Led by Katsumasa Tanaka, a top climate risk researcher at the National Institute for Environmental Studies in Japan, the study examined global circumstances for transitioning from coal to gas using a novel approach that applied metrics developed for climate impact assessments to the coal-gas controversy the first time. Working on the world's main power generators — China, Germany, India, and the United States — the study evaluated the impacts from many different direct and indirect emissions of such a shift on both shorter and longer timescales covering for a few decades to a century.
 
'Many previous studies were somewhat ambivalent about the climate benefits of the coal-to-gas shift,' said Tanaka. 'Our study makes a stronger case for the climate benefits that would result from this energy transition, because we carefully chose metrics to evaluate the climate impacts in light of recent advances in understanding metrics.'
 
'Given the current political situation, we deliver a much-needed message to help facilitate the energy shift away from coal under the Paris Agreement,' Tanaka said. 'However, natural gas just isn't an end goal; we consider it as a bridge fuel on the road to more eco friendly forms of energy in the long run as we move toward decarbonization.'
 
Issues about methane leakage from natural gas have been seriously argued, in particular in the United States given the increasing use of fracking over the past decade. Recent scientific efforts have advanced understanding of the degree of methane leakage in the United States, but the possible affects of methane leakage continue highly uncertain in the rest of the world.
 
'Our conclusion that the benefits of natural gas outweigh the possible risks is robust under a broad range of methane leakage, and under uncertainties in emissions data and metrics,' Tanaka said.
 
This research was partially supported by the Environment Research and Technology Development Fund (2-1702) of the Environmental Restoration and Conservation Agency in Japan, with additional support from the Institute for Advanced Sustainability Studies in Germany and the Research Council of Norway.
 
Multiple Metrics to Simultaneously Examine Short- and Long-Term Climate Impacts
 
Emissions metrics, or indicators to evaluate the impacts to climate vary from different emission types, are useful tools to gain insights into climate impacts without the need for climate model runs.
 
These metrics work similarly to weighting factors when calculating CO2-equivalent emissions from the emissions of a variety of greenhouse gases. In spite of this, the resulting climate impacts observed through CO2-equivalent emissions are sensitive to the specific metrics chosen.
 
'Because the outcome can strongly depend on which metrics are chosen and applied, there is a need for careful reflection about the meaning and implications of each specific choice,' said Francesco Cherubini, a professor at the Norwegian University of Science and Technology. 'Each emission type elicits a different climate system response. The diverging outcomes in previous studies may well stem from the type of metric that was chosen.'
 
The study joined together a number of metrics to address both short- and long-term climate impacts in parallel. It was uncovered that natural gas power plants have both smaller short- and long-term impacