In 2015, the Paris Agreement was signed, committing 195 signatory nation-states to limiting greenhouse gas (GHG) emissions to well below 2 degrees Celsius above pre-industrial levels. This recognized the clear role of governments around the globe in curtailing potentially catastrophic levels of global warming, which could have widespread and systemic impacts on the global economy, capital markets, and the quality of human life. Sovereign bonds, the issuance of debt by a country to finance its activities, is one of the largest asset classes in the world, with over USD 20 trillion of central government debt securities outstanding in 2016 and general government debt exceeding USD 62 trillion in 2016. As such, it is a key mode of financing for governments, is one of the largest asset allocations by pension funds, and should be a focus of examination for climate risk analysis.
Portfolio carbon footprinting as a tool to support climate reporting and risk assessment has grown in popularity over recent years, so much so that it has become incorporated into best practice reporting guidelines for investors. These include those outlined by the Financial Stability Board’s Task Force on Climate-related Financial Disclosures (TCFD), which is backed by the central banks of the G20 countries and is legislated as part of France’s Article 173 regulation. While it is now becoming common practice for asset owners and managers to report the footprint of their listed equity holdings and corporate fixed income portfolios, sovereign bonds have remained largely unexamined from a carbon risk and reporting perspective due to lack of appropriate metrics and actionable insight. However, climate change affects all asset classes, so investors would need to measure, understand, and manage the climate change risks embedded in their sovereign bond portfolios as well.
In this paper, Trucost outlines a number of approaches to sovereign bond evaluation and the metrics available. Scope and breadth of emissions are key considerations, as is the denominator chosen to normalize emissions to facilitate comparison between entities of different size. The most appropriate metric may differ depending on the question(s) that investors intend to answer.
 World Economic Outlook Database April 2018 - International Monetary Fund, https://www.imf.org/external/pubs/ft/weo/2018/01/weodata/index.aspx.