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Climate impacts of energy technologies depend on emissions timing

An Erratum to this article was published on 28 May 2014

This article has been updated


Energy technologies emit greenhouse gases with differing radiative efficiencies and atmospheric lifetimes1,2,3. Standard practice for evaluating technologies, which uses the global warming potential (GWP) to compare the integrated radiative forcing of emitted gases over a fixed time horizon4, does not acknowledge the importance of a changing background climate relative to climate change mitigation targets5,6. Here we demonstrate that the GWP misvalues the impact of CH4-emitting technologies as mid-century approaches, and we propose a new class of metrics to evaluate technologies based on their time of use. The instantaneous climate impact (ICI) compares gases in an expected radiative forcing stabilization year, and the cumulative climate impact (CCI) compares their time-integrated radiative forcing up to a stabilization year. Using these dynamic metrics, we quantify the climate impacts of technologies and show that high-CH4-emitting energy sources become less advantageous over time. The impact of natural gas for transportation, with CH4 leakage, exceeds that of gasoline within 1–2 decades for a commonly cited 3 W m2 stabilization target. The impact of algae biodiesel overtakes that of corn ethanol within 2–3 decades, where algae co-products are used to produce biogas and corn co-products are used for animal feed. The proposed metrics capture the changing importance of CH4 emissions as a climate threshold is approached, thereby addressing a major shortcoming of the GWP for technology evaluation7,8.

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Figure 1: Comparisons of greenhouse gases and technologies depend on the evaluation horizon.
Figure 2: GWP(100) underestimates the radiative forcing contribution of CH4-emitting technologies.
Figure 3: Metric development.
Figure 4: Technology comparisons.
Figure 5: Simulations of radiative forcing and vehicle kilometres travelled.

Change history

  • 25 April 2014

    In the print version of this Letter, the y axes in Fig. 4a,b should have been labelled 'Impact (g CO2-eq km-1)'. In addition, the first sentence of the author contributions should have read 'J.E.T. developed the concept and designed the methods for the study.' These errors have been corrected in the HTML and PDF versions of the Letter.


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The authors thank J. McNerney for his contributions to the development of the metric testing model. We thank S. Solomon for helpful feedback on this manuscript. This research was partially financially supported by the New England University Transportation Center at MIT under DOT grant No. DTRT07-G-0001.

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J.E.T. developed the concept and designed the methods for the study, M.R.E. and J.E.T. performed the analysis, J.E.T. and M.R.E. wrote the paper.

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Correspondence to Jessika E. Trancik.

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The authors declare no competing financial interests.

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Edwards, M., Trancik, J. Climate impacts of energy technologies depend on emissions timing. Nature Clim Change 4, 347–352 (2014).

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