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Carbon Brief Staff

Carbon Brief Staff

26.11.2013 | 12:00pm
ScienceThe climate change benefits of high speed rail rest on decarbonising the power sector
SCIENCE | November 26. 2013. 12:00
The climate change benefits of high speed rail rest on decarbonising the power sector

The environmental argument the government has made for the HS2 high speed rail link could be weakend if the power sector is not decarbonised by 2030, according to official documents released yesterday. 

The coalition government is engaged in a political battle to persuade reluctant MPs to support the proposed high-speed rail network. Yesterday, it published a 400 page parliamentary bill, accompanied by a 50,000 page environmental statement. The documents effectively form a planning application for the first stage of the scheme, which will create a new rail link between London and Birmingham.

In the assessment, the government argues that HS2 will play a “key part in the UK’s future low carbon transport system” and will “support” the government’s overall carbon objectives. The government claims that the scheme will save about three million tonnes of carbon dioxide emissions over its sixty-year lifetime, as people choose to take the train rather than fly or drive.

But coalition battles over energy policy mean the Department for Transport’s calculations may be built on shaky foundations. High profile Tories – including chancellor George Osborne – continue to oppose a decarbonisation target.

The government’s climate case for HS2

Taking the train is less carbon-polluting than flying or driving. If HS2 was available today, the carbon emissions from taking the train from London to Birmingham would be about a quarter of those created by making the journey by car or flying, according to a consultancy report released at the end of last year.

A “modal shift” to rail will reduce emissions, the government says. It will make the transport system as whole less climate-polluting by increasing the total carrying capacity of the rail network for passengers and freight.

Of course, significant carbon emissions are associated with the process of building HS2 in the first place – for example in creating and transporting building materials, and disrupting agricultural land – as well as operating the project once it’s up and running.

But the government calculates that overall the project will help the government meet its carbon objectives, by about three million tonnes of carbon dioxide a year. Its modelling is based on two scenarios, as the following table shows:



Carbon savings associated with the first part of HS2, under two different scenarios modeled. Source: Department for Transport documents, published 25 November 2013

In both scenarios there is a reduction in carbon emissions as a result of the London to Birmingham train line. About a sixth of the saving comes from the government’s plans to plant more than four million trees along the route, in order to help it blend into the countryside, however. 

Assuming low carbon electricity 

There’s another important qualification here. The government’s calculations appear to be based on the assumption that emissions from the power sector are going to reduce dramatically over the next two decades. High speed rail is powered by electricity. The more fossil fuels are relied on to generate that electricity, the higher carbon it will be.

The government’s climate adviser the Committee on Climate Change (CCC) argues that if the government is to meet its climate objectives, the power sector needs to be virtually decarbonised by 2030. The committee says this means reducing the ‘carbon intensity’ of the sector to 50 grams per kilowatt hour (Kwh) of electricity by 2030.

The coalition disagrees. Chancellor George Osborne has suggested that the country should generate more power from gas, which would result in higher emissions. In June, the government rejected an amendment to the energy bill which would have created a binding target for 2030 decarbonisation, arguing that it isn’t needed.  

The modeling behind the HS2 environmental impact assessment

However, the modeling behind the Department for Transport’s documents, which is contained in a technical annex to the environmental assessment, assumes that the target is met. 

The graph below shows the modeling behind the DfT’s two scenarios on power sector emissions. The thick blue line shows the assumptions behind scenario B. In this scenario, carbon dioxide emissions from the power sector fall to 50 grams per kilowatt hour (Kwh) of electricity by 2030, consistent with the CCC’s recommendation.

In scenario A, power sector emissions reduce to about 100g/Kwh by 2030. This is consistent with the Department for Energy and Climate Change’s ‘ central‘ projection, and with the Liberal Democrat’s less ambitious suggested decarbonisation target.


Both scenarios represent a significant degree of power sector decarbonisation, and underpin the projections of environmental benefits the government makes for the project.

Earlier this year, Tim Yeo MP, chair of the Parliamentary Energy and Climate Committee wrote to the DfT expressing concern that a failure to decarbonise the electricity system will undermine the environmental case for HS2 – and asking if the DfT has any “contingency plans” in place in case it doesn’t happen.

It’s worth noting that a failure to decarbonise wouldn’t necessarily mean the HS2 project would increase the country’s carbon emissions. A report commissioned by various NGOs found that a scenario in which the UK built more gas plants reduced carbon savings from the London to Birmingham line by two thirds, but didn’t negate them entirely.

Image - CC via Flickr / Jon Curnow


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