The BBC programme, broadcast in 2017, highlighted humanity’s impact on the oceans and the growing problem of plastic pollution.
It was credited with the “Blue Planet effect,” which saw people choosing to consume less plastic by opting for reusable items such as water bottles over single-use versions.
However, an experiment by Imperial College London and the University of Oxford suggests that although watching the documentary increased environmental awareness in a group of volunteers, it did not translate into choosing to use fewer single-use plastics.
First author Matilda Dunn, from the Centre for Environmental Policy at Imperial, said: "The findings from our experiment are counter to the popular idea that Blue Planet II reduced viewers' preference for plastic, instead demonstrating that human behaviors are complex and determined by more than just knowledge.
"However, 'Blue Planet II' may have had a wider impact by increasing conversations around ocean plastic pollution, allowing the topic to become more politically palatable."
The team split 150 people into two groups and asked them to complete questionnaire measuring their understanding of and attitudes towards marine conservation ideas.
One group was then shown the original The Blue Planet documentary, which was broadcast in 2001 and contained no plastic or ocean conservation messages, while the other was shown Blue Planet II. Both groups then filled out the same questionnaire.
Before and after both showings, the participants were offered a choice of drinks and snacks which were either in paper or plastic packaging. The researchers controlled for other differences between the options, such as flavours or sizes of the snacks, such as by offering the same soft drinks in both plastic and paper cups.
The study, published in published in Conservation Science and Practice, found that although watching Blue Planet II greatly increased the participants’ understanding of marine conservation ideas, there was no significant difference in the choices people made between plastic and paper-packaged snacks.
Co-author Dr. Morena Mills, from the Centre for Environmental Policy at Imperial, said: "Many previous studies of people's preference for plastic rely on individuals reporting their own preference, which can be unreliable. We are the first to use this type of experimental design along with measuring observed behaviors to test the hypothesis."
The researchers are planning to use their evaluation method to test the effectiveness of other conservation-related mass media interventions.