In particular, the calibration of the carbon cycle has undergone significant changes. Because advanced climate models are too computationally intensive, TIMs use simplified models, which often consist of only a few linear equations. However, it has been shown that many TIMs cannot fully replicate the carbon cycle dynamics of complex, state-of-the-art models37,38. In particular, linear representations of the carbon cycle poorly reflect the ocean`s nonlinear response to higher atmospheric carbon levels.39 Linear representations adapted to the initial absorption of carbon lead to too rapid removal of atmospheric CO239 after several decades. The warming of the coming centuries and the scale of the political interventions needed are therefore underestimated37,38,39. This problem also exists in DICE-2013, which aims to adapt the dynamics of the small carbon cycle (mainly the first hundred years)21 larger models. The use of the DICE-2013 carbon cycle model in this study therefore means that, although the model does represent the dynamics of the carbon cycle over this century (see Figure 1 in Glotter et al.39 and the temperature evolution for the representative concentration pathways in Supplementary Figure 7), our results regarding the temperature target and optimal policy efforts are rather conservative estimates. The error in policy recommendations can become particularly important for small discount rates, which can be seen in light of our robustness test with other values of preference parameters (Fig. 5).
To recalibrate the DICE according to these SSPs, we use data (up to 2100) from the integrated energy-agriculture-economy-climate scenarios generated by the REMIND-MAgPIE56 model. REMIND-MAgPIE is one of the TIMs with a detailed description of the energy sector selected to translate SSP narratives into quantitative projections25. Due to the process of interpreting narratives and different model designs, each IAM model has alternative interpretations of SSPs. For each SSP, a different IAM was selected to generate the so-called marker scenario. For our calibration exercise, we do not rely on the simulation results of the different marker models, but on the data generated by a single model to avoid compatibility problems. So far, SSP1, SSP2 and SSP5 have been studied with REMIND. The calculated scenarios consist of reference levels in which climate policy is lacking and cycles in which mitigation efforts correspond to representative concentration pathways (RCPs). To this end, a new average SPC of 3.4 W m−2 has been developed, as it is important for research on the accessibility of the 2°C25 target. United Nations Framework Convention on Climate Change. Paris Agreement.
Article 2(a) unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement (2015). Inter-Institutional Working Group on the Social Costs of Carbon; U.S. Government. Technical Support Document: Technical Update of The Social Costs of Carbon for Regulatory Impact Analysis under Executive Order 12866 (2016). Open Access This article is licensed under a Creative Commons Attribution 4.0 International license, which allows use, publication, adaptation, distribution, and reproduction in any medium or format, provided that the original author(s) and source are properly mentioned, a link to the Creative Commons license is provided, and whether any changes have been made. Images or other third-party materials contained in this article are included in the Article`s Creative Commons License, unless otherwise specified in a line of credit for the material. If the material is not included in the creative commons license of the article and your intended use is not permitted by law or exceeds the permitted use, you must obtain permission directly from the copyright owner. A copy of this license can be found on creativecommons.org/licenses/by/4.0/. The combination of increasing exposure to climate change and the fact that there is only limited capacity to adapt to its effects amplifies the risks arising from warming of 1.5°C and 2°C. This is particularly true for developing and island States in the tropics and other vulnerable countries and territories. The risks posed by global warming of 1.5°C are greater than for current conditions, but below 2°C. But minutes after the president`s remarks, the leaders of France, Germany and Italy issued a joint statement saying the Paris climate agreement was “irreversible” and could not be renegotiated.
As part of the 2015 Paris Agreement, countries agreed to reduce greenhouse gas emissions to “keep global average temperature rise well below 2°C above pre-industrial levels and make efforts to limit temperature rise to 1.5°C above pre-industrial levels.” While the overall intention to amplify the global response to climate change is clear, the Paris Agreement does not specify exactly what is meant by “global average temperature” or what period of history should be considered “pre-industrial.” .