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If we were to make some technical jump to renewable fuel and renewable energy, would making plastics from oil release green house gasses, how much, and would plastic function as a carbon sink?

Sorry if this is a basic question I don’t know much about earth science.

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    $\begingroup$ The crude oil from which most plastic is made is a hydrocarbon & is already a carbon sink. Transforming oil into plastic would create another form of a carbon sink, but would also produce a lot of pollution & green house gases. The best solution would be to leave crude oil where it is in the ground. $\endgroup$
    – Fred
    Nov 29, 2018 at 17:50
  • $\begingroup$ It's really impossible to say for sure without knowing what plastics, and what chemical processes are used to create them. But unless the process involves adding extra C or CO2 to the oil, then at best it would be neutral. Realistically it would be less than neutral, because 1) Only a fraction of the crude oil becomes plastic, so what happens to the rest? 2) The plastics will almost certainly degrade. Even if it takes centuries, that's far less than the hundreds of millions of years that crude oil can stay in the ground. $\endgroup$
    – jamesqf
    Nov 30, 2018 at 19:20

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The idea of a carbon sink is a bit misunderstood here. The idea of a carbon sink is a reduction of carbon that comes from the atmosphere. It must “fix” carbon that is already in the air. Trees are a carbon sink, for the most part, because their mass is made of of carbon obtained from The atmosphere. Unless the plastic formation process you are thinking of is vastly different that any industrialized ones, they are taking carbon from oil essentially. Since the carbon from the oil Has not yet been released into the atmosphere, it would not qualify as a sink.

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Most plastics are made from the already-sunk carbon of crude oil or natural gas, and as a result, can be at best carbon neutral. However, bioplastics such as cellulose acetate or polylactic acid are derived from plant sources; the carbon here comes from the atmosphere, and they can theoretically act as carbon sinks.

However, even if we switched all our plastic use to bioplastic, and disposed of it in ways that kept it from decomposing, there's not enough of it to be a useful carbon sink. There are about 1000 billion tons of carbon dioxide in the air above prehistoric levels; humans have produced only about 8 billion tons of plastic in the past century.

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    $\begingroup$ I wouldn't be so defeatist. Each year we produce 0.3 billion tonnes. If we try hard, we can scale that up significantly. If we encourage consumption of single-use plastics derived from plant sources then it becomes economically self-sustaining. We could pull 1 billion tonnes out of the atmosphere each year. And there's more carbon per mole in plastic than in CO2, right, so the 1000 vs 8 billion is apples-vs-oranges. $\endgroup$
    – Tim Cooper
    Jan 28, 2020 at 6:52
  • $\begingroup$ @TimCooper, PLA and cellulose acetate are both about 50% carbon by weight. Carbon dioxide is about 27% carbon by weight. It's not an apples-to-apples comparison, but it's not too far off. (And deliberate inefficiency won't help either practically -- most plastics are single-use -- or economically -- see Broken window fallacy.) $\endgroup$
    – Mark
    Jan 28, 2020 at 20:56
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Plastic is a much less efficient carbon sink than the original crude oil if it had been left in the ground or any natural method for storing carbon such as peat bogs. It is still technically a carbon sink but is starting to be broken down naturally so is not a renewable or sustainable one. Pollution and green house gasses are a major part of plastic production so environmentally it does not make sense to produce plastics a carbon sink unless you were converting biodegradable plastic into non biogradeable plastic without releasing any harmful gasses in the process. Hope this helps.

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