What’s in a tree: how effective is carbon offsetting?

Tree planting on a massive scale could suck millions of tons of carbon from the atmosphere, but dubious offsetting schemes and poor land management threaten to derail the programme


  • Stephen Cousins

23 November 2021

Kaleidoscope effect of trees

Implicit to the global drive to reach net zero and prevent catastrophic global warming, is the need for businesses and organisations to target net zero within their own operations.

That means achieving a balance between reducing the amount of greenhouse gas emissions they produce and actively removing emissions from the atmosphere through carbon offsetting.

Almost all the pathways developed by the Intergovernmental Panel on Climate Change (IPCC) rely on methods to enhance land-based carbon sinks. Among them, carbon sequestration through tree planting is considered key to reducing emissions at a meaningful scale.

“The years ahead will need to involve vast areas of afforestation,” explains Werner Kurz, a research scientist at Canada's Pacific Forestry Centre who is leading the development of an accounting system to assess potential climate change. “According to some estimates we need more than 700m hectares of trees. That’s double the size of India.”

Businesses, including building developers and other construction firms can invest in tree planting by purchasing carbon credits, either voluntarily or in response to regulation. The OECD says that more than 100 countries have laws or policies in place that require or enable the use of biodiversity offsets, many of which involve tree planting.

In the UK, the soon-to-be enacted Environment Bill will require all sites being developed to achieve biodiversity net gain, which is expected to involve extensive planting both on- and off-site.

UK councils already have the power to require developers to pay for offsets to make up for carbon saving shortfalls on their projects, which are collected through ‘Section 106’ legal agreements attached to planning consents.

Carbon converters

The carbon converting power of trees is already proven, roughly 50% of the dry weight of wood is carbon removed from the atmosphere through photosynthesis. According to some estimates, an acre of new forest can absorb around 2.5 tons of CO2 per year, more than half the carbon footprint of the average person (around 4.8 tons per year).

Leaders worldwide are convinced of the benefits – the European Commission’s forest strategy includes a goal to plant 3bn trees by 2030. The UK Government plans to plant approximately 7,000 hectares of woodlands per year by mid-2024.

However, in the rush to cut emissions, many tree planting initiatives have proved ineffective or counterproductive, leading to accusations of ‘greenwashing’.

Afforestation projects sometimes fail when land is subsequently sold off for commercial development or other purposes. Dubai’s One Million Trees initiative was set up in 2010 to increase green areas in the city through new planting. At its peak, the tree nursery measured 130,000m2 and irrigated the plants using recycled wastewater and desalination. But after just a few years the land was sold, by investment holding company Dubai Holding, to build the world’s largest shopping centre.

Trees can, paradoxically, be wiped out by the very impacts of climate change, such as severe droughts, wildfires, flooding or tree diseases. For example, planting trees in a grassland or shrubland setting can increase the continuity between adjacent forests and contribute to the spread of fire.

It’s imperative to properly identify locations that are compatible with afforestation, says Kurz: “We still need to plant, while acknowledging that there will be a percentage of that area lost to fire. How much is lost depends on where we plant. Sweden, Norway and Finland have very dense road networks and are really capable of suppressing wildfires. In places like Canada and Russia, population density is so low there are vast areas without roads, in which case it can be better to plant on abandoned agricultural land with existing road infrastructure.”

A further cause for concern is a failure by decision makers to appreciate the true long-term cost of tree management and care. Thousands of saplings were planted by the controversial HS2 rail project in the UK, to compensate for ancient woodlands destroyed. But the saplings were deliberately neglected during a heatwave in 2018 because it was considered more cost effective to simply replace them rather than water them.

Environmental certification

Questions over farming and forestry practices paid for by carbon credits have led to calls, by climate and biodiversity experts, for tighter standards and certification schemes. This would help to ensure that businesses have confidence in the projects they invest in.

One industry-leading example is the Woodland Carbon Code, a voluntary standard for woodland creation projects in the UK, backed by the government and the forest industry, which checks claims made about carbon offsets and provides ongoing verification and certification. Other trusted third-party organisations include Gold Standard, Verified Carbon Standard, Climate Action Reserve, and American Carbon Registry.

Even more stringent is California, where offset credits must be verifiable, quantifiable, enforceable and produced based on a California Air Resources Board-approved protocol.

On the flip side, efforts to reach net zero will also require incentives to encourage farmers and foresters to reforest or improve how they manage the existing woodland stock.

“Mismanagement is usually the result of projects not being economically viable and that often comes down to land economics, where the incentives need to be stronger,” says Christopher Williams, chief executive of the Royal Forestry Society. “In the UK, woodlands are not only failing to maximise their carbon capture potential, they’re failing to maximise biodiversity value, they're often dark and dingy and not accessible to people. The prices of timber have gone up, which potentially could bring more woodland into management.”

Paul Collins FRICS, senior lecturer at the School of Architecture, Design & the Built Environment at Nottingham Trent University, and board member for the Green Roof Organisation, says: “Green roofs and walls are also part of a nature-based approach to the [net zero] challenge. Green roofs can have a moderating effect on the micro-climate and in number can mitigate against urban heat islands.

“Currently a very tiny number of buildings use timber in a structural way, but glulam (glue laminated timber) framed and off-site manufactured timber buildings are an opportunity for the future. It’s down to clients and their advisors to specify them.”

Then there is the overriding need for businesses to focus on stemming emissions at source rather than rely on offsets as a crutch for bad environmental practice. “We must not as societies use these nature-based solutions as an excuse to not reduce fossil fuel emissions,” says Kurz. “It's really critical that we reduce emissions as quickly and as aggressively as possible.”

There’s no silver bullet to achieving net zero and most climate experts agree that a patchwork of different solutions for carbon sequestration will be needed in the years ahead.

That means afforestation, woodland restoration and other nature-based solutions such as the enhancement of soils, peat bogs and pastures, and using more wood in buildings, such as mass timber, to lock in greater levels of carbon.

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