GHG atmospheric concentrations are measured in parts per million (ppm). Current levels in the atmosphere are below 400 ppm, and long-term levels above 500 could lead to serious economic and social disruption. In the immediate pre-industrial revolution era concentrations were in the 250 ppm range. Hence 500 ppm represents the ‘doubling’ factor that is so frequently discussed in the media.
GHGs are augmented by the annual additions to the stock already in the atmosphere, and at the same time they decay—though very slowly. GHG-reduction strategies that propose an immediate reduction in emissions are more costly than those aimed at a more gradual reduction. For example, a slower investment strategy would permit in-place production and transportation equipment to reach the end of its economic life rather than be scrapped and replaced ‘prematurely’. Policies that focus upon longer term replacement are therefore less costly.
While not all economists and policy makers agree on the time scale for attacking the problem, most agree that, the longer major GHG reduction is postponed, the greater the efforts will have to be in the long term—because GHGs will build up more rapidly in the near term.
A critical question in controlling GHG emissions relates to the cost of their control: how much of annual growth might need to be sacrificed in order to get emissions onto a sustainable path? Again estimates vary. The Stern Review proposed that, with an increase in technological capabilities, a strategy that focuses on the relative near-term implementation of GHG reduction measures might cost “only” a few percentage points of the value of world output. If correct, this may not be an inordinate price to pay for risk avoidance in the longer term.
Nonetheless, such a reduction will require particular economic policies, and specific sectors will be impacted more than others.
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