Avoiding overshoot: why and how

Policy Brief #30, October 2021. Overshooting global temperature goals is risky. New research from the ENGAGE project shows the long-term economic benefits of scenarios that avoid overshoot and points out the investments needed to make it happen.

Policy Brief #30, cover

Policy Brief #30, cover

Most existing climate scenarios focus on distant temperature goals at the end of the century. This allows them to temporarily overshoot those temperatures, with CO2 emissions that break the carbon budget in mid-century, followed by net-negative emissions to repay the deficit.

The ENGAGE project, coordinated by IIASA, has studied the implications of being more ambitious, with scenarios that balance the carbon budget at the time of reaching net-zero emissions. It has also looked at the implications of following existing Nationally Determined Contributions (NDCs) until 2030. These scenarios inform the Intergovernmental Panel on Climate Change (IPCC)’s sixth assessment report (mitigation of climate change) due to be published in March 2022.

  • 1.5°C is out of reach with existing NDCs.
  • Net-negative scenarios lead to a hazardous level of overshoot. Given a budget of 1000 Gt CO2, scenarios that rely on net-negative emissions result in mid-century peak temperatures that are up to 0.15°C higher than if the budget is met by the time of net-zero. This would mean substantially higher climate impacts and risks of reaching tipping points.
  • Investment in low-carbon power should at least double by 2030 to avoid overshoot (under a 1000 Gt budget). This is mainly in solar, wind, power grids and storage.
  • Upfront investment brings long-term economic gains. End-of-century GDP is higher in scenarios that avoid overshoot.
  • Carbon removal technologies need urgent development and deployment. Even in scenarios that avoid net-negative emissions, CO2 removal is needed to accelerate near-term mitigation and to offset emissions from hard-to-abate sectors.


The full text of this policy brief is currently under embargo pending publication in Nature Climate Change. If you would like further information about this research, please contact Keywan Riahi, Program Director, Energy, Climate and Environment Program, IIASA.


IIASA Policy Briefs report on research carried out at IIASA and have received only limited review. Views or opinions expressed herein do not necessarily represent those of the institute, its National Member Organizations, or other organizations supporting the work.


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Last edited: 27 October 2021

CONTACT DETAILS

Keywan Riahi

Program Director and Principal Research Scholar Energy, Climate, and Environment Program

Program Director and Principal Research Scholar Integrated Assessment and Climate Change Research Group - Energy, Climate, and Environment Program

Program Director and Principal Research Scholar Pollution Management Research Group - Energy, Climate, and Environment Program

Program Director and Principal Research Scholar Sustainable Service Systems Research Group - Energy, Climate, and Environment Program

T +43(0) 2236 807 491

Bas van Ruijven

Research Group Leader and Senior Research Scholar Sustainable Service Systems Research Group - Energy, Climate, and Environment Program

Senior Research Scholar Integrated Assessment and Climate Change Research Group - Energy, Climate, and Environment Program

Senior Research Scholar Transformative Institutional and Social Solutions Research Group - Energy, Climate, and Environment Program

T +43(0) 2236 807 288

PUBLICATIONS

Rogelj, J. , Huppmann, D. , Krey, V. , Riahi, K. , Clarke, L., Gidden, M. , Nicholls, Z., & Meinshausen, Malte (2019). A new scenario logic for the Paris Agreement long-term temperature goal. Nature 573 (7774), 357-363. 10.1038/s41586-019-1541-4.

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