UK Climate Change Act and actual Greenhouse Gas emissions

by Carl Edward Rasmussen, 2021-03-28

The UK has a strong ambition to reduce greenhouse gas emissions. In this short note, the government's ambition is compared to the actual greenhouse gas emissions. It is great that the UK government have set concrete targets rather than just some vague intensions, so one can debate whether they are appropriate and check whether the targets are actually being met. Finding a good source of information is not trivial for a variety of reasons: some sources use tons of carbon, others tons of carbon dioxide, some targets are for five year intervals others are annual, and some targets are given as a percentage of other emissions, which may themselves be difficult to find.

The Climate Change Act 2008 sets legal limits on the greenhouse gas emissions for the UK and specifies a reduction of greenhouse gases by 2050 of 80% relative to the emissions in the year 1990, and was later amended to 100% reduction by 2050. For this purpose, greenhouse gases are quantified in terms of Million Tons of CO2 equivalents, or MtCO2e. There are several different gases which contribute to the greenhouse effect, each with different potencies and different concentrations. Carbon dioxide has the largest effect (apart from water vapour, which can't easily be manipulated), and it is customary to translate other greenhouse gases into equivalent amounts of carbon dioxide.

In addition to the goal in 2050, the act also specifies some intermediate targets for the cumulative emissions in 5 year intervals. The first 5 year interval was start of 2008 until end of 2012. The target for each interval gets specified 12 years prior to the start of the interval. Currently, limits have been set for 2013-2017, 2018-2022, 2023-2027, 2028-2032 and 2033-2037 (the sixth budget (2033-2037) is currently a proposal, and hasn't yet been signed into law).

The data for the emissions are taken from these document collections, Provisional UK greenhouse gas emissions national statistics, and Final UK greenhouse gas emissions national statistics shown below:

UK Climate Change Act and actual Greenhouse Gas emissions

The UK emissions from 1990 together with the legislated limits are plotted above. The total limits for the six five year budget periods have been divided by five and plotted as constant levels over the entire period (although the requirement is only that limits hold on average).

Note that in contrast to most other plots of this data, the plot has a logarithmic axis for the emissions; this has been done so that the same relative reduction always has the same size on the plot. For example, a reduction of 100 MtCO2e would be a very different objective in 2010 when emissions were >600 MtCO2e per year than in 2035 when emissions are (hopefully) <200 MtCO2e per year. A straight line on the plot with a logarithmic axis for the emissions corresponds to the same relative (percentage) reduction every year. When we get very close to NetZero, a logarithmic emissions axis may no longer be the best representation, but that's some way off yet. Note, for representing the effort required, a logarithmic emissions axis is appropriate, but if you are strictly interested in the environmental impact, it's the total amount of CO2e which is important, in that case a linear axis is more appropriate.

A straight line from the middle of the first budget interval to the middle of the (historical) -80% goal in year 2050 has been superimposed, representing an even (relative) rate of 3.3% reduction per year. Another straight line with an even (relative) rate of 5.8% reduction per year is shown from where we were in 2019 to the middle of the sixth budget limit. Note, that the legislated limits are for emissions excluding international aviation and shipping (with the exception of the sixth proposed budget and the NDC); on the graph, both the actual emissions and the emissions with exclusions are plotted.

During both the first legislated interval 2008-2012 and the second interval 2013-2017 the emissions were below the limit set.

The concrete nature of the Climate Act and the fact that emissions are in line with the limits is great. But some aspects of the situation could be criticised: