Wednesday, March 05, 2025

Tree planting is still the best way to remove carbon – despite climate and economic risks

Uncertainty over climate and economy means ‘investment portfolio’ approach to tree planted needed

News Release 4-Mar-2025

University of ExetFacebook

Tree planting can be the most cost-effective way of removing carbon as long as careful choices are made about which type of trees to plant and where, a new study finds.

Governments worldwide have committed to expand tree cover to remove greenhouse gases, with the UK committing to plant 30,000 hectares of trees each year until 2050.

However, environmental economists point out that there are significant risks of converting farmland to forests comes in a future of climate change and economic uncertainty.

These include the risk of large-scale tree planting displacing agriculture and impacting food security, depending on where it takes place.

In a study in PNAS, the researchers use the UK as an example to demonstrate that uncertainties about climate change and the economy make the difficult trade-off between carbon removal and agriculture even tricker.

Frankie Cho, a PhD graduate from the University of Exeter and lead author of the study, explains: “One problem is that, because it is unclear what countries round the world will do to tackle climate change – we don’t know how challenging the climate will be in the future. If climate change is extreme, broadleaf trees in southern UK offer the best carbon removal – but that’s prime farmland and could be really costly under certain economic futures.

“If climate change is milder, planting conifers on less productive land makes more sense, but those trees will not grow well if conditions are more extreme. The problem is that we don’t know what the future holds and can’t be certain which type of trees we need to plant and where.”

However, using recent advances in decision-making theory under uncertainty, the researchers show that despite these risks, tree planting can still be the most cost-effective way to remove carbon.

Their study shows that a ‘portfolio’ approach to tree planting – diversifying species and planting locations - helps balances risks and moves beyond planting strategies that simply hope that everything will be ok.

This strategy minimizes the danger of betting on the wrong future, ensuring tree-planting decisions remain resilient in the face of uncertain future climatic and economic conditions.

Importantly, they show that if policymakers adopt these portfolio approaches to tree-planting, it becomes a far more cost-effective strategy for carbon removal than alternatives like biomass energy with carbon capture and storage or direct air capture technologies.

Co-author of the study, Professor Brett Day at the University of Exeter, added, “We don’t have any other option that can remove carbon from the atmosphere at the scale and cost that we need to meet our Net Zero targets. While tree-planting carries risks, our study shows that, if done strategically, it remains the best solution we have.”

“Resilient tree-planting strategies for carbon dioxide removal under compounding climate and economic uncertainties” is published in Proceedings of the National Academy of Sciences.

Journal

Proceedings of the National Academy of Sciences

TWO

10.1073/pnas.2320961122

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Resilient tree-planting strategies for carbon dioxide removal under compounding climate and economic uncertainties

Converting CO2 into fuel – with the help of battery waste

Upcycling as a climate game-changer: A nanocatalyst has been produced at TU Wien based on spent batteries and aluminium foil residues, converting CO2 into valuable methane.

Vienna University of Technology

Team — image:
Michael Stöger-Pollach, Hamilton Uchenna Aharanwa, Qaisar Maqbool, Günther Rupprechter (left to right)
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Credit: TU Wien

Battery waste is a serious environmental problem: it contains substances that pose a threat to both human health and ecosystems. At the same time, however, they also contain valuable materials such as nickel, which we need – for example, for the production of new batteries. Better recycling methods for batteries are therefore urgently required.

At TU Wien, it has now been possible to develop a process that can be used to recover nickel from spent nickel-metal hydride batteries. But that's not all: from this battery waste and used aluminium foil, such as that used in the kitchen, it was possible to produce a nanocatalyst that converts CO2 into valuable methane. In this way, one can reduce the waste problem on the one hand and at the same time obtain a climate-neutral fuel.

Battery recycling: Important for the environment and economy

"Modern batteries, such as nickel-metal hydride (Ni-MH) and lithium-ion batteries, consist of different components, which makes recycling and recovery processes technologically challenging," says Prof. Günther Rupprechter from the Institute of Materials Chemistry at TU Wien, head of the research project. "Improper disposal can lead to chemical leaks, fires, and pollution."

The recovery of nickel from spent Ni-MH batteries is also highly important economically: In the EU, waste batteries and scrap from battery production could provide around 16% of the nickel needed by 2030, which is enough to equip 1.3 to 2.4 million electric vehicles (EVs) annually.

Despite this potential, current recycling capacity in the EU and the UK is only about one-tenth of what is needed by 2030. Investments in recycling infrastructure are therefore necessary.

Upcycling: From waste recycling to CO2 capture

"Recycling is an important step, but even greater impact can be achieved by upcycling nickel into catalysts capable of producing fuels," says Dr. Qaisar Maqbool, first author of the study.

The team extracted nickel from used Ni-MH batteries and recovered alumina from used aluminium foil. These materials were then converted into a high-performance nanocatalyst in an environmentally friendly way – using green chemistry methods.

"Our nanocatalyst consists of 92-96% aluminium oxide and 4-8% nickel, which is optimal for converting the greenhouse gas CO2 together with hydrogen into methane," explains Günther Rupprechter. The process requires neither high pressure nor high temperatures, the catalyst works at atmospheric pressure and an easily achievable temperature of 250°C.

From greenhouse gas to clean energy

This provides a method for converting CO2 into a valuable fuel in a climate-neutral way: Methane plays an important role as an energy source in industry, for example. "Now we want to investigate how this process can be scaled up for technological applications," says Prof. Günther Rupprechter. "We believe that this approach can transform sustainable fuel production. Our approach shows a solution to the climate problem – and in a way that also helps to solve a pressing waste problem."

Upcycled material can also be recycled

Many catalysts deactivate over time – because the catalyst changes structurally at some point or becomes less effective due to the accumulation of coke (carbon). Such a deactivation was not detected in the study. Nevertheless, it was important to the team to think in closed cycles and to consider how the catalyst itself can also be recycled.

"To close the sustainability loop, you can recycle the spent catalysts back into their original precursors to be reused," says Dr. Qaisar Maqbool. This ensures that the entire process remains environmentally friendly, and the amount of waste is minimized.

Transforming battery/aluminium waste into nanocatalysts for methane (fuel) production and recycling spent nanocatalysts into catalyst precursors.

Credit

TU Wien