Environmental aspects 27 Economic aspects 14 Sustainable development 14 Government policy 12 Environmental policy 10 Conservation of natural resources 7 Energy policy 7 Mais ... International cooperation 6 Women 6 Birth control 5 Effect of human beings on 5 Food supply 5 Nature 5 Pollution 5 Recycling (Waste, etc.) 5 Social aspects 5 Energy conservation 4 Natural resources 4 Population 4 Population policy 4 Solar energy 4 Climatic changes 3 Disarmament 3 Economic policy 3 Environmental protection 3 Forest conservation 3 Forests and forestry 3 Freshwater ecology 3 Health aspects 3 Law and legislation 3 menos ...