As useful as it may be, plastic has become a household-synonym for "environmental pollution": It is based on fossil fuels and releases large amounts of CO₂ when broken down, thereby contributing significantly to global warming. Biobased plastics - or bioplastics for short - are often advertised as a sustainable alternative with a neutral carbon footprint. Researchers in Bonn have  analysed the underlying manufacturing processes and materials and warn that the increased production of bioplastics could have in fact negative consequences regarding climate change. They published their results in the journal "Environmental Research Letters".

Forests are turned into fields and release massive quantities of CO₂

According to Neus Escobar of the Institute of Food and Resource Economics at the University of Bonn, the production of large quantities of bioplastics would change land use globally. "This could potentially lead to an increase in the conversion of forest areas to arable land. However, forests absorb considerably more CO₂ than maize or sugar cane annually, if only because of their larger biomass," said the researcher. Escobar and her colleagues simulated the possible consequences by using an extended computer model. The model is based on a database that maps the entire world economy and has previously been used to investigate the relationship between the increasing demand for biofuel and deforestation.

Tax conventional plastics or subsidize bioplastics?

For their calculations, the Bonn-based researchers assumed that the amount of bioplastics produced by the most important economies - Europe, China, Brazil and the USA - will increase to five percent. In order to analyse the effects on the market and the environment, they used the computer model to simulate two different scenarios: Either conventional plastics were taxed and thus more expensive, or bioplastics were subsidised and thus cheaper. The effects for the tax scenario were most striking: Due to the decreasing demand for conventional plastics, 0.08% less greenhouse gases were emitted per year. At the same time, the agricultural area increased, while the forest area decreased by 0.17%. Plus, the conversion of forest to arable land released enormous quantities of greenhouse gases into the atmosphere. Although, according to the researchers, this would be a one-off effect, "Nevertheless, according to our calculations, it will take more than 20 years for it to be offset by the savings achieved by fossil substitution," Escobar explains. A subsidy for bioplastics in turn would have very similar consequences with regard to the 20-year compensation period.

Bioplastics made from plant waste are the only truly sustainable alternative

The researchers' conclusion: "Consuming bioplastics from food crops in greater amounts does not seem to be an efficient strategy to protect the climate". If, on the other hand, bioplastics were produced from plant waste or crop residues, the carbon footprint would be much more positive. Escobar and her colleagues therefore recommend research projects to focus on "second generation bioplastics".

In addition they highlight that bioplastics do not solve the "plastic waste problem" because bioplastics are often just as difficult to degrade as their petroleum-based counterparts. However, bioplastics and biomaterials have one clear advantage: they help to reduce the fossil fuel dependency. Nonetheless, in order to protect the environment, the scientists recommend that plastics in general be used sparingly and recycled as much as possible.

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