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There's a relatively new word doing the rounds in sustainability research: defossilization. Beyond expert circles, it isn't necessarily obvious that eliminating fossil (化石) fuels does not mean phasing out carbon.

Defossilization means finding sustainable ways to make carbon-based chemicals. This carbon cannot come from the usual sources, such as coal, natural gas and oil. Alternative sources of carbon include the atmosphere and plants, as well as carbon in existing biological or industrial waste, such as used plastics or agricultural waste. In some cases, these chemicals will eventually return CO₂ to the atmosphere through burning or biodegradation. In principle, this will occur as part of a circular process, rather than one that has added greenhouse gases.

The extraction (提取) of carbon from tough plant matter in crop waste is an alternative with potential that remains mostly unused. One major advantage is the fact that it can be produced without the use of extra land. But it is expensive to extract, and production timelines are long, both of which prevent its large-scale application.

Other potential sources of waste carbon include city and industrial waste, with used plastic among this. Current recycling methods break waste plastics into small pieces through melting, and then form small balls that can be used to make new products. For higher recycling rates to be achieved, chemical recycling methods will need to be further developed and scaled up.

CO₂ captured from the air offers one of the largest potential channels for defossilization. The global chemicals industry could obtain one-third of its carbon needs from this source by 2050. Although the atmosphere holds nearly 900 billion tons of carbon (almost twice the amount in vegetation), estimates of CO₂'s future contribution vary widely. Some say CO₂ will become the main material for chemicals, whereas others say its contribution will be insignificant.

To make useful carbon-based molecules (分子), CO₂ must first be transformed into other molecules. This requires a considerable amount of renewable energy because CO₂ is highly stable. Capturing atmospheric CO₂ is difficult and expensive, so some countries have not prioritized the technology-but this must change and needs a renewed focus on defossilization.