Coal-to-gas: a bridge fuel on the way towards reduced emissions

Many previous studies are somewhat ambivalent about the climate benefits of the coal-to-gas shift. Our new study in Nature Climate Change shows that the shift may reduce climate impacts of at least 50%.

Global coal demand continues to grow (0.7% in 2018, according to IEA statistics), and coal represents the largest source of electricity in the world. Burning coal is the biggest single source of carbon dioxide emissions from human activity, and one of the major driver of climate change. Phasing out coal with natural gas (a less C intensive fuel) is one of the most cost-effective options to reduce CO₂ emissions in the near term. However, many previous studies were somewhat ambivalent about the climate benefits of the coal-to-gas shift, mainly because of potential high methane leakage rates during natural gas extraction, transport, and processing.

Methane is a very powerful greenhouse gas, and these leakages in some cases were found to offset the climate benefits of CO₂ emission reductions. Further, the consideration of emissions of so-called short-lived climate pollutants (SLCPs), such as SOx, NOx, and black carbon, that can be emitted from these plants complicate the picture, because they can affect the climate through many complex processes that vary over time and space.

A stronger case for this energy transition

Our study specifically investigated the implications for climate change of the coal-to-gas shift considering the full spectrum of emissions, possible methane leakage rates, plant locations, and up-to-date climate indicators. We came up with a stronger case than previous studies in support of the climate benefits that would result from this energy transition, for both short and long-term perspective. Other aspects not considered in our study, such as air quality, will likely strengthen the case for the coal to gas shift.

A question of metrics

Each emission of climate active species causes a different climate system response. The diverging outcomes in previous studies of the coal-to-gas shift may well stem from the metric type that was chosen as common indicator to compare the effects of different emissions on climate. Because the outcome can strongly depend on which metrics are applied, there is a need for careful reflection about the meaning and implications of each specific choice.

In our analysis, we used the metrics available from the latest IPCC report and focused on those that are most consistent with the Paris Agreement temperature goals. This choice of metrics aligned with the recent recommendations by the United Nations Environmental Programme and the Society of Environmental Toxicology and Chemistry. It is the first application of such recommendations to the coal-to-gas debate.

We found that the coal-to-gas shift is consistent with climate stabilization objectives for the next 50–100 years. Our finding is robust under a range of leakage rates and uncertainties in emissions data and metrics. Our case for the coal-to-gas shift is stronger than previously found, reinforcing the support for coal phase-out.

Gas is more efficient and easily available, but it is not an end goal

Natural gas power plants are usually more efficient than coal plants, and when appropriate measures to prevent methane leakage are in place electricity production from natural gas power plants is found to reduce climate impacts of about 50% in the short-term and up to two thirds in the long-term relative to coal power plant. The technology is ready and available to be implemented across scales, and these emission savings can help our society to get on track for emission reduction pathways. This is particularly relevant under the pursue for options to mitigate climate change and achieve quick emission reductions as expected by the national pledges under the Paris Agreement.

However, there are risks as well connected with this shift, such as the carbon lock-in from fossil fuel infrastructure, which might become problematic in the absence of commercially viable and scalable CCS, or that prioritizing this shift may delay the deployment of less carbon-intensive technologies such as renewable energy options. Proper governance and long-term vision should ensure that this shift is part of long-term decarbonization strategies based on the wide variety of energy resources and mitigation options available that are technically feasible in the present and foreseeable future.  In this context, it should be made clear that natural gas is not an end goal; we regard it as a bridge fuel until less carbon-intensive technologies, such as renewables, or carbon capture and storage become viable for large-scale implementation.

Read also: “- Gas instead of coal is 50 % better for the climate” at Gemini.no (in Norwegian)

•  The study is published in Nature Climate Change 22 April 2019
• References: Tanaka, K., Cavalett, O., Collins, W., Cherubini, F. (2019). ‘Asserting the climate benefits of the coal-to-gas shift across temporal and spatial scales’. Nature Climate Change. doi: 10.1038/s41558-019-0457-1

Blog post originally published on www.ntnutechzone.no on April 29th, 2019

Francesco Cherubini

Francesco Cherubini is a Professor at NTNU – Norwegian University of Science and Technology, at the Industrial Ecology Programme and the Department of Energy and Process Engineering.