ‘business as usual’(BAU) temperature increases may exceed 2 - 3°C by the end of
this century. This increases the likelihood of a wider range of impacts than previously
considered, more difficult to quantify, such as abrupt and large-scale climate change. With 5 -
6°C warming, models that include the risk of abrupt and large-scale climate change estimate a 5 -
10% loss in global GDP, with poor countries suffering costs in excess of 10%. The risks, however,
cover a very broad range and involve the possibility of much higher losses. This underlines the
importance of revisiting past estimates.
Modelling over many decades, regions and possible es demands that we make
distributional and ethical judgements systematically and explicitly. Attaching little weight to the
future, simply because it is in the future (‘pure time discounting’), would produce low estimates of cost
– but if you care little