Sustainable biomass is working – a response to Ember

TL;DR: Sustainable biomass is supporting demonstrable year-on-year growth in forests. It also just helped the UK to go two months without coal for the first time since the industrial revolution. The campaign group Ember completely misread the science on forestry, called for carbon emissions to be double counted, then recommended a measure that would increase electricity bills.

The Ember campaign group (formerly Sandbag) has produced a paper that calls for an end to government support of biomass power.

It’s based on a misreading of the science, which leads its authors to make recommendations which would actually undermine the UK’s Net Zero strategy, which is embedded in a 2019 amendment to the Climate Change Act.

Not only that, but Ember notes the anti-biomass message this would send to other countries which are at earlier stages in their energy transitions away from fossil fuels such as coal. It would therefore undermine international efforts to fight the climate crisis.

We’ve taken some of the report’s key points and addressed the myths behind them.

The carbon debt fallacy


Sitting at the centre of this is the question of ‘carbon debt’. Without it, Ember’s argument is empty.

Put simply, critics of biomass agree that trees can recapture any carbon emitted by biomass power stations, but it takes decades for them to regrow, creating a ‘carbon debt’, which takes decades to pay back.

This is a misreading of how forestry systems work. It’s a question of scale. If we take one tree, cut it down and replant it, it will indeed take decades to regrow (about 35 years for faster softwoods, 80-120 years for hardwoods).

However, in a forest there are hundreds of millions of trees, and they’re at different stages of growth. This means that some will be mature, some have just been planted, some will be mid-way through their growth.

Therefore when the small portion that are harvested in a given year, about 2-3% of the forest in the Southern US region, there’s still 97% of the forest continuing to grow.

The graph below shows total forest inventory (scale on the left) compared to removals (scale on the right) in areas that supply Enviva, a major supplier of biomass to the UK.

The dotted black line is the removals for biomass – less than 0.1% of total inventory in a given year.

While all this is happening, total forest inventory is going up and up – carbon debt is not appearing.

Therefore the forest overall will almost immediately re-capture carbon emitted by the harvesting process. The other trees only need to grow by about 3-4% to balance out or even exceed harvesting, and this growth rate is ensured by active forest management, paid for by revenues from timber, joinery, pulp and paper and bioenergy markets. It wouldn’t happen at the same rate without active interventions.

It’s a matter of balancing growth and harvesting rates so that growth exceeds harvesting. That leads to year-on-year increases in the volume of growing trees, capturing more and more carbon each year.

This isn’t just a theory or a scientific model. It’s evident in the real-world data recorded over decades. The graph below is based on US Forest Service data and shows 70 years of increasing inventory (the amount of wood growing in the forest) in the Southern USA, all while supplying timber markets and, more recently, bioenergy markets too.

The point is, we don’t have to wait decades to recapture carbon – the forest as a whole is already doing it.


If the forest was in a state of ‘carbon debt’, then you’d see the lines going down (harvesting creating carbon debt), followed by slow recovery (repaying the debt). But in fact the lines are trending upwards.

Of course, there’s a big question here: wouldn’t it grow faster if we left it alone? The evidence suggests ‘no’.

When forests reach maturity, their overall growth tends to plateau. That’s because some trees are dying, others are growing, but overall mortality and growth level out. So the graph above would just show flat lines.

In fact, it’s possible for unmanaged forests to become net emitters, and this is increasingly a danger due to climate change.

Unmanaged forests are increasingly vulnerable to tree diseases (like Ash Die Back, which has been devastating to ash trees in the UK), infestations (like the boring beetles that have damaged vast numbers of trees in Canada) and forest fires (like the ones seen in Australia and California).

Markets for wood products help us to pay for investments in protective measures, such as managing the amount of dead material on forest floors, remove diseased trees and creating fire breaks or clearing deadwood that poses a fire risk.

On forest fires, it’s no surprise that California is actively looking at using bioenergy markets as one way to limit the risks, especially as the taxpayer-funded Forest Service experiences funding cuts.

In these markets, construction timber delivers the highest value, which also creates an incentive to grow big, tall trees and it leads to carbon being locked up in housing for decades – a win-win.

Other, lower quality materials, go to sectors including bioenergy, which tends to take the very lowest quality such as branches and misshapen or knotted wood.

The presence of these markets creates some very positive trends.

The graphs below show that, where wood product markets are active, we see higher growth rates, increases in forest land and increases in the amount of wood growing in a given area – all three mean more carbon is captured. And it’s true for softwoods and hardwoods.



Subsidies and value, or why biomass is worth public support

Knowing that we’re all concerned about money, Ember has focused its PR for the report on how much the UK has paid to biomass power stations, particularly Drax in North Yorkshire.

