More than a numbers game

15th January 2024


Matt Tompsett looks beyond tree planting to the pros and cons of land and sea-based carbon sequestration projects.

More and more organisations are turning to tree planting in order to meet their net zero or carbon neutral targets. It’s no secret that trees are very good at sequestering carbon from the atmosphere, but should it all be about planting as many trees as possible?

First of all, let’s address the issue of net zero Vs carbon neutral. These are very different things, and we still hear a lot of people and organisations confusing the two. Carbon neutral is about balancing your emissions. An organisation could reduce their CO2 emissions by any amount (say 20%), offset the rest (80%) by planting trees and claim they are carbon neutral. This is not an approach we should be encouraging. The Science Based Targets initiative has now defined net zero as a minimum CO2 reduction of 90%, so therefore allows only offsetting residual emissions, but to a maximum of 10%. It is this definition we should all be encouraging and following. It would be unrealistic to believe that all organisations will be able to reduce their CO2 emission by 100% over the next 2-3 decades. Therefore, in order to reach their net zero targets, the majority of organisations will look to offset a maximum of 10%. Currently, most organisations will look to offset these residual emissions by planting trees.

The UK is one of the most deforested countries on the planet and there needs to be a concerted effort to reforest large areas of the country. Tree planting is a valid, tried and tested, certified way of offsetting emissions. Many organisations have this built into their net zero plans and we are seeing many announcing tree planting targets i.e. we will plant 1 million trees by 2030. But is this the right approach?

The carbon absorption capacity of trees varies greatly from tree to tree, even those of the same species. There are many factors to be considered, including the species, age, size, location (what habitat is already on the site), weather conditions, the type of soil and of course, will it be maintained properly. Many think that once a whip is planted, job done. However, a whip is simply a baby tree, and all babies require some care and attention. Aftercare for new planting is crucial, but often overlooked. A tree, for the first five years of its life, is a source of carbon not a sink. So, if a tree doesn’t survive into maturity, it is a waste of time and money and a source of carbon. When a tree dies and decays, or if it is burnt, any CO2 sequestered over the course of its life will be returned to the atmosphere.

Some trees grow more quickly than others and therefore absorb CO2 faster, other species grow slower but also live longer and therefore absorb and store more CO2 over the long term, such as oak or beech. Ultimately a tree’s ability to sequester and store CO2 comes down to the size of its canopy. The successful delivery of ecosystem services such as carbon sequestration and storage are all about leaf surface area, so a bigger and healthier the canopy the better. These canopies will also deliver other vital ecosystem services such as shading, pollution removal, storm water attenuation and of course increase biodiversity.

The old adage applies here, it’s more about quality than quantity. A more meaningful target related to trees for organisations to adopt should be about increasing canopy cover, i.e. we will increase canopy cover across the borough by 50% by 2030. Instead of spending a million pounds on a million trees, spend a million pounds on half a million trees, but make sure they are of good quality stock, healthy at the point of planting, are the right species, in the right location and will be maintained properly to ensure survival.

More effort made to ensure the health of existing trees with appropriate planning and management is vital. This includes recognising the value of this natural asset and the services it provides, with suitable resource and budgets, and rethinking the traditional ‘maintenance liability’ view.

Tree planting is certainly an effective CO2 removal and storage technology, but it is not a numbers game. More time and effort needs to be spent on retaining and increasing tree canopy in local authorities and across the country, and this can only be achieved by planting the right tree in the right place and making sure it is maintained to reach maturity.

Currently, the majority of carbon offsets available on the voluntary carbon market are linked to tree planting and soil restoration projects. The voluntary carbon market enables companies to buy carbon credits (offsets) as part of their CO2 reduction commitments. In 2021, the value of carbon credits traded on the voluntary market exceeded US$1 billion, more than double the value in 2020. If tree planting was the only offsetting solution, globally we will need to plant enough trees to cover a billion hectares (the size of the USA and Canada), which is unrealistic and, in some locations, driving negative social impacts and land use change. Many of the locations targeted by offsetting schemes are in lands where Indigenous or local rights have not been secured. Most of the countries looking to benefit from carbon markets have not yet defined communities’ rights over the carbon held in their lands and territories.

This situation poses a risk both to local communities who face increased threats of land grabs, criminalisation, conflict and other human rights violations, and the viability of carbon markets themselves. We’ve seen this overseas where a Kenyan program for reducing deforestation has led to the eviction of Indigenous people from their traditional lands. Closer to home we’ve seen large corporations buying up huge areas of land in Scotland to offset emissions, pushing up land prices, rent and displacing local people.

The voluntary carbon market is set to grow rapidly as countries and companies seek to meet their emissions reduction targets and as it does so will the benefits and risks faced by Indigenous peoples and local communities. We need to look at other solutions.

But what about other natural carbon removal and storage technologies, are trees the only option when it comes to removing CO2 from the atmosphere via the creation of natural habitat?

Blue carbon is a relatively recent term that refers to marine and coastal habitats ability to remove and store CO2 from the atmosphere and the ocean. In the UK, the most common examples of blue carbon are salt marshes, kelp forests and sea grass meadows, however, internationally can include habitats such as mangrove forests. Just like trees, as these habitats grow, they remove CO2 from the air and ocean and store it in their leaves, branches, and roots. This CO2 is then trapped in the seabed or sediment when the leaves drop or the plant dies. The ocean is the biggest carbon sink we have. It has absorbed around 50% of all the CO2 we’ve emitted as a species. When these blue carbon ecosystems are damaged, an enormous amount of CO2 is emitted back into the atmosphere. Worryingly, almost a third of the world’s seagrass has been lost in the last century (a 92% loss in the UK alone), the world’s mangroves are being lost at a rate of 2% a year, and less than half of the world’s salt marshes now survive (an 85% loss in the UK).

Blue carbon has several advantages over terrestrial alternatives such as trees. Blue carbon habitats are much quicker growing which means they can sequestrate CO2 significantly faster. Studies suggest that sea grass is up to 40 times more efficient at sequestrating CO2 than trees. They reduce coastal erosion by absorbing wave energy produced by storms, improve water quality by filtering pollution from the water column, including microplastics. They support a huge variety of biodiversity, often more than terrestrial woodlands, supporting food chains that are the foundation of all life on earth. This in turn benefits commercial fisheries and recreational opportunities. But possibly one of the biggest advantages is the space the ocean provides and scope to scale up the creation and restoration of these habitats.

This scaling up of blue carbon can be delivered with fewer social impacts. For example, it may result in more protected ‘no take zones’, which studies suggest boost fishing yields for the fishing industry, and there are no Indigenous people at threat from eviction from the sea bed.

The concept of blue carbon is several years behind its terrestrial counterpart. However, it’s catching up fast. The pilot of a UK Saltmarsh Carbon Code has just been completed. This will create a rigorous and scientifically based voluntary certification standard and enable saltmarsh carbon to be confidently purchased, thus providing an income stream for restoration projects. One of the main objectives of this initiative being to promote wider discussion around applying this approach to develop a UK Blue Carbon Code inclusive of a range of coastal habitats, including sea grass.

It is clear that tree planting alone, even if done correctly, will not be enough. We need to look at other solutions, such as investing in blue carbon habitats.

Matt Tompsett MIEMA is a member of IEMA’s Energy and Climate Steering Group

Image credit: Shutterstock

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