For many people, recycling paper is probably the best-known way to “go green” or “be environmentally friendly”. (And maybe his aging cousin in the office: "Look at a tree before you print this email.") There are many ways to assess the environmental benefits of doing so, and one of them is greenhouse gas emissions. How does paper recycling stack up in this regard?
This is a more interesting question than it may seem because of the way paper products are made. The processing of pulp to make paper is typically powered by "black liquor" – an organic by-product sludge with some beneficial properties. Burning for heat and electricity to run the mill is roughly climate neutral as the carbon you give off into the air started in the air (prior to a temporary stay as building material). If your recycling process generates CO2 when making new paper, recycling can increase emissions.
A new study led by Stijn van Ewijk from Yale University tries to calculate this using practical scenarios for the next few decades. Namely, they calculate whether increasing paper recycling would make it easier or more difficult to meet emission targets that would stop global warming at 2 ° C.
The researchers initially forecast a growing global demand for paper, which will be driven in particular by less affluent countries that are increasingly using packaging. You then feed this into three scenarios that are applied to each step of the paper lifecycle. One scenario continues current trends in terms of energy mix and landfill management, while the other two represent more aggressive efforts to rehabilitate power grids and reduce emissions. These future scenarios, which assume until 2050, include a doubling of the proportion of paper that is recycled.
Let's start with 2012
As a basis, they estimated the global emissions associated with paper for 2012. This includes emissions from the energy used for wood harvesting, the manufacture of paper, the manufacture of paper products, the recycling of paper and the disposal of paper in landfills (the greenhouse gases can emit) or the combustion is used plants. This shows that the paper life cycle actually accounted for around 1.2 percent of total global emissions in 2012.
Some simplifying assumptions are at work here. For one thing, the researchers are simply using global averages for things like emissions from the power grid, rather than trying to break down paper production locally. This is partly because they want to give a general answer on the impact of recycling. The other assumption is that the paper industry (recycle or no) does not change the amount of carbon in forests. That may sound strange, but the idea is that it actually depends more on how the forestry is done. Harvesting trees for paper can be sustainable or unsustainable. And reducing the need for virgin paper can result in more carbon remaining in forests, depending on other drivers of deforestation. All of these questions are set aside.
Enlarge /. Here is the level of recycling in 2012 compared to the rate envisaged in the future scenario.
Paper flight plan
The results show that even with a moderately clean energy system, doubling the recycling rate in 2050 while increasing overall production would lead to slightly more emissions than in 2012. However, with more aggressive improvements across the board, significant emissions reductions would be possible.
In other words, in order to achieve targets that are compatible with this warming target of 2 ° C, recycling activities for energy supply and landfill management must be improved more. Otherwise, trading in the production of fresh paper (using climate-neutral fuels) for recycling plants that run on energy from fossil fuels will result in emissions entering the water.
Enlarge /. Calculated emissions for the paper industry in 2012 and the three scenarios for 2050, which contain different improvements related to things like our energy mix.
The breakdown of the results by each factor shows what is going on. Unless otherwise changed from 2012 onwards, maximizing paper recycling would increase emissions for the paper industry. However, cleaning up the power grid (and / or reducing emissions from fuels burned for heat) has a huge impact on the industry's carbon footprint. Second, reducing emissions from landfill paper – by capturing methane and burning it to generate electricity – would have a significant impact.
So if you are solely focused on reducing greenhouse gas emissions, paper recycling is not the lever you are pulling. Instead, you target the factors that affect paper recycling (and many other things). In view of these successes, however, increased paper recycling is perfectly in line with global emissions targets. In the scenario with the most aggressive improvements, the researchers calculate that emissions from the paper industry could be slightly below zero. This means that the increasing amount of paper products in circulation would represent a little more carbon than was released during manufacture.
Of course, paper recycling can have benefits that are separate from greenhouse gas emissions. Ideally, it will help reduce deforestation and habitat loss – which would also improve the bottom line for emissions. There are no silver bullets for sustainability, but this study shows that paper recycling can at least fit into the puzzle.
Nature Sustainability, 2020. DOI: 10.1038 / s41893-020-00624-z (About DOIs).