How achievable is Net Zero Carbon?

Green Christian member Andrew Craig writes about the need for realism and commitment.

Since Prime Minister Boris Johnson first said, in February 2020, that the UK will be “net zero carbon” by 2050, “net zero carbon” (NZC) has become something of a buzz word. Other countries have made similar pledges. Corporations too have joined the bandwagon, including BP and Shell. Some of these pledges have been for NZC before 2050 – the Church of England was going to be NZC by 2045, but its General Synod then voted for 2030, the same as the Centre for Alternative Technology (CAT). Some environmental pressure groups want it to be even earlier than that – 2025. It’s an indication that some people consider that mitigation of climate change is now supremely urgent as well as important and are impatient for leaders to sort the problem out before it becomes too late.

But what does NZC actually mean? It means that human activity extracts as much greenhouse gas (GHG) from the atmosphere as it puts into it. This has to be achieved by reducing hugely the burning of fossil fuels and implementing measures that will sequester the same amount of carbon as is burnt, taking it out of commission. By GHG, we mean mainly carbon dioxide (CO2) and also methane (which is 30x more potent than CO2, but much shorter-lived in the atmosphere). Mainly we think of direct emissions, but we should not lose sight of our indirect emissions (the “carbon cost” of the steel, concrete, metals, plastics, food and other “stuff” that we consume and use).

Emissions can be divided into three groups – power generation, transport and everything else, which includes buildings, industry, commerce and agriculture.

(with kind permission of Dr William Bodel. Data: Committee on Climate Change and DUKES Digest of UK Energy Statistics)

Energy and Power Generation

In power generation, the UK has made good progress towards reducing emissions. Use of coal (the least carbon-efficient and most damaging fuel) is being phased out and, at times, sufficient renewable energy + nuclear power is already generated for us not to burn fossil fuels at all when demand is low. However energy demand is highly cyclical – daily, weekly and annually. To meet peak demand, gas-fired power stations, which can be rapidly turned on and off, will continue to have to be used for the foreseeable future.

Imagine a weekday morning during a winter cold snap – little or no wind and no sunshine at 7.30 am; even if your electricity supplier promises 100% renewable energy, the electricity coming through the plugs in your home is very unlikely to be generated from a renewable source. Most of it will be generated by Combined Cycle Gas Turbine (CCGT) generators that are brought into production at times of peak demand.

The key to decarbonising power generation further is storage: storing surplus power at times of low demand so it can be fed into the grid at times of high demand. The scope for pumped storage, a 20th century solution, is extremely limited. Battery storage and hydrogen are both needed: when burnt, hydrogen generates only water, not CO2. Battery storage can make a contribution – imagine the effect of tens of thousands of electric vehicles being charged overnight using off-peak energy. This would, of course have to be carefully incentivised and managed.

However, of the technical solutions, hydrogen is the most likely to give the capacity needed to manage a power grid based on renewable energy. Most hydrogen is generated through gasification of coal (or another form of carbon), which evolves huge quantities of CO2. If NZC is sought in a few years (rather than many decades), then Carbon Capture & Storage (CCS) (collecting and liquefying CO2, pumping it into secure underground stores, such as exhausted oil and gas wells) will be needed in the short term. Gasification is a well-established technology that was used to provide “coal gas” or “town gas” before North Sea Gas came on-stream in the late 1960s. Usually it is used to generate “Syngas”, an industrial fuel that contains mainly hydrogen, carbon monoxide and methane. CCS technology has been proved to work where there is a substantial point source (or nearby point sources) of CO2 – power stations or gasifiers[1].

Electrolytic hydrogen, made from water, is genuinely near-zero carbon. This is already generated and used, in the UK, but only on Orkney where there is a huge surplus of renewable wind energy; where large quantities are needed, it is a lot more expensive. A huge surplus of renewable energy needs to be generated before electrolytic hydrogen becomes viable over most of the UK. Energy bills will increase, but at least this offers some hope of reducing carbon emissions in power generation.


