In the international community, people are particularly concerned about the plastic pollution crisis. The serious pollution of plastics can not be avoided. Many countries have issued prohibition policies on disposable plastic products that are not easy to recycle and easy to pollute, which also promotes the application of biodegradable materials. However, relatively speaking, the media and the public pay little attention to the impact of plastics on climate change. Why is the proliferation of plastics threatening the global climate? Can the "entry" of biodegradable plastics help combat climate change to some extent?
Atmospheric carbon dioxide concentration detected by monaloa Observatory from 1975 to 2018 (unit: ppm)
01 Exacerbate the climate crisis, the hidden cost of "plastic planet"
Coping with climate change is the most important issue in the world today. According to the special report on global warming of 1.5 ℃ issued by the United Nations Intergovernmental Panel on climate change (IPCC), the global warming range must be controlled within 1.5 ℃, otherwise the earth will usher in a devastating climate after 2030, when human society and ecosystem will be seriously affected.
In response, the international community reached the Paris Agreement on climate change in December 2015. The agreement sets an ambitious goal to control the global temperature rise within 2 ℃ compared with the pre industrial period within this century, and strive to control it within 1.5 ℃.
Plastic growth and emissions growth will exacerbate climate change
However, the greenhouse gas emissions of plastics in the whole life cycle are threatening the realization of our global climate goals:
1、 The combustion of fossil fuels releases a large amount of Co. To deal with climate change, the international community must quickly reduce the use of fossil fuels. However, almost all plastics come from fossil fuels.
2、 Plastic manufacturing is energy intensive and emission intensive. By cracking alkanes into olefins, polymerizing and plasticizing olefins into plastic resins, and other chemical refining processes, it will produce great greenhouse gas emissions, which is contrary to our global climate goal.
3、 Greenhouse gases are emitted at each stage of the life cycle of Plastics: 1) exploitation and transportation of fossil fuels, 2) refining and manufacturing of plastics, 3) management of plastic waste, and 4) the continuous impact of plastics into the marine, water and land environment. 
Emissions from plastics throughout their life cycle
According to the current trend, by 2050, the cumulative greenhouse gas emissions from plastics may exceed 56 billion tons, accounting for 10-13% of the total remaining carbon budget. As a greater threat lurking behind plastic waste, climate change is clear. 
It is not impossible to control the temperature rise within 1.5 ℃, but unprecedented action needs to be taken immediately on the greenhouse gas emission of plastics.
02 Biodegradable plastics are unlikely to achieve climate goals
In response to climate change, in 2020, China proposes to strive to achieve carbon peak by 2030 and carbon neutralization by 2060.
In the same year, in order to actively deal with plastic pollution, the national development and Reform Commission and the Ministry of ecological environment issued the opinions on Further Strengthening the treatment of plastic pollution, put forward a series of policies and measures to orderly prohibit and restrict the production, sales and use of some plastic products, and actively promote recyclable, recyclable and degradable alternative products. Biodegradable plastics have attracted much attention because of their compostable biochemical treatment.
According to the source of raw materials, biodegradable plastics can be divided into bio based biodegradable plastics and petrochemical based biodegradable plastics. It is generally believed that compared with ordinary plastics (i.e. petrochemical based non degradable plastics), the total amount of greenhouse gases emitted by bio based biodegradable plastics in the whole life cycle is usually low. In addition, in the waste management stage, compared with the incineration treatment of ordinary plastics, biodegradable plastics as composting biochemical treatment is conducive to greenhouse gas emission reduction .
However, there are also some pessimistic views on whether biodegradable plastics can help reduce the carbon footprint of plastics. Plants carry out photosynthesis and absorb CO in the whole life cycle, but the production of bio based biodegradable plastics consumes plants. At this level, bio based biodegradable plastics may not be conducive to reducing the plastic carbon footprint .
In the waste management stage, biodegradable plastics may affect the carbon sequestration of coastal ecosystems and impair their ability to mitigate climate change. It is found that biodegradable plastics may promote the metabolic pathway of seafloor anaerobic sediments and lead to the decomposition of marine buried organic carbon. Therefore, if biodegradable plastics replace ordinary plastics and become the main component of marine plastic pollution, it may affect the carbon sequestration of coastal ecosystems and damage their ability to mitigate climate change .
Biodegradable plastics may promote the decomposition of buried organic carbon in the ocean
We should also pay attention to the production of bio based plastics and the use of land. At present, the land use of bio based plastics in the world accounts for about 0.02% of the world's arable land. Assuming that plastic production is completely shifted to biomass resources, up to 5% of arable land will be required .
Based on the above, there are still doubts about how the use of biodegradable plastics will affect the global plastic carbon footprint. However, taking China as an example, it has been less than 10 years since the peak of carbon dioxide emissions will be achieved by 2030. Therefore, how to reduce the carbon footprint of plastics? This problem is particularly urgent.
03 "Four simultaneously" to reduce the carbon footprint of plastics
According to a study published in the journal nature climate change, the greenhouse gas emissions in the production stage of plastic resin account for 61% of the emissions in the whole life cycle, 30% in the plastic processing stage and 9% in the plastic waste management stage. On this basis, the study assessed the potential of four measures to reduce greenhouse gas emissions from plastics:
1) Demand management (i.e. reducing production of plastics)
2) Energy decarbonization (replacing fossil energy with renewable energy)
4) Bio based plastics (i.e. using biomass resources)
The study shows that bio based plastics produce lower greenhouse gas emissions than petrochemical based plastics in the whole life cycle. However, compared with using biomass resources to produce plastics in the production stage, recycling plastics in the waste management stage can bring lower greenhouse gas emissions, that is, using recycled plastics will produce less greenhouse gases than using native biomass plastics .
The study found that the greenhouse gas emissions in the global plastic life cycle can be minimized by 100% bio based plastics, 100% energy decarbonization, 100% recycling and reduced demand growth. Based on the global greenhouse gas emissions of plastics by 2050, compared with the current trend, the adoption of this combination of measures (demand growth reduction assumes that the annual growth rate of global plastic demand drops to 2%) is expected to reduce emissions by 93% .
The four measures need to be coordinated. If any of them is taken alone, it will not achieve the much-needed greenhouse gas emission reduction. This shows that it is technically possible to significantly reduce greenhouse gas emissions in the global plastic life cycle, but it needs to promote the implementation of all four measures on an unprecedented scale and speed.
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