Applications of a joint CO2 and CH4 climate debt metric: Insights into global patterns and mitigation priorities

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The capacity for the concept of climate debt to inform the response to climate change has been underappreciated. International Natural Debt (IND) is a measure of accountability for climate change that straightforwardly and transparently attributes radiative forcing from extant emissions of the two most significant climate active pollutants (CAPs) – carbon dioxide from fossil fuels and methane – to individual entities such as countries or sectors. Here, we demonstrate how the IND metric readily operationalizes climate debt for a diversity of purposes. We characterize the vast range spanned by the global distribution of IND in total and per capita terms. Then, in a manner akin to carbon intensity, we consider the “efficiency” with which countries have accumulated IND in their pursuit of expanding economic output and diminishing ill-health, revealing priorities and pathways for countries to more effectively convert their future climate debt into income and/or health gains. Next, we forecast the IND consequences from countries achieving the ambitious goal of decreasing their CAP emissions to 80% of 1990 levels by 2050, exposing how the composition of IND, determined by the magnitude and timing of historical emissions, constrains each country’s capacity to reduce its climate debt. Lastly, we assess the IND implications from a hypothesized rapid displacement of coal by natural gas for power generation in the United States, identifying the combination of conditions under which such a substitution tilts positive or negative in terms of IND. These applications of IND reveal how the metric can both assess climate debt in comparison to other key metrics and investigate mitigation goals and strategies through scenario exercises. Ultimately, we seek to open an intellectual terrain for climate debt analyses and invite more participatory and inclusive discussions about the consequent political and economic implications of such a multiple CAP and accountability-based perspective.