by Louise Jeffery, NewClimate Institute
We have a paper published in Science today, with contributions from a number of CAT authors, that confirms that the latest, updated climate targets - or NDC's, if implemented, would result in a stronger near-term foundation for reaching the global warming goals of 2˚C and 1.5˚C than those pledged in 2015 ahead of the Paris Agreement.
This is a collaboration between the GCAM, CAT, and MAGICC teams providing an additional line of evidence in assessing the impact of existing climate pledges (combining CAT policy quantifications, GCAM IAM scenarios starting from those quantifications, and a corresponding MAGICC6&7 climate-based assessment).
The key finding of the paper is similar to that of CAT and many other analyses - climate ambition has increased since 2015, but not nearly enough to achieve the Paris Agreement. The increases in likelihood of achieving 1.5 or 2C are driven primarily by political action, and to a much lesser degree by changes in the latest climate science.
Critically, the study finds in modelled scenarios of current pledges that 1.5C is not 'out of reach' and that enhanced ambition significantly increases the probability of staying below 1.5C. However, further action beyond what is considered here is needed to stay below 1.5C with sufficient likelihood (>50%).
The research team brought together researchers from PNNL with researchers from the US Environmental Protection Agency, the CAT, the University of Maryland, the University of Melbourne, and Imperial College London.
Under pledges made at the 2015 Paris Agreement, the chances of limiting temperature change to below 2 and 1.5 degrees Celsius (2.7 degrees Fahrenheit) by 2100 were 8 and 0 percent, respectively.
Under the new pledges—and if those pledges are successfully fulfilled and reinforced with policies and measures of equal or greater ambition—the study’s authors estimate those chances now rise to 34 and 1.5 percent, respectively. If countries strike a more ambitious path beyond 2030, those probabilities become even more likely, rising to 60 and 11 percent, respectively.
Findings in this paper are largely consistent with other NDC analyses, including the CAT, the UNEP Gap report, and the UNFCCC report. However, this paper applies a novel methodology to arrive at these findings and gives additional perspectives.
The problem is framed as one of risk management. Previous studies have mostly assessed the outcomes of the NDCs deterministically. However, because the relationship between emissions and temperature change is inherently uncertain, the contribution of the NDCs can also be assessed in probabilistic rather than deterministic terms.
The paper also looks at most severe temperature outcomes, not only 2°C and 1.5°C: While other studies focus mostly on the implications of the NDCs for maintaining temperature change below 2°C and 1.5°C, it is also important to consider their implications for the likelihoods of higher temperature outcomes associated with larger climate impacts.
It also looks at the longitudinal strengthening of NDCs over time: We use the exact same methodology as a similar 2015 assessment (Fawcett et al., 2015), so we can compare apples-to-apples between the original pledges and the updated pledges. We find that the updated pledges further reduce 15% of the emissions, which resulted in the higher probability of staying under 2 degrees.
Finally, this study brings in the latest climate science with the climate model calibrated to the just released IPCC AR6. We find that the improved climate science doesn’t make large differences in terms of the central estimate, but we find the uncertainty range to be narrower. The updated climate science slightly increases the probability of staying under 2 degrees, but at the same time, the narrower range slightly decreases the probability of staying under 1.5 degrees.
With its analysis of different scenarios, this paper outlines the different possible futures that lie ahead - and what can and needs to be done to increase the likelihood of limiting warming to 1.5C.
The CAT authors for the paper are:
Claire Fyson, Matthew Gidden, and Andreas Geiges (Climate Analytics)
Sofia Gonzales-Zuñiga, Niklas Höhne, Louise Jeffery, and Takeshi Kuramochi (NewClimate Institute)