To reduce transport emissions, most hopes are pinned on electric cars – which, in turn depend on decarbonised power. The UK and California have both proposed banning sales of new petrol or diesel cars by 2035. Prices will come down, but at the moment they are expensive to buy and limited in range – and developing a unified charging infrastructure is not well advanced. Mining for lithium and other essential components has to be hugely expanded too, with environmental implications of its own. The technical challenges of designing viable and safe battery traction for commercial and agricultural vehicles, trains and shipping are such that hydrogen is more likely to be the preferred option, mainly through fuel cells.

I believe both battery traction and hydrogen fuel cell technology are needed to decarbonise transport. Lithium-ion batteries are the better option for smaller vehicles, but the high energy density (generating heat that has to be safely dissipated) and capacity limitations of batteries mean that they are unlikely to be the best solution for commercial vehicles and trains. Hydrogen fuel cells use hydrogen (from a pressure vessel on the vehicle) and oxygen to generate electricity (the opposite process from electrolytic hydrogen generation from water). The electricity generated provides the motive power to drive the vehicle. The problem with hydrogen (as opposed to petrol or diesel or LNG) is that it is difficult to liquefy, meaning that it has to be stored on the vehicle in a highly pressurised vessel for a fuel tank. On a small car this is cumbersome, although this is less of a problem on a larger vehicle, ship or train.

Could another option involve electrifying motorways in the same way as railways today? We used to have trolley buses.

Air transport faces the greatest challenges. Batteries and photovoltaics will continue to be inadequate to power any but the smallest aircraft. Airbus is looking to develop a commercial hydrogen-powered (turbo-prop) craft with a range of 2000 miles, but not before 2035. Jets, and aviation fuel, will continue to dominate for the foreseeable future. The only way to achieve deep cuts in emissions in the foreseeable future will be to fly a lot less.

Heavy industry, steel and construction

Which brings us to “the rest”, which includes heavy industry (including iron & steelmaking, metals, petrochemicals, plastics and fertilisers) and construction (which means cement, concrete, aggregates, bricks and steel). The biggest emitter is steelmaking – a blast furnace will emit several million tonnes of CO2 every year – but all of these are sizeable emitters of GHGs. Trading schemes such as the European Union Emissions Trading Scheme (EUETS) have been used to moderate emissions – permits to emit CO2 are allocated or sold to at the start of a period to participants, that can then trade permits, ensuring that they have sufficient to cover their actual emissions. There is considerable debate about whether or not trading schemes can bring about the reductions in emissions that are needed, or whether carbon taxation is also needed[2]. In any event, making carbon a lot more expensive than elsewhere in the world would, long term, result in these industries – and their emissions – being located in other parts of the world, where the “cost of carbon”, and environmental standards, are lower. If our NZC strategy involved getting rid of polluting industries, then, as well as losing the investment and jobs to the UK’s economy (often in places with above average economic deprivation already), we would be guilty of a similar sin to the Pharisees in Jesus’ time – making ourselves look morally clean by exporting our environmental “bads” elsewhere, with no overall gain in global emissions. The “circular economy” (recycling) is certainly one way of reducing harmful emissions – but even though recycling steel reduces overall emissions by about 75%, the remaining 25% are still a huge burden. The most effective way of containing global emissions from heavy industry is by reducing society’s consumption of its fruits!

Energy efficiency and heating 

The main fuel of heavy industry and commerce is natural gas (methane), which is also used to heat about 80% of our homes and most of our churches, schools and public buildings. Gas is between 3 and 4 times less expensive per kwHr than electricity. The UK uses nearly 50m tonnes of natural gas every year, generating about 135m tonnes of CO2. Consumption is falling slightly with improving energy efficiency of homes and processes. How are these emissions to be slashed? Building new homes to Passivhaus standards is a noble venture but simply not accessible to most people. All new buildings are much better insulated than before and many are designed to draw energy from alternative sources (electricity, heat pumps – even district heating). Some progress has also been made in installing better insulation and more efficient boilers in the existing building stock. However barriers remain, for example a widely held belief within the building trade that a low purchase price, not a minimal 30 or 50 year net cost, is what is important to their customers. High initial cost of housing is still a barrier to most people. Another barrier is the lack of incentive for some landlords to improve energy efficiency when they aren’t paying the utility bills. In any event, gas will continue to be the main fuel for most homes until most older housing has been replaced (30-40 years). New building also has an environmental cost – no one has yet shown me “zero carbon” bricks or cement.


One approach to this problem is biogas – methane from anaerobic digestion of organic material – which is considered to be “renewable” because the carbon is part of the normal “carbon cycle”, not liberated to the atmosphere from the deep fossil fuel store. In the UK nearly all biogas is made from waste materials (agricultural waste, food waste, landfill gas, sewage sludge). Other European countries grow crops specifically to generate biogas, but there is concern about the competition for land against the needs of agriculture and forestry. Most estimates from the industry are that biogas could replace about 10% of natural gas by 2030 (5) although others put the potential higher than that[3].

Woodlands as carbon sinks – a “natural climate solution” Credit: Annie Spratt on Unsplash

Tree-planting, habitat conservation and carbon sequestration

This brings me to the other side of the equation. How much can we do to sequester CO2 from the atmosphere, compensating for the emissions that will undoubtedly continue after the next 10 or 30 years? CCS is a short-term remedy, expensive but potentially applicable to large point sources of CO2 (industry, power), but this can only be a stop-gap measure and it will not be sufficient in the longer term. Corporations promise to pay for “offsets”, investing in forests, conserving habitats and restoring peat bogs; political leaders talk about planting billions of trees. These are inherently helpful and they make good press, but they are of doubtful value against the bulk of the fossil fuel emissions that will continue in the foreseeable future. In some circumstances, I believe that “offsets” are little more than carbon indulgences – giving absolution from guilt and salving the conscience whilst allowing Business as Usual to continue.

In particular, the use of wood as “renewable” fuel deserves closer scrutiny. Earlier this year the RSPB produced an excellent report entitled: “Woodlands for climate and nature: A review of woodland planting and management approaches in the UK for climate change mitigation and biodiversity conservation”, that communicates something of the complex relationship between woodland planting and environmental outcomes.

Is wood a “renewable” fuel?

Burning wood (or any other “renewable” fuel) releases CO2 to the atmosphere just the same as fossil fuel. The difference is that wood can be part of a carbon cycle of a few years to a few decades, whereas the carbon cycle for fossil fuels is tens or hundreds of millions of years. To sequester carbon, it must be taken from the atmosphere and incorporated permanently in soil (the biggest carbon sink on earth) and trees, not just re-released a few years later. A good question to ask is: if this wood were not burnt, what would happen to the carbon? The most effective practice, planting mixed deciduous woodland and leaving it alone, is reckoned to abstract up to 7 tonnes of CO2/hectare per year (a bit less than the carbon footprint of an average household). However these rates of sequestration are not achieved for at least 10 years after planting[4]. Most forestry is “managed”, usually commercially, and coniferous (sometimes with deciduous trees on the margins to improve appearances). Monoculture forestry degrades soils, impoverishes biodiversity and only sometimes achieves a net carbon “gain”, depending on circumstances. In particular, planting trees in peat actually releases more carbon from the soil than it stores in the wood. Also important is what is done with the wood. For example, harvesting North American or European forests to feed the Drax power station is deleterious, especially taking into account the “carbon cost” of cutting, handling, chipping, drying and transporting the wood[5]. Planting Sitka spruce for papermaking is not much better as papermaking is extremely energy intensive (though bark is sometimes used as “renewable” fuel to generate steam for the process).

Using wood for buildings and furniture at least takes some of the carbon out indefinitely – although the carbon sink thus created is small. Despite its high CO2 emissions relative to methane gas, Energy from Waste (EfW) is sometimes justified (erroneously) by calling it “renewable”. As this waste would otherwise be landfilled if not recycled, this is false – landfill is extremely wasteful of natural resources, but at least it takes most of the incinerable material, the carbon in plastic and wood, out of the atmosphere.

