Efficiency improvements and structural changes in energy systems, that is, decarbonization, constitute the most resilient strategy in response both to today's local, regional, and global environmental challenges and to those uncertain environmental challenges that may surface in the future. Such a multipurpose strategy was unanimously endorsed in the regional reviews.
The essential message is that quality matters. The trend toward higher-quality, more flexible, and cleaner energy - an energy mix increasingly composed of electrons and hydrogen rather than carbon atoms - is strong. As in the past, progress will be gradual. The energy system changes slowly, and big, long-term shifts need to be prepared well in advance. The initiatives, incentives, and policies put into place over the next two decades will determine how quickly these efforts will bear fruit in the form of energy system decarbonization. From the perspective of both the global and regional analyses, a resilient strategy responds to consumer preferences and the need to preserve the environment both locally and globally.
The six scenarios illustrate the congruence of many energy-environmental policies. Efficiency improvements and changes toward cleaner energy conversion and end-use structures not only improve local and regional environments, but also mitigate against undesirable global changes. Consequently, they draw together the urgent local and regional environmental priorities of developing and transitional economies, and the concern about potential climate change evident in many industrialized countries and in countries particularly exposed to potential climate change risks.
But the scenarios also demonstrate that decarbonization is not enough to assure environmental compatibility - additional active policies will be required. At the regional level, active sulfur abatement strategies will be needed, particularly in the rapidly growing economies of Asia. Were sulfur emissions in the coal-intensive Scenario A2 left unabated, for example, ambient air quality in South and East Asia would deteriorate significantly in both metropolitan and rural areas reaching twice the worst levels ever observed in the most polluted areas of Central and Eastern Europe. For economically important food crops in Asia, Scenario A2's unabated emissions would cause critical loads to be exceeded by factors of up to 10 by 2020.
At the global level, carbon emissions vary substantially among the scenarios, and only the Case C scenarios describe a long-term emission path leading to stabilization of the atmospheric CO2 concentration below 450 parts per million by volume (ppmv). (Scenario A3 is consistent with stabilization below 550 ppmv if its emissions, which peak around 2060, continue to decline after 2100.) In the short-term, only Case C would be unambiguously in compliance with the emissions limits of the December 1997 Kyoto protocol to the UN Framework Convention on Climate Change (FCCC). As shown in Figure 5, none of the other scenarios is directly in compliance, but Case B and Scenario A3 come close.
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What makes compliance a possibility in Case B and Scenario A3 is that emissions decrease initially in FSU and EEU as a result of economic recessions in the early 1990s. In 2010 FSU emissions are below their Kyoto limits by about 120 megatons of carbon (MtC) in Scenario A3 and 280 MtC in Case B, a difference sometimes referred to as the ``Russian bubble.'' By itself the Russian bubble does not lead to compliance with the Kyoto Protocol. But with international emissions trading the bubble can go a long way in that direction, and Case B and Scenario A3 might therefore also comply with the Kyoto limits. Estimates of the potential trading price of emission reduction units range from US$10 per ton of carbon (tC) to US$200 per tC, making the total potential value of the Russian bubble huge and raising doubts about the practicality of implementing emission trading. Our analysis suggests that a particularly important potential candidate into which revenues from emission trading might be invested is a new gas transport infrastructure connecting the Siberian and Caspian regions with China and other rapidly developing countries in Asia. This would reduce long-term greenhouse gas emissions and air pollution in Asia and promote a cleaner environment in general.
The Kyoto Protocol is, however, only the first step in a long process. Accomplishing the emission reductions reflected in Case C would require that timely and tight limits be negotiated efficiently for commitment periods beyond 2008 to 2012, and that limitations are agreed to by all countries, North and South. Accomplishing stabilization along an alternative path, represented by Scenario A3, might also be possible, for example, if revenues from emissions trading under the Kyoto Protocol are invested prudently in post-fossil technologies and infrastructures. Explicitly dedicating revenues from emissions trading to such environmentally friendly purposes might also make both emissions trading and resource transfers more politically acceptable in the short term.