CEE April-June 2012

meet societal needs and be compatible with social norms now and in the future. Indeed, as use of RE technologies accelerates, a balance will have to be struck among the several dimensions of sustainable development. It is important to assess the entire lifecycle of each energy source to ensure that all dimensions of sustainability are met. Options for mitigation There are multiple means for lowering GHG emissions form the energy system while still providing energy services. Many options and combinations are possible for reducing emissions. The Assessment Report 2007, identified a number of ways to lower heat trapping emissions from energy sources while still providing energy services. They include: • Improve supply side efficiency of energy conversion, transmission and distribution including combined heat and power; • Improve demand side efficiency in the respective sectors and applications (e.g., buildings, industrial and agricultural processes, transportation, heating, cooling, lighting etc.); "This Report of the IPCC focuses on substitution of fossil fuels with low carbon RE to reduce GHGs, and examines the competition between RE and other options to address global climate change." • Shift from high GHG energy carriers such as coal and oil to lower GHG energy carries such as natural gas, nuclear fuels and RE sources; • Utilize carbon capture and storage (CCS) to prevent post combustion or industrial process C02 from entering the atmosphere. CCS has the potential for removing C02 from the atmosphere when biomass is burned; and Wi nd rurbine~ x Change behaviour to better manage energy use or to use fewer carbon and energy intensive goods and services. Two additional means of reducing GHGs include enhancing the capacity of forests, soils and grassland sinks to absorb C02 from the atmosphere and reducing the release of black carbon aerosols and particulates from diesel engines, biomass fuels and from the burning of agricultural fields. Additional reductions in non C02 heat trapping GHGs (CH 4 , N20 , hydro fluorocarbons, sulphur hexafluoride) can also reduce global warming. Gee-engineering solutions have been proposed to address other aspects of climate change, including altering the heat balance of the Earth by increasing surface albedo (reflectivity), or by reflecting incoming solar radiation with high altitude mirrors or with atmospheri c aerosols. Enhanced C02 absorption from the atmosphere through ocean fertilization with iron has also been proposed and tested. A comprehensive evaluation of any portfolio of mitigation option would involve an evaluation of their respective mitigation potential as well as all associated risks, costs and their contribution to sustainable development. This Report of the IPCC focuses on substitution of fossil fuels with low carbon RE to reduce GHGs, and examines the competition between RE and other options to address global climate change. Setting a climate protection goal in terms of the admissible change in global mean temperature broadly defines (depending on the assumed climate sensitivity) a corresponding atmospheric C0 2 concentration limit and an associated carbon budget over the long term. This budget, in turn, can be broadly translated into a time dependent emission trajectory that serves as an upper bound or (if the remaining time flexibility is taken into account) in an associated corridor of admissible em1ss1ons. Subtracting any expected C02 emissions from land use change and land cover change constrains the admissible C0 2 emissions that could be realized by freely emitting carbon fuels (i.e., coal, oil, and gas burned without applying carbon capture technologies), The corresponding fossil fuel supply is part of the total primary energy supply (TPES) is provided by zero or low carbon energy technologies, such as RE, nuclear or the combustion of fossil fuels combined with carbon capture and storage (CCS). Whereas the admissible amount of freely emitting fossil fuels in mainly fixed by the climate protection goal , the complementary contribution of zero or low carbon energies to the primary 38