An emission pathway classification reflecting the Paris Agreement
climate objectives
Abstract
Since its adoption, the Paris Agreement sets and defines the global
climate ambition. The overall scope of this ambition is expressed in its
long-term temperature goal in Article 2 as well as the ‘net zero’
mitigation goal in Article 4. To provide guidance to climate policy, the
scientific community has explored the characteristics of greenhouse gas
(GHG) emission reduction pathways that can meet the Paris Agreement
goals. However, when categorizing and presenting such pathways including
in reports of the Intergovernmental Panel on Climate Change (IPCC), the
focus has been put on the temperature outcome and not on the emission
reduction criteria set out in Article 4.1. Here we propose a pathway
classification approach that aims to comprehensively reflect all climate
criteria set out in the Paris Agreement. We show how such an approach
allows for an internally consistent interpretation of the Paris
Agreement in terms of emission reduction pathways. For pathways that
simultaneously are very likely to hold warming to below 2°C, pursue
efforts to limit warming to 1.5°C and achieve the provisions outlined in
Article 4.1, we report 2030 global Kyoto-GHG emissions of between 20-26
Gt CO2eq (interquartile range), net zero CO2 emissions around 2050 and
net zero GHG emissions around 2060. We further illustrate how prevalent
pathway classifications focusing, for example, on the temperature
outcome in 2100 result in additional criteria being applied that are not
rooted in the Paris Agreement. We outline the consequences of such
approaches including for the deployment of carbon dioxide removal (CDR)
in such pathways. We find that across pathways classified as ‘no or low
overshoot’ pathways in previous IPCC reports, such non-Paris related,
additional criteria for end-of-century outcomes may lead to about 20%
higher CDR deployment compared to purely achieving the Paris Agreement
objectives in mitigation pathways.