Conceptualising the Paris Agreement long-term temperature goal
The central objective of the Paris Agreement is its long-term temperature goal to hold global average temperature increase to “well below 2°C above preindustrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels”. This goal is linked to a requirement in the Paris Agreement1 that all countries work together to bring greenhouse gas emissions to zero within the second half of the 21st century, with the timing of when the zero emissions are reached being determined by the best available science in relation to the achievement of the long-term temperature goal. The long-term temperature goal in the Paris Agreement goes significantly further, both legally and substantively, than the earlier goal to hold warming to below 2°C (Schleussner et al. 2016).
The Copenhagen Accord from 2009 mentions the long-term temperature goal of holding the global temperature increase to “below 2 degrees Celsius” (UNFCCC 2010). One year later, Parties to the UNFCCC adopted the Cancun Agreements which “further recognised that deep cuts in global GHG emissions are required, with a view to hold the increase in global average temperature below 2°C above preindustrial levels”.
Because of disquiet amongst the vulnerable countries about the adverse consequences ultimately of a 2°C warming level at the same time the UNFCCC established a process to review whether the long-term temperature goal of holding warming below 2°C was adequate to avoid dangerous climate change and to consider “strengthening the long-term global goal on the basis of the best available scientific knowledge, including in relation to a global average temperature rise of 1.5°C”. 2 This process ended in 2015 with the final report of its scientific arm (Structured Expert Dialogue) concluding that using the globally-agreed warming limit of 2°C as a “guardrail” is not safe, and that governments should aim for 1.5°C instead3. The 2°C limit was found not to be in line with the ultimate objective of the Convention to “prevent dangerous anthropogenic interference with the climate system.”
Over the years, there has been a strong consensus within the scientific community in interpreting the Cancun Agreements’ goal of holding warming below 2°C with the “likely below” 2°C class of scenarios. These energy-economic model pathways have a 66% chance, or greater, of staying below a 2°C global mean warming above pre-industrial levels throughout the 21st century. The Climate Action Tracker has used those pathways as benchmark for emissions reductions in line with 2°C, as well as a basis for assessing the adequacy of efforts of individual countries.
From its inception in 2009 the Climate Action Tracker itself has consistently referred to the 1.5°C global mean warming limit in its analyses, alongside the 2°C pathway, particularly in relation to comparing the global effect of pledges and commitments with emission pathways for both these warming limits. However, given the lack of scenarios with appropriate resolution for 1.5°C pathways the rating system of the Climate Action Tracker has drawn mainly from the published 2°C pathways and related equity and fairness studies.
The Paris Agreement goes beyond the Cancun Agreements’ below 2°C limit and aims to hold warming to well below 2°C and to pursue efforts to limit temperature increase to 1.5°C. There are currently two interpretations of the implications:
- In one interpretation, warming might exceed the 1.5°C level by a small amount while remaining “well below 2°C” returning to 1.5°C
- Another interpretation, held by most vulnerable countries, is that the Paris Agreement warming should not exceed 1.5°C.
Schleussner, C.-F. et al., 2016. Science and policy characteristics of the Paris Agreement temperature goal. Nature Climate Change, 6(9), pp.827–835. Available at: http://www.nature.com/doifinder/10.1038/nclimate3096.
UNFCCC, 2010. Report of the Conference of the Parties on its fifteenth session, held in Copenhagen from 7 to 19 December 2009. In Copenhagen.