For many people, the most familiar way to “go green” or “be eco-friendly” is probably paper recycling. (And perhaps its aging office cousin: “Consider a tree before you print this email.”) There are many ways to evaluate the environmental benefits of such actions, and one of those is greenhouse gas emissions. So how does paper recycling stack up in this regard?

That’s a more interesting question than it may seem, namely because of the way paper products are made. Processing pulp to make paper is typically powered by “black liquor”—a byproduct organic sludge with some useful properties. Burning it for heat and electricity to run the mill is approximately carbon neutral, since the carbon you emit into the air started out in the air (before a temporary stint as tree stuff). So if your recycling process generates CO₂ as it makes new paper, recycling could end up increasing emissions.

A new study led by Stijn van Ewijk at Yale University tries to do the math on this, using practical scenarios for the next few decades. Namely, they calculate whether increasing paper recycling would make it easier or harder to hit emissions targets that would halt global warming at 2°C.

The researchers start by projecting growing global paper demand, driven especially by less-wealthy nations increasing their use of packaging. They then feed this into three scenarios applied to each step of the paper life cycle. One scenario continues current trends in things like energy mix and landfill management, while the other two represent more aggressive efforts to clean up electric grids and reduce emissions. These future scenarios, which go out to 2050, include a doubling in the share of paper that gets recycled.

Let’s start with 2012

For a baseline, they estimated global emissions associated with paper for 2012. This includes emissions from the energy used for harvesting wood, producing paper, manufacturing paper products, recycling paper, and disposing of paper in landfills (which can emit greenhouse gasses) or incineration plants. That finds that the paper life cycle actually accounted for about 1.2 percent of total global emissions in 2012.

A couple of simplifying assumptions are at work here. One is that the researchers simply use global averages for things like emission from the electric grid rather than trying to divvy up paper production locally. This is partly because they want to give a general answer about the effects of recycling. The other assumption is that the paper industry (recycling or no) doesn’t change the amount of carbon in forests. That may sound strange, but the idea is that this actually depends more on how the forestry is done. Harvesting trees for paper can be done sustainably or unsustainably. And reducing virgin material demand for paper may or may not actually translate to more carbon staying in forests depending on other drivers of deforestation. All those questions are set aside.

Paper air plan

The results show that, even with a moderately cleaner energy system in 2050, doubling the rate of recycling while increasing overall production would lead to slightly more emissions than the 2012 baseline. But with more aggressive improvements across the board, substantial emissions reductions would be possible.

Put another way, hitting targets consistent with that 2°C warming goal requires greater improvements to the energy supplying recycling activities and to landfill management. Otherwise, trading out virgin paper production (with its use of carbon-neutral fuels) for recycling plants running on fossil fuel energy leaves emissions treading water.

Breaking the results down by individual factors illustrates what’s going on. If nothing else changed from 2012, maxing out paper recycling would increase emissions for the paper industry. But cleaning up the grid (and/or reducing emissions from fuels burned for heat) has a large impact on the industry’s carbon footprint. Secondary to that, reducing emissions from paper that does end up in landfills—by capturing methane and burning it to generate electricity—would also have a significant impact.

So if your focus is solely on reducing greenhouse gas emissions, paper recycling isn’t the lever you pull. Instead, you target the factors surrounding paper recycling (and many other things). But given success on those things, increased paper recycling is perfectly consistent with global emissions targets. In the scenario with the most aggressive improvements, the researchers calculate that paper industry emissions could be slightly less than zero. That is, the growing amount of paper products in circulation would represent a bit more carbon than was released to make them.

Of course, paper recycling can have benefits separate from greenhouse gas emissions. Ideally, it helps reduce deforestation and habitat loss—which would also improve the bottom line for emissions. There are no sustainability silver bullets, but this study shows that paper recycling can at least fit in the puzzle.

Nature Sustainability, 2020. DOI: 10.1038/s41893-020-00624-z (About DOIs).