In R (on the application of Boswell) v Secretary of State for Transport [2024] EWCA Civ 145 the Court of Appeal considered the extent to which the cumulative carbon emissions of a nationally significant infrastructure project should be assessed.

Key Points

  • A wider assessment of cumulative carbon emissions for nationally significant infrastructure projects will not always be appropriate or required.
  • The method used to assess the cumulative carbon emissions of any project is a matter for the decision-maker, challengeable only on rationality grounds.
  • Carbon emissions have no geographic boundaries and so, on current scientific knowledge, there is no meaningful way to carry out a wider assessment of cumulative emissions.


The claimant sought judicial review of the Secretary of State’s (“SoS”) decision to grant Development Consent for three separate road improvement schemes to the A47 around Norwich, which were designated as nationally significant infrastructure projects (“NSIPs”). The High Court had dismissed the three related claims, noting that the case was effectively a challenge to the acceptability of the carbon impacts from the three schemes, which was not a matter for the courts.

The Court of Appeal was dealing with a single ground of appeal, namely whether the SoS had in the three separate decisions for the schemes lawfully discharged the obligation to examine and assess the cumulative greenhouse gas (“GHG”) emissions likely to result from each of the proposed developments – an obligation arising as part of the Environmental Impact Assessment process applicable to NSIPs.

Dr Boswell did not challenge the methodology used to quantify the likely increase in carbon emissions in each separate environmental statement, or the comparison of the projected emissions from each scheme with national carbon budgets. Dr Boswell instead contended that there was a lack of comparison between the combined emissions from each scheme and related projects with those national carbon budgets. As such, Dr Boswell argued that it was not possible to know whether the combined emissions would have a material impact on the Government’s ability to meet national carbon reduction targets.


The Court of Appeal noted the policy position that any increase in carbon emissions is not a reason to refuse development consent, unless the increase in carbon emissions resulting from the proposed scheme are so significant that it would have a material impact on the ability of Government to meet its carbon reduction targets under the Climate Change Act 2008, including the net zero by 2050 target. Carbon budgets are set to ensure progress towards this target.

It was also accepted that the SoS did direct his mind in each decision to the question of the cumulative GHG effects of the scheme at some length. He had before him, and must have given consideration to, the forecast emissions from each of the three schemes, together with the forecast emissions from other existing roads and planned projects (including the other two schemes). It was not therefore the case that each scheme was viewed in isolation. Rather, it was placed within a wider local context, and the cumulative future emissions likely to be generated within that context were compared with national carbon budgets.

The judgment described as “crucial scientific fact” that carbon emissions have no geographical boundary, such that their impact is not confined to the local area but felt uniformly across the globe. As such it was deemed reasonable that the only meaningful comparator for the cumulative effects of carbon emissions from the proposed schemes was the national carbon budgets. The court also relied on relevant guidance warning that “effects of GHG emissions from specific cumulative projects… in general should not be individually assessed, as there is no basis for selecting any particular… cumulative project that has GHG emissions over any other.”

In a strongly worded judgment, the Court of Appeal stated that there was “an air of complete unreality to the complaint that the SoS was somehow at fault in not having conducted a separate and wider assessment of cumulative emissions from each scheme… There is no logical basis upon which any such wider exercise could have been founded, and the inevitably arbitrary choice of the other sources of carbon emissions to be considered would only have given a spurious impression of precision to the resulting assessment.”

The challenge failed because the SoS did consider the issue of cumulative emissions and concluded that the likely future emissions fell below the threshold of significance, and that there was no meaningful way to carry out a wider assessment of cumulative emissions in the context of current scientific knowledge and the lack of any geographical boundary for such emissions. These were all issues of fact and evaluation for the decision maker, and there was nothing to indicate irrationality.


There have been a number of recent challenges raising similar issues concerning cumulative assessment of emissions. This robust judgment from the Court of Appeal appears to have clarified the position for now, at least on the basis of current scientific knowledge. It emphasises again that the policy considerations relating to climate change are not matters for the courts to consider in judicial review applications. Ultimately it is for the Government to ensure appropriate progress towards the net zero target and along the way the courts can only ensure that such issues have been considered, and that reasoned, rational and lawful conclusions are reached.

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