HomeElectrificationAchieving net-zero

Achieving net-zero

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The 2008 Climate Change Act was the first in the world to make a government legally accountable for delivering its greenhouse gas (GHG) emissions target, which was at least 80 per cent lower than the 1990 baseline. The Act is the basis for the UK’s approach to tackling and responding to climate change. It requires five-yearly carbon budgets to be set and established the Committee on Climate Change (CCC) to provide independent, expert, evidence-based advice.

By 2017, the UK was over half-way to meeting its 2050 target with GHG emissions 43 per cent below those of 1990. However, this was not good enough as this was largely achieved through the relatively easy measures of burning gas instead of coal and using more renewables to generate electricity. Furthermore, it was becoming increasingly clear that the 80 per cent reduction target was not enough.

In May 2019, the CCC published its report ‘Net Zero: The UK’s contribution to stopping global warming’. This reviewed the latest scientific evidence on climate change and concluded that the UK should adopt a target of net-zero GHG emissions by 2050 which, if replicated across the world, would deliver a greater than 50 per cent chance of limiting the global average temperature increase to 1.5°C.

The report considered this target was achievable as the technologies and approaches to achieve net-zero are understood. However, it was also considered to be hugely demanding and only achievable if there is urgent government action to drive the significant urgent policy changes required.

In June, the CCC’s net zero 2050 target became legally binding as the Climate Change Act was amended to adopt it.

Achieving net zero will affect everyone in Britain and require some lifestyle changes. Yet, whilst some might believe that reducing emissions requires an economic slow-down, the good news is that it need not make the UK poorer. The CCC report explains the technologies needed to both reduce emissions and maintain economic growth as well as the policies that the government must adopt if these technologies are to be deployed.

The technical report that supports the CCC’s recommendation is available online and is a daunting 304 pages. For this reason, we thought our readers might appreciate a summary, especially as this report provides the context for rail decarbonisation.

Electrify everything

As fossil fuels have a high energy density and can be readily stored and transported in fuel tanks, tankers and pipelines, it is not surprising that the modern world is utterly dependant on them. However, if net zero is to be achieved, we must be weaned off them. To do this, the CCC report stresses the need for extensive electrification, particularly in respect of transport and heating.

The obvious reason for this is that electricity can also readily transport huge amounts of energy, albeit only to fixed locations. An exception to this is electric trains, which are thus the only form of high-speed and mass transport that offers potentially zero emissions. No doubt for this reason, the report recommends a rolling programme of railway electrification, otherwise rail transport is hardly mentioned except for the need for modal shift from road and air to rail. Yet any significant modal shift would require a huge increase in rail capacity, such as that HS2 will provide.

The CCC report considers that the electrification of road transport (19 per cent of the UK’s GHG emission) will be by battery and hydrogen-powered vehicles. Advances in battery technology and the provision of the required charging infrastructure will make electric cars increasingly practicable, so that no more petrol or diesel vehicles should be sold after 2030. However, the report points out that the solution for HGVs is not clear and is likely to be a combination of hydrogen and battery technology, such as extremely fast chargers at motorway service stations. It also moots the use of a motorway pantograph system to continuously charge HGVs.

Electrical industrial and domestic heating is also essential to reduce fossil fuel consumption. The report notes that there is an urgent need to engage with the public on a strategy to move away from gas heating as GHG emissions from buildings accounts for 17 per cent of UK emissions. It envisages that electricity should be used to power heat pumps to heat buildings as this would produce three units of heat for one unit of electricity. There is also the potential to use hydrogen in the existing gas distribution system to heat buildings.

By 2050, the UK will require a low-carbon electricity generating capacity of 150GW to generate a total of 645TWh to satisfy this extensive electrification. This compares with today’s 104GW which produces 300TWh. The CCC envisage a vast increase in solar, off-shore and on-shore wind generation. However, its scenarios take a cautious approach, limiting the share of variable renewables to under 60 per cent as these are not suitable for base load and peak power which needs to be supplied by nuclear power and gas turbine plants with carbon capture and storage (CCS).

Aviation and shipping

Aviation and shipping accounts for 10 per cent of UK GHG emissions and, unfortunately, cannot be electrified except perhaps for short distance domestic shipping. Aviation makes up seven per cent of the UK total, of which 96 per cent is international flights from which emissions have increased from 15 to 35MtCO2e (Metric tons of carbon dioxide equivalent) between 1990 and 2017.

By 2050, there are unlikely to be any commercially available zero-carbon planes. Measures to manage aviation emissions will therefore include more efficient engines and airframes, improved airspace management, the use of sustainable alternative fuels and measures to reduce growth in demand. While biofuels could be a substitute for aviation fuel, this might not be the best use of this scarce resource for which there are alternative uses that may save more emissions. Synthetic carbon-neutral fuels are another alternative, although it is likely their costs will be very high.

There are a range of options to reduce shipping emissions, some of which may allow shipping to get to near-zero emissions. These include more efficient hull and engine designs, improved operations and the use of alternative fuels such as ammonia and hydrogen.


One key technology that has yet to be developed is Carbon Capture and Storage. In contrast, the production of biofuels is a well-developed technology and accounts for three per cent of road fuels. However, there is a finite limit to its production, given land constraints and the requirement for food production, and growing biomass requires a significant carbon input. Therefore, the production of bio energy with CCS (BECCS) is required if biofuels are to contribute to the net-zero target.

CCS can capture and store up to 90 per cent of the GHG emissions associated with fossil fuel power generation and industrial processes. The UK’s first carbon storage facility is expected to be operational by the mid-2020s. This will capture 200,000 tonnes of CO2 from a gas terminal near Peterhead and use the existing pipelines to store it in a depleted gas field.

By 2050, the CCC expect the annual UK storage requirement is expected to be about a thousand times this amount (i.e. 176 million tonnes of CO2). Storage potential is not considered to be a constraint for the UK, which has sufficient geological capacity to store CO2 at this rate for 500 years. Exhausted oil and gas fields and their pipeline infrastructure present significant CCS opportunities.

The net-zero report also envisages that hydrogen should be produced by methane reforming with CCS for the resultant CO2 emissions. Hydrogen needs to be produced in this way as if it was all produced by electrolysis. This would increase annual electricity production by 400TWh (more than 50 per cent of the projected 2050 demand). It predicts that, by 2050, UK hydrogen use will be the annual equivalent of 270TWh (compared with 27TWh in 2017).

Most of this hydrogen is required for heating, both to satisfy industry’s requirement for high temperature gas heating and to be used in existing domestic gas distribution networks. Buses and trains would require respectively 3TWh and 0.3TWh, a small fraction of total hydrogen production. Unlike heating, the hydrogen used in fuel cells must be of a very high purity and so is better produced by electrolysis. This would be a more appropriate option where train depots may be some distance from a large steam reforming plant but could be close to a wind farm and use otherwise unwanted energy during the night, for example.

Land and lifestyle

In 2017, the UK’s woodlands absorbed two per cent of Britain’s GHG emissions or 10MtCO2e. The report envisages that annual afforestation rates of between 30,000 and 50,000 hectares would increase woodland cover from its current 13 per cent of the UK’s land area to between 17 and 19 per cent, so increasing this carbon sink to between 16 and 36MtCO2e by 2050.

In contrast, the biological processes inherent in crop and livestock production make it impossible to reduce agricultural non-CO2 emissions to zero. Currently, agriculture accounted for nine per cent of all UK emissions, half of which were from ruminant livestock. The report considers that there is significant potential to reduce emissions by more efficient use of nitrogen, better manure management, improved crop productivity, better thermal efficiency of agricultural buildings and low-carbon alternatives for tractors and other machinery.

The report shows how consumer lifestyle choices can help to reduce agricultural emissions as healthier diets rely less on carbon-intensive animal products (like lamb, beef and dairy). Reducing food waste is also a key step that individuals can take to reduce emissions as a significant amount of agricultural land is devoted to the production of the 10 million tonnes of food which are wasted each year, of which 70 per cent is binned within households.

Other lifestyle choices to support net zero emissions are indicated by the current breakdown of average household emissions which are: heating (31%), transport (27%), diet/agriculture (18%), aviation (12%), electricity (9%) and waste (3%). Whilst the reduction of GHG emissions from heating and electricity will largely come from technological improvements, other aspects require changes in consumer behaviour such as diet and waste. The CCC report mentions the requirement to make more use of public transport and to fly less, noting that the growth in air travel cannot be unfettered.

Who pays?

