|Above: Plastic bottle caps are seen in the courtyard of a MP Industries waste recycling plant in Gardanne, near Marseille, France, on November 23, 2018, during the launch of a zero plastic waste campaign in the European Week for Waste Reduction. Image credit: Gerard Julien/AFP/Getty Images.|
A new paper in Nature Climate Change—just in time for Earth Day—provides the first global, end-to-end analysis of the carbon footprint of plastics, and goes on to take a close look at four ways we can reduce that footprint.
While they did find multiple rays of hope, Jiajia Zheng and Sangwon Suh (University of California, Santa Barbara, or UCSB) also found that no single approach will do the trick: “Our study shows that an aggressive implementation of multi-layered strategies would be needed in order to curb the GHG [greenhouse gas] emissions from plastics.”
Global plastics production has increased at a breakneck pace, from 2 million metric tons in 1950 to 70 million by 1980 and 381 million by 2015, according to a 2017 analysis in Science Advances led by UCSB’s Roland Geyer. Since plastics are growing more rapidly than total greenhouse emissions, “business as usual” means an ever-growing share of the global greenhouse burden will come from plastics.
The drive to eliminate single-use plastics (the items we use once and then toss) has gained considerable momentum since the last Earth Day. At least 32 countries and 2 states (California and Hawaii) have banned plastic bags, and some 200 U.S. cities now either ban plastic bags or require consumers to pay a fee to get one. Straws and other single-use food items are the next rampart being stormed. The European Union has voted to ban all single-use plastics—including plates, knives, spoons, forks, chopsticks, straws, and polystyrene cups—by 2021. Many companies are following suit in one form or fashion.
Such moves are largely driven by the long lifetime of typical plastic trash (hundreds to thousands of years before biodegrading) and the horrific effects of plastic fragments on at least 800 species of aquatic life. One study found that some 5 trillion bits of plastic are floating in the world’s oceans. What’s gotten much less attention is the greenhouse impact of making plastic, in part because it’s rarely been quantified.
|Figure 1. A woman collecting plastic to be recycled from a import plastic waste dump on December 4, 2018 in Mojokerto, East Java, Indonesia. The U.S. is one of the largest exporters of plastic to be recycled elsewhere, shipping more than half a million metric tons overseas in the first half of 2018, as reported by the Guardian. Image credit: Ulet Ifansasti/Getty Images.|
According to the analysis of Zheng and Suh, the full life cycle of plastics—from manufacture to disposal—accounted for 3.8% of global greenhouse gas emissions in 2015, expressed as carbon dioxide equivalent. That percentage drops to 3.5% when the benefits of recycling in reducing new plastics are taken into account.
More than half (61%) of the emissions arose early on, from using hydrocarbons (usually from fossil fuels) as “feedstocks” to make polymer resins. The heating and shaping of resins into various types of plastics accounted for 30% of the emissions. “End-of-life” processes (landfills, recycling, and especially incineration) led to the remaining 9%.
The four pathways and how they might intersect
Zheng and Suh looked at four main scenarios in isolation, each relying on a known approach that could reduce emissions from plastic production.
—Bio-based plastics. About 0.6% of the world’s plastics in 2017 were made using bio-based rather than fossil-fuel-based feedstocks. Zheng and Suh modeled a gradual transition toward 100% corn or sugarcane feedstocks (currently the most common bio-based alternatives) by 2050.
—Renewable energy. This scenario replaces the current energy mix in plastics production with a fully renewable mix (wind power and biogas) by 2050.
—Recycling. The current rates of recycling are assumed to reach 100% by 2050.
—Demand growth. The average growth rate of 4%/year in plastics demand that prevailed from 2010 to 2015 is decreased to 2% through 2050.
Together, these approaches could in theory eliminate more than 90% of the plastics-based greenhouse emissions we'd otherwise have by 2050. “We examine these strategies as illustrative scenarios, rather than as realistic projections of future trajectories, with the purpose of envisioning their potentials for GHG mitigation," Zheng and Suh emphasize. "We acknowledge that achieving 100% recycling or renewable energy may be neither practical nor economically feasible in reality.”
By itself, switching completely to corn- or sugarcane-based feedstocks would only trim about 15% or 25%, respectively, from plastics-related emissions by 2050. That’s because a much larger contributor than feedstock to plastics’ greenhouse burden is the energy used in manufacturing. A full-on switch to bio-based feedstocks would also have major side effects, perhaps gobbling up as much as 5% of the world’s arable land.
In contrast, switching to all-renewable energy would cut more than half (51%) of the total greenhouse emissions from plastic production. Similarly, reducing the demand growth by half would by itself (not surprisingly) cut 2050 emissions by half.
Cutting the expected 2050 emissions in half, though, would still mean roughly twice as big a carbon footprint from plastics in 2050 as in 2015, because plastics-related emissions are now set to quadruple on a business-as-usual path. There’s no way to get to zero or negative emissions growth from plastic, according to Zheng and Suh, unless more than one approach is used: “This result shows that absolute reduction of emissions can only be achieved by combining aggressive deployment of renewable energy and extensive recycling of plastics.”
There’s certainly room to expand the use of renewable energy in plastics manufacturing—in polymer processing, for example. Recycling is also far from ubiquitous. Globally, only about 18% of plastic was being recycled as of 2015, according to Geyer and colleagues.
Making it easier for consumers to recycle is one obvious piece of the puzzle. There’s also some hope for making recycling itself more effective, especially given that it’s hard to avoid some level of contamination (bits of food, for example) that can muck up the recycling stream. For instance, IBM has developed a technology called VolCat that can latch onto the polyesters in PET (polyethylene terephthalate)—one of the most commonly recycled plastics—and, using a special catalyst, produce the main ingredient of virgin-quality PET without any interference from contaminants. For more about VolCat, see the brief animation below and the interactive feature posted by IBM Research.
A tough year for recycling
Meanwhile, the recycling industry itself is under unprecedented stress. In early 2018, China—the world’s leading processor of recycled waste—banned the import of solid waste, throwing a wrench into nearly half the world’s recycling and triggering a cascade of consequences upstream. “Is This The End of Recycling?” asked the Atlantic last month. The website Waste Dive has a detailed state-by-state guide, updated daily, to the adaptations and complications that are still unfolding.
As for reducing demand for plastic, much of that comes down to you and me. I’ve got a portable stainless-steel water jug and a coffee/tea tumbler that I use daily. Together, they’ve saved me from using many hundreds of plastic cups and water bottles, plus kept my beverages satisfyingly hot or cold for much longer then the plastic ever could have. When running errands, I’ve got several washable bags that over the years have carried several tons of groceries, without once splitting in half in the parking lot.
Plastics manufacturers point out that plastics actually have a place in helping to cut emissions. They’re used in automobiles, aircraft, wind turbines, and many other places to help reduce weight and friction and improve efficiency. It’s a fair point—and all the more reason to skip plastic where we really don’t need to use it.
Happy Earth Day!