While it’s usually seen as a good practice, recycling paper is actually meaningful to the climate only when it’s powered by renewable energy, according to a modeling study. Greenhouse gas emissions would increase by 2050 if we recycle more paper, as current recycling methods rely on fossil fuels, researchers found.

A circular economy is expected to achieve sustainability goals through efficient use and reuse of materials. Waste recycling is an important part of a circular economy. However, for some materials, the potential environmental benefits of recycling are unclear or contested, say researchers from University College London.

Senior author Professor Paul Ekins said: “The recycling of some materials, for instance, metals, can lead to a very large reduction in emissions. But we need to be careful about assumptions that recycling, or a circular economy in general, will always have a positive effect on climate change.”

Lead author Dr. Stijn van Ewijk and his team modeled several scenarios for increasing recycling of wastepaper by 2050 and the impact this would have on greenhouse emissions. They found that if all wastepaper was recycled, emissions could increase by 10%, as recycling paper relies more on fossil fuels than making new paper.

Nevertheless, this doesn’t have to be the case. The researchers found that emissions would be radically reduced if paper production and disposal were carried out using renewable energy sources rather than fossil fuels. Renewables have never been cheaper, with solar expected to take over as the main energy source soon.

Making new paper from trees uses more energy than recycling it. But the energy for this process is generated from black liquor, the low-carbon by-product of the wood pulping process. In contrast, paper recycling relies on fuels and electricity from the grid. That’s the main concern of researchers, leading to emissions.

The team found that modernizing landfill practices can have a positive effect, such as capturing methane emissions and using them for energy. Nevertheless, the effect isn’t as significant as moving to renewables, they argued. For van Ewijk, recycling isn’t helpful unless it’s powered by clean energy sources.

“We looked at global averages, but trends may vary considerably in different parts of the world. Our message isn’t to stop recycling, but to point out the risk of investing in recycling at the expense of decarbonizing the energy supply and seeing very little change to emissions as a result,” he said

Paper accounted for 1.3% of global greenhouse gas emissions in 2012. About a third of these emissions came from the disposal of paper in landfills. The researchers argued that the use of paper will rise in the coming years, especially as the world moves away from plastics and instead uses paper packaging.

The researchers looked at how different levels of recycling, renewable energy use, and more environmentally friendly landfill practices affect our ability to reduce emissions. Counties agreed in the Paris Agreement to avoid global warming of more than 2ºC degrees compared to pre-industrial levels.

If past trends continue, emissions would slightly increase from the 2012 level (721 metric tons of carbon dioxide equivalent in a year) to 736 metric tons in 2050, the findings showed. A recycling program, with landfill and energy uses remaining on the same path, would increase this still further by 10% (to 808 metric tonnes).

On the other hand, the researchers argue, improving landfill practices would reduce emissions to 591 metric tons. Meanwhile, moving to renewable energy, with recycling and landfill practices remaining on the standard path, would reduce emissions by 96% to 28 tons, the study showed.

While paper recycling can save trees and protect forest carbon stocks, the extent of this effect is unknown, the researchers said. This is because of a lack of understanding of the global forest carbon stock and the interrelated causes of deforestation. The study, therefore, assumes that recycling neither harms nor benefits forests.

The study was published in the journal Nature Sustainability.