Taking the long view 

So the UK’s capacity to sequester additional carbon from the atmosphere is very limited in the short term. Reversals are needed: of many decades of agricultural practice that has reduced the amount of humus in soil, relying on chemical fertilizers to achieve high crop yields; of construction of roads and hard standings where land had previously absorbed CO2; and of the continued destruction of ancient woodland (notoriously, over recent months, to make way for HS2). These have to be reversed, before new carbon sinks are established that can, over time, contribute to NZC. New forests and restored peatlands are essential, but they are just the start of centuries of work, reinstating natural systems that will compensate for anthropogenic emissions. NZC is certainly unrealistic within 10 years and will only be realistic within 30 years if there is a sustained political effort supported by voters. However there is a danger that exaggerated claims about carbon sequestered in forests, and even double counting “renewable fuel” as sequestration, could take the focus away from the most urgent need to reduce emissions.

We should hold the Government to account for its pledge that the UK will achieve NZC by 2050, demanding detailed plans and milestone targets for reducing emissions. Most of the reductions, the “low hanging fruit”, should be made within the next 10 years.

The need for change

I have dealt with many technical issues in this article, but actually what is most important is helping bring about a cultural change whereby the majority of citizens and voters will accept, and ask for, less consumption, less choice, less meat, increased taxation, more expensive cars and less foreign travel – because this is what better stewardship of our planet for the benefit of future generations requires: a lower financial “standard of living” for many, but a higher standard of life for the planet that supports us and the 10s of millions living elsewhere who are already suffering the consequences of climate change. I don’t think the generation I belong to will do it – most are too set in their comfortable ways. Can the younger generations make the leap in imagination and persuade politicians and corporations that that is what they will vote for?

Green Christian member, Revd Andrew Craig once numbered among Resource Magazine’s “Hot 100 movers and shakers in the waste management world”. He was a researcher in industry in plastics and additives, before working as a chartered environmentalist for local authorities. He coordinated a climate change strategy for the Tees Valley before more recently working in parish ministry in and around Hartlepool.

A shorter version of this article will feature in the Spring 2021 issue of Green Christian Magazine.

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  1. (2020)
  4. Forests for a low-carbon future (2016)



Author: Paul Strickland | Date: 22 February, 2021 | Category: Uncategorized | Comments: 3

Comments on "How achievable is Net Zero Carbon?"

Iain Climie:

March 5, 2021

Excellent point as the economic system boils down to "make more money and buy more stuff". Also one recent estimate is that 11 fully used planets would be needed for everyone to have well-off US lifestyles and jobs to afford them while I suspect that doesn't consider rehoming climate refugees. To worsen matters further, as ice sheets melt they reflect less solar energy, exposed darker surfaces absorb more heat, previously frozen deposits release gasses while dying vegetation and fires worsen matters further. There are severe risks in trying geo-engineering like Solar Radiation Management but it may yet become necessary unless something unexpected happens e.g. a VEI 7 eruption like Tambora in 1815 which dramatically cut solar input. That brings its own problems of course but we really are in deep trouble. Ironically many measures like reducing waste which would have been effective regardless of the nature, direction, extent and cause of climate change would have made perfect sense regardless but humanity wasted decades bickering about who is right on the topic.


March 5, 2021

The challenge is arguably more fundamental than you describe. Consumption(which is in reality is mostly a form of consumerism) drives the current economic profiles of most western societies. A large number of jobs are tied to consumerism therefore to reduce the number of items purchased unsustainably, jobs and livelihoods will need to be developed for the large number of people who's jobs need to be displaced to reduce consumption. An arguably more difficult challenge than reducing carbon emissions itself.

Iain Climie:

February 22, 2021

It may not be enough as once frozen gas deposits are escaping, less ice reflects less solar energy, the darker surfaces exposed absorb more heat while fires and dying vegetation worsen matters further. The question of rehoming climate refugees (and ensuring they have jobs, food, clothing, healthcare etc) is also on the agenda of very few politicians. Carbon capture and even solar radiation management may be needed

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