Yet they don’t show context, especially that these subsidies are to pay for 17% of UK renewable power – you’ll see subsidies paid to wind and solar, too, but that’s left out of Ember’s story.

Ember claims that you get more bang for your buck from wind, but this assumes that all electricity is the same. In reality, it’s not.

During the COVID-19 pandemic, we’ve seen a glimpse of the future, in which low-carbon energy sources are dominant.

This has created challenges for the grid, including ensuring that the system is stabilised and flexible enough to cope with ups and downs on an energy system which is rapidly evolving.

This requires particular technical services that biomass can provide, such as inertia, which basically smooths out the changes on the grid as energy sources ramp up and down and turn on or off, while demand is also fluctuating.

The costs of these services have been going up recently, partly because our system has low inertia, but biomass can offer it as a by-product of producing it low-carbon power.

Similarly, biomass offers useful things like long-term storage of energy (wood is basically a battery storing solar energy).

When the sun doesn’t shine or wind doesn’t blow, we need ready source of power. We don’t have battery technology that can provide this, so biomass is helping us to transition from fossil fuels to renewables.

These things are worth paying for, especially if we want a zero-emissions electricity grid by 2025, which is what National Grid is aiming for.

It’s also important to understand that biomass is laying the groundwork for negative emissions via healthy forest landscapes and Bioenergy with Carbon Capture and Storage (BECCS).

With BECCS, carbon is absorbed by trees growing, the trees are harvested and partly used to supply biomass power stations. Then the power station emissions are captured rather than released into the atmosphere. The carbon dioxide is then buried under ground or used in certain products.

Carbon Capture and Storage has been described by the UK’s Committee on Climate Change as “a necessity” for meeting Net Zero by 2050 and the CCC prescribed BECCS as a key component of large-scale zero-carbon industrial hubs.

BECCS is also a major player in two of the IPCC’s four pathways for avoiding catastrophic climate change.

Yet we won’t be able to deploy BECCS fast enough if biomass is undermined in the meantime. We need research and investment in technologies, supply chains and know-how if we’re going to implement BECCS, and that means supporting biomass now.

Drax in North Yorkshire is already conducting a pilot programme that capture one tonne of CO2 per day. We need to support this work, not hinder it, if we want to beat climate change.


‘Loopholes’, carbon neutrality and double accounting

Ember wrongly claims that there is a “loophole” in carbon accounting systems, allowing carbon emissions to be ignored.

The claim is based on the fact that biomass ‘stack emissions’ (a stack is the chimney of a power station, so ‘stack emissions’ refers to the power station’s emissions, as opposed to the supply chain’s) are counted as zero, because the biomass feedstock is regrown.

Ember sees this as accounting trickery, they think it ignores the forest’s carbon ‘account’. I.e. the forest could be losing (emitting) lots of carbon because of biomass power and it wouldn’t be noticed in the biomass supply chain.

In fact, international carbon accounting standards, which include biomass power, do count the emissions of biomass power, they just do it under the AFOLU (i.e. forestry) sector rather than the energy sector.

Amazingly, Ember leaves this out of their report – there’s no mention of the fact that biomass emissions are counted, but are counted at source, not at the stack.

They don’t seem to be aware of the UN’s carbon accounting of biomass at all, so it’s surprising to see them making recommendations about carbon accounting based on incomplete knowledge of the subject.

This accounting method exists because a) it’s simpler to track and b) it allows for transporting biomass across borders, which happens a lot given the uneven spread of forest resources around the world (for example, the Southern USA’s forests cover an area three times the entire landmass of the UK).

So, when wood pellets arrive at a UK power station, their emissions have already been recorded by the forestry sector wherever those trees grew.

Ember says that this ‘carbon neutrality’ approach is “outdated”. However, it was re-examined and reaffirmed just last year by the UN’s Intergovernmental Panel on Climate Change (IPCC) and has been endorsed by the UK’s Committee on Climate Change (CCC).

It’s worth noting that we do actually record the UK’s biomass emissions so that we have a more accurate idea of the energy sector, but not officially against international standards.

There’s more information on the carbon accounting question here.

If, as Ember suggests, we started to count the emissions at the power station as well, that would mean double-counting the same carbon emissions.

Firstly, that’s inaccurate and inaccuracy won’t help us in the fight against climate change.

Secondly, Ember says that these emissions must then be taxed, since the EU effectively taxes carbon emissions through its Emissions Trading System (ETS), which would raise electricity bills.

Such taxes inevitably end up on your electricity bill.

Effectively, Ember would like us all to pay higher bills in order to cover fictitious carbon emissions that they’ve dreamed up.

© 2019 Renewable Energy Association.