A new report published in the journal Nature Climate Change explores technological, policy, and social changes that would need to take place in the near future in order to keep the global average temperature from rising above 2°C, a target supported by more than 190 countries as a global limit to avoid dangerous climate change. The authors show that the 2°C target could still be reached even if greenhouse gas emissions are not reduced before 2020, but only at very high cost, with higher climate risks, and under exceedingly optimistic assumptions about future technologies. This study from ETH Zurich, IIASA, and NCAR comprehensively quantifies the costs and risks of greenhouse gas emissions surpassing critical thresholds by 2020.
This paper presents a systematic scenario analysis of how different levels of short-term 2020 emissions would impact the technological and economic feasibility of achieving the 2 °C target in the long term. We find that although a relatively wide range of emissions in 2020—from 41 to 55 billion tons of carbon dioxide equivalent (Gt CO2e yr−1)—may preserve the option of meeting a 2 °C target, the size of this ‘feasibility window’ strongly depends on the prospects of key energy technologies, and in particular on the effectiveness of efficiency measures to limit the growth of energy demand. A shortfall of critical technologies—either for technological or socio-political reasons—would narrow the feasibility window, if not close it entirely. Targeting lower 2020 emissions levels of 41–47 Gt CO2e yr−1 would allow the 2 °C target to be achieved under a wide range of assumptions, and thus help to hedge against the risks of long-term uncertainties.
Rogelj, J., McCollum, D.L., O’Neill, B.C., Riahi, K. 2020 emissions levels required to limit warming to below 2 °C. Nature Climate Change, 2012; DOI: 10.1038/NCLIMATE1758
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