Assessing negative carbon dioxide emissions from the perspective of a national 'fair share' of the remaining global carbon budget

摘要

We present an assessment of the plausible Paris-alignedfair sharenett cumulative carbon dioxide (CO2) quota for an example nation state, the Republic of Ireland. ByParis-aligned, we mean consistent with the Paris Agreement adopted at the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change, at Paris, France, in December 2015 (UNFCCC2015). We compare and contrast this quota with both the aspirations expressed in the current IrishNational Policy Positionand current national emission projections. The fair share quota is assessed as a maximum of c. 391 million tonnes of carbon dioxide (MtCO(2)), equal to 83 tonnes of carbon dioxide (tCO(2)) per capita, from 2015, based on a precautionary estimate of the global carbon budget (GCB) and specific interpretation of global equity. Given Ireland's high current CO(2)per capita emission rate, this would correspond to sustained year-on-year reductions in nett annual CO(2)emissions of over - 11% per year (beginning as of 2016). By contrast, the CO(2)mitigation target indicated in the National Policy Position corresponds to nett annual reduction rates in the range of only -4.7% per year (low ambition) up to a maximum of - 8.3% per year (high ambition), and projections based on current and immediately planned mitigation measures indicate the possibility, instead, of sustainedincreasesin emissions at a rate of the order of + 0.7% per year. Accordingly, there is a large gap between Paris-aligned ambition and current political and policy reality on the ground, with a significant risk of early emergence of "CO(2)debt" and tacit reliance on rapid deployment of currently speculative (at a relevant scale and feasible cost) negative CO(2)emission technologies to actively remove CO(2)from the atmosphere. While the detailed policy situation will clearly differ from country to country, we suggest that this methodology, and itsCO(2)debtframing, may be usefully applied in other individual countries or regions. We recommend that such framing be incorporated explicitly into a global mitigation strategy via the statements of nationally determined contributions required to be submitted and updated by all parties under the Paris Agreement processes.