Are national HFC emissions reports suitable for global policy negotiation?

Negotiations are underway to determine whether the use of hydrofluorocarbons (HFCs) should be regulated under the Montreal Protocol, the international treaty that is designed to protect the stratospheric ozone layer. Whilst HFCs do not deplete stratospheric ozone, they are potent greenhouse gases (GHG), with global warming potentials hundreds to thousands of times that of carbon dioxide. Therefore, proponents of the proposed amendments to the Protocol argue that, because their rapid growth in the atmosphere is a direct result of the global phase-down of ozone depleting substances, for which HFCs are replacements, their resulting impact on global climate should now be regulated under the same framework. A major limitation of the on-going discussions is that emissions of HFCs are very poorly constrained at present, with more than 60% of the global emissions, as determined using atmospheric measurements, being un-reported in 2012. This could be due to poor reporting practices, and/or the incomplete nature of global emissions reports under the United Nations Framework Convention on Climate Change (UNFCCC), in which only a subset of countries are required to report their emissions in detail. Recent estimates of the emissions of HFCs and other synthetic GHGs derived from atmospheric measurements indicate that both factors are likely to contribute. However, a comprehensive evaluation of such "top-down" emissions estimates for the major reporting countries has not yet been carried out. Furthermore, we argue that the uncertainty quantification methods in the "inverse" modelling frameworks that are used to derive emissions of HFCs (and all other GHGs) must be dramatically improved if they are to be robust and relevant to policy makers.

This proposal aims to develop new methods for estimating national GHG emissions using atmospheric observations and chemical transport models. In particular, we will pioneer the use of hierarchical Bayesian modelling and Gaussian process emulation. These techniques will allow us, for the first time, to explicitly include the influence of some critical uncertainties in the atmospheric modelling process on "top-down" emissions estimates. This will allow us to estimate national emissions of the major HFCs with a more complete estimate of the uncertainty than has previously been possible. We will examine in detail the differences between these emissions estimates and the national inventories, and determine critically whether the current reports submitted to the UNFCCC are appropriate for informing the debate on the future of the Montreal Protocol.

Emissions of hydrofluorocarbons (HFCs) are the subject of intense interest at present, due to on-going negotiations that aim to decide whether their use should be limited under the Montreal Protocol due to their potential to contribute significantly to global warming. Furthermore, there are growing concerns that estimates of the emissions of these substances, which are reported to the United Nations Framework Convention on Climate Change (UNFCCC) by "developed" countries, may be subject to inaccuracies or omissions. Therefore, the impacts of this proposal are targeted towards on researchers and agencies responsible for estimating HFC emissions, climate scientists and the general public, with the central aim of improving the information available for policy negotiation.

This proposal aims to quantify HFC emissions for the major reporting countries using atmospheric measurements, with a comprehensive evaluation of the uncertainty budget in such estimates. This information will be invaluable to agencies responsible for compiling national emissions inventories, as it will provide a robust, independent evaluation. It will also be useful to government departments and policy makers who are required to evaluate the success of emissions reduction schemes, and who must participate in international treaty negotiation, such as the on-going discussions surrounding the Montreal Protocol. In the UK, the primary beneficiary will be the Department for Energy and Climate Change (DECC), which is responsible for the UK's emissions reports. DECC have demonstrated their interest in this field, in particular, by funding a network of GHG monitoring sites in the UK, which will be used in this proposal.

In the UK and internationally, we will engage with a network of researchers who are responsible for estimating national GHG emissions. This particularly includes researchers in Switzerland and Australia, who, together with the UK, are the only countries to currently report "top-down" emissions estimates to the UNFCCC in addition to the more widely used "bottom-up" accounting methodologies. We will also engage with project partners in countries such as the USA and South Korea. Despite not producing detailed top-wodn emissions reports, these researchers, and the agencies that fund them, have a keen interest in developments that are being made in countries such as the UK, which will influence their future reporting plans.

It has recently been shown that HFCs could have a substantial impact on global climate in the coming decades. Therefore, HFC emissions must be of concern to the wider academic community interested in climate change. Furthermore, there is a high level of public concern regarding climate change and greenhouse gases.

A detailed engagement plan with these beneficiaries is outlined in the Pathways to Impact. The central strategy involves further strengthening the close ties that the team has with DECC and international researchers involved in the Advanced Global Atmospheric Gases Experiment (AGAGE). The outcomes of this research will be disseminated to these beneficiaries through workshops, meetings, and sharing of code and emissions estimates. We will engage with the wider research community and the general public through regular publications, attendance at general climate science conferences, and regular use of public outreach opportunities such as those organised through the University of Bristol's Cabot Institute.