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Reframing the climate change challenge (changes)

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Contents

Idea

Reframing the climate change challenge in light of post-2000 emission trends is a 2008 paper by K. Anderson and A. Bows. It questions the common way of framing of climate change policy in terms of keeping the rise of global temperatures below 2°C.

They claim that accomplishing this goal would require a “sea change in political orthodoxy”, since it would require, at least, global energy related emissions to peak by 2015, rapidly decline at 6–8 per cent per year between 2020 and 2040, and for carbon emissions to completely end soon after 2050. In fact, they say:

the current framing of climate change cannot be reconciled with the rates of mitigation necessary to stabilize at 550 ppmv CO2e and even an optimistic interpretation suggests stabilization much below 650 ppmv CO2e is improbable.

Here ‘CO2e’ means CO2 equivalent, including other greenhouse gases.

Details

According to these authors, the problem is that:

According to a recent synthesis of global climate models (Meinshausen 2006, table 28.1), the 550 ppmv CO2e concentration, around which much policy discussion revolves, suggests an 82 per cent mid-value probability of exceeding 2°C. By contrast, to provide a 93 per cent mid-value probability of not exceeding 2°C, the concentration would need to be stabilized at, or below, 350 ppmv CO2e, i.e. below current levels. While Meinshausen’s analysis demonstrates the gulf between the science and the policy of approximately 2°C, the analysis within the IPCC’s fourth assessment report (IPCC 2007a), hereafter AR4, suggests that the scale of the challenge is even more demanding. Not only has the ‘best estimate’ of climate sensitivity risen from 2.5°C in the 1996 report (IPCC 1996, p. 39) to 3°C in AR4, but also the inclusion of carbon-cycle feedbacks has significantly reduced the cumulative anthropogenic emissions (carbon budget) associated with particular concentrations of CO2e (IPCC 2007a, topic 5, p. 6).

They say that even assuming the IPCC’s optimistic estimate that keeping CO2 equivalent levels below 450 ppm, the necessary 4 per cent per year reductions in CO2e emissions beginning by 2018 are “unlikely to be politically acceptable without a sea change in the economic orthodoxy”. They conclude:

While this analysis suggests stabilizing at 450 ppmv is theoretically possible, in the absence of an unprecedented change in the global economic model and the rapid deployment of successful CO2 scrubbing technologies, 450 ppmv is no longer a viable stabilization concentration. The implications of this for climate change policy, particularly adaptation, are profound. The framing of climate change policy is typically informed by the 2°C threshold; however, even stabilizing at 450 ppmv CO2e offers only a 46 per cent chance of not exceeding 2°C (Meinshausen 2006). As a consequence, any further delay in global society beginning down a pathway towards 450 ppmv leaves 2°C as an inappropriate and dangerously misleading mitigation and adaptation target.

According to the analysis in this paper, stabilizing at 450 ppmv requires, at least, global energy related emissions to peak by 2015, rapidly decline at 6–8 per cent per year between 2020 and 2040, and for full decarbonization sometime soon after 2050. The characteristics of the resulting 450 ppmv scenario are summarized in this table:

450 ppm scenario
characteristics quantity
total GtCO2e 858
peak in CO2e emissions2015
post-peak annual CO2e decarbonization rate ∼4%
total decarbonization date (including forestry)∼2060–2075
post-peak sustained annual energy and process decarbonization rate∼6–8%
total energy and process decarbonization date∼2050–2060

This assumes that the most optimistic of the IPCC’s range of cumulative emission values is broadly correct.

References

category: reports, climate

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