Atmospheric Observation-based Evaluation of Fossil Fuel CO2 Emissions in London

Governments, companies and private citizens are taking actions to reduce greenhouse gas emissions and climate change. In the UK, official policies are being developed following the 2008 Climate Change Act and the 2021 Net Zero Strategy. The largest contributor to climate change by far is the burning of fossil fuels, which emits carbon dioxide (CO2) to the atmosphere. The way that fossil fuel CO2 emissions are quantified is by counting up the activities that emit CO2 and multiplying that by how much CO2 each activity produces. However, these emissions inventories can include errors that are difficult to know about without a way of checking them independently.

By measuring CO2 in the atmosphere in this project, we will deploy new techniques to check the emissions calculated by the inventory in London. Actually it is not enough to measure the concentration of CO2 because CO2 is also affected by photosynthesis and respiration, so we need to make other measurements that tell us what the effect of fossil fuels is. We measure the amount of radiocarbon (14C) because fossil fuels are so old they have lost all their 14C to radioactive decay. Therefore, by measuring decreases in the fraction of carbon that is 14C, we can quantify the fossil fuel CO2 that has been added in a region. To compare with the emissions inventory, we use a model of the winds in the atmosphere to simulate the expected amount of fossil fuel CO2 and see if that matches our observations.

In 2020, we made some preliminary measurements of 14C in CO2 in London and we were surprised to find there was much more fossil fuel CO2 than expected based on the inventories and model simulations. Since there were only a few measurements made then, we need to make more measurements around London and see if the same discrepancy is found. If so, it suggests that regularly measuring 14C in CO2 in London would allow us to estimate fossil fuel CO2 emissions independently, and to improve the calculations in the inventory.

Another thing we observed with our preliminary data was that the effect of vegetation and soils was to take up more CO2 than expected, based on a model of photosynthesis and respiration in the UK. This model uses observations of plant activity from satellites with very high resolution that can see plants in cities. If this observation also holds when more data is collected in this project, it could suggest that London is doing more to absorb extra CO2 than we thought.

This project will use state-of-the-art techniques for atmospheric measurement and modelling to evaluate fossil fuel CO2 emissions in London. The outcomes will provide a critical new understanding of how we are contributing to climate change and help us to make better plans to reduce these contributions. We will share the project outcomes with government and the public by working with the media and through outreach activities.