Development of new indicators for improved climate characterization of bioplastics: going beyond tipping the Arctic summer sea-ice

Bioplastics are often considered as environmentally sustainable solutions to mitigate climate change. Climate performance of bioplastics is traditionally assessed using Global Warming Potential (GWP) as indicator. Although credits can be given for temporary carbon storage in biomaterial, GWP does not consider the contribution of greenhouse gas (GHG) emissions to crossing of climatic tipping points, that is, levels of pressure on the climate system beyond which adverse and potentially irreversible changes may occur. Accounting for timing of GHG emissions is particularly relevant for some biodegradable materials made from biopolymers, which can degrade relatively quickly in the environment. Here, building on
recently developed Climate Tipping Potential (CTP) indicator, which quantifies impacts in relation to tipping the Arctic summer sea ice, a new indicator is proposed, which: (i) includes melting of Greenland icesheet as tipping element, and (ii) includes the contribution of tipping the Arctic summer sea ice to melting of the Greenland ice-sheet due to albedo changes. The new indicator was applied in practice to temporarily disaggregated CO2 emission inventories representing a wide range of bioplastics mineralization rate constants. For biodegradable bioplastics, it was found that total climate tipping impact caused by temporal evolution of CO2 from mineralization of bioplastic is dominated by contribution of CO
2 emissions to tipping the Arctic summer sea ice rather than tipping the Greenland ice-sheet. The latter may become important, however, for those bioplastics that degrade relatively slowly in the environment. These findings highlight the need
for considering timing of emissions as determined by biodegradability of the biopolymer in the environment, when characterizing climate-tipping performance of bioplastics.