Roger Spranz

• How can plastic bag use in Indonesia be reduced? This dissertation attempts to answer this question applying two approaches: (1) Utilizing qualitative and quantitative research to investigate crucial factors explaining plastic bag use; (2) Conducting natural field experiments to identify effective behavioral interventions reducing the use of plastic bags in Indonesia. The pollution of the oceans by plastic waste is a growing threat to marine life, ecosystems, livelihoods of coastal communities and the health of human beings in general. Indonesia is the world’s second largest source of marine plastic pollution. Regulations and policies have shown to be effective in the reduction of the use of and pollution by plastic bags in a number of countries. But for the Indonesian Government and many other governments the feasibility of implementing and enforcing such measures is limited. Given this situation, there is an urgent need to investigate and find effective alternative approaches to reduce plastic bag use. Such alternative approaches include non-governmental organizations, environmental groups and social enterprises. This research aims to explain plastic bag use with the help of research methods from cultural anthropology. Qualitative and quantitative methods were applied along with different types of triangulation to examine people’s concepts of nature, the perceived benefits and disadvantages of plastic bag use, and promising local initiatives. To find effective behavioral interventions for reducing plastic bag use we conducted natural field experiments. These tested normative and economic interventions in combination with ecofriendly reusable shopping bags. Specific interventions ranged from social norms and different societal authorities to indirect monetary incentives and bonus schemes. In this context we also analyzed socio-economic factors and environmental awareness in relation to frequency of plastic bag use.