Net zero by 2050 is estimated to cost between one and two per cent of GDP, which is the same cost of the 80 per cent target which Parliament accepted when the 2008 Climate Change Act was passed. Incidentally, it is also similar to the entire defence budget (1.8 per cent in 2018).

As well as savings from the avoidance of climate damages, the CCC considers that there are likely to be significant benefits from the required decarbonisation programme. These include better air quality, energy self-sufficiency, with little demand for imported fossil fuels and their associated price volatility, and industrial opportunities from the UK being the first to adopt such a radical carbon reduction programme. For example, delivering the goals of the Paris Agreement will require annual $2 trillion global investment in low-carbon technologies up to 2050.

Delivering this ambitious net-zero programme will require significant capital investment for which the report recommends that HM Treasury undertakes ‘a thorough review of the costs and benefits of meeting a net-zero target and the appropriate policy levers to achieve an efficient and fair transition’ to attract sufficient low-cost capital. In this respect, it considers that ‘cost-benefit analysis (CBA) is not suitable for climate change action’.

The CCC is clear that decarbonisation action must progress with far greater urgency. Of all its recommendations, perhaps the most urgent is ensuring that the right financial levers are in place. The required investment may not be forthcoming if government investment appraisals do not adequately value carbon savings.

As an example, business cases for projects that deliver the required modal transfer from road to rail are weakened under current rules which require them to take account of the cost of the resultant loss of fuel duty. No doubt such decarbonisation disincentives will be addressed, otherwise there is little chance of achieving substantial carbon reductions.

The net-zero report shows the huge changes that will need to be made across all sectors. It is a bold vision which includes the following issues relating to the rail industry:

  • The benefits of electrification generally and for rail the requirement for a rolling programme;
  • That there will be far greater use of battery and hydrogen technology in the automotive sector than on rail;
  • That biofuels and synthetic fuels are likely to be a scarce resource, the use of which may only be justified in applications for which there are no other zero-carbon options;
  • The requirement for modal shift from road and air needs a significant increase in rail capacity, such as that provided by HS2;
  • The urgency to act now;
  • If net zero is to be achieved by 2050, the need for Government financial policies that incentivise carbon savings.

A credible rail decarbonisation programme must address these issues.

This article first appeared in Issue 177 of Rail Engineer, Aug/Sep 2019.

David Shirres BSc CEng MIMechE DEM
David Shirres BSc CEng MIMechE DEMhttp://therailengineer.com

Rolling stock, depots, Scottish and Russian railways

David Shirres joined British Rail in 1968 as a scholarship student and graduated in Mechanical Engineering from Sussex University. He has also been awarded a Diploma in Engineering Management by the Institution of Mechanical Engineers.

His roles in British Rail included Maintenance Assistant at Slade Green, Depot Engineer at Haymarket, Scottish DM&EE Training Engineer and ScotRail Safety Systems Manager.

In 1975, he took a three-year break as a volunteer to manage an irrigation project in Bangladesh.

He retired from Network Rail in 2009 after a 37-year railway career. At that time, he was working on the Airdrie to Bathgate project in a role that included the management of utilities and consents. Prior to that, his roles in the privatised railway included various quality, safety and environmental management posts.

David was appointed Editor of Rail Engineer in January 2017 and, since 2010, has written many articles for the magazine on a wide variety of topics including events in Scotland, rail innovation and Russian Railways. In 2013, the latter gave him an award for being its international journalist of the year.

He is also an active member of the IMechE’s Railway Division, having been Chair and Secretary of its Scottish Centre.


  1. I hope we are not barking up the wrong tree with this concern about carbon dioxide.

    Being a science graduate, I would expect to be able to understand how the Greenhouse Effect works, but have not seen a convincing explanation for how a concentration of one part in 2,500 of the gas can have such a disproportionate effect. The greenhouse effect theory has been around for over a century, when it was first noted by the Swedish chemist, Arrhenius. However, carbon dioxide absorbs infrared radiation (IR) in three narrow bands of wavelengths, which are 2.7, 4.3 and 15 micrometers (µM). This means that most – about 92% – of the heat producing radiation escapes it. About 8% of the available black body radiation is picked up by these characteristic frequencies of CO2.

    Can someone please explain how a concentration of 1 part of carbon dioxide in 2500 can cause a greenhouse effect?


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