Subject(s): Economics and ecosystem, Climate change , Fossil fuels -- Reducing hunger : cropland trends, water, Food security trends -- Managing freshwater supplies : water cycle and renewable supplies, New water economy -- Maintaining world fisheries : fish farming, Salmon ranching -- Protecting forest from air pollution and acid rain -- Conserving biological diversity : Biotechnology and diversity -- Increasing energy efficiency -- Renewable energy , Hydrapower, Solar water heating, Solar thermal power generation , Alcohol fuels -- Stopping population growth -- one child families , Restoring environment