At face value, taxing consumption of materials derived from petrochemicals and subsidizing production of bioplastics both sound like they’d encourage sustainable consumption. But applying these policies to meet a hypothetical 5% target for bioplastics use reveals a different story, according to scientists in Germany.

Today, bioplastics have a market share of around 1%, but as this number rises so does the amount of sugar- and starch-based feedstock that must be grown.

The researchers found that land use changes to provide this feedstock — particularly, the conversion of managed forests into cropland, eliminating valuable carbon sinks — lead to an overall rise in greenhouse gas emissions.

Both taxes and subsidies help suppress the market for petroleum-derived plastics (by 0.37% and 0.07%, respectively). But subsidies increase competition for land, displacing other uses, and taxes risk economic penalties.

Calculations based on the tax scenario reveal a subsequent contraction of all sectors employing plastics, equivalent to an annual drop of 0.07% in global real GDP.

Read more at Physics World