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These complex , interacting dimensions of vulnerability to environmental change can act either as the constituent elements of vulnerability or , depending on the coping capacities ( see Box 3.5 ) and resilience of an affected population , can result from , or be exacerbated by , environmental change . The Johannesburg Plan of Implementation , agreed at the World Summit on Sustainable Development in 2002 , includes commitments to diversify energy supply and to increase substantially the global share of renewable energy sources ; to improve access to reliable , affordable , economically viable , socially acceptable and environmentally sound energy services and resources ; and to establish domestic programmes for energy efficiency , among other things . In turn , African governments , AMCEN and the sub-regional organizations may enter into partnerships with sub-regional , national and international organizations , to further facilitate implementation . Commercial applications of solar thermal electric technologies which could generate in the range of a few kilowatts to hundreds of megawatts are technically feasible though not yet economically competitive . Consequently , there is absolute need to strengthen policy implementation measures at community , national , sub-regional and regional levels . In addition to the regional and sub-regional initiatives mentioned above , there have also been country level efforts , a summary of which is presented in Annex 1 . The size and shape of a city ; meteorological and climate conditions ( for instance , temperature , wind speed and the existence of thermal inversions ) ; number of inhabitants per square kilometre ( hence emission density ) ; and the seasonal distribution of the emissions are also important . Indoor air pollution requires viable , costeffective interventions that can reduce exposures and improve health . Information on thermal characteristics is also valuable for prospective homeowners – buyers can make better decisions if they know the energy efficiency of the house they are thinking of buying . Where the geographical location is suitable , solar thermal technologies such as solar cookers and water heaters are available for residential uses . Implementation of the recommended actions is principally the responsibility of African governments , with technical assistance from AMCEN and sub-regional organizations . Historic and social-cultural reasons often explain the differences – and often also determine factors such as the early creation of an underground transport system , or bicycle lanes to encourage more sustainable forms of transport . African countries are party to various policy instruments at global , regional , sub-regional and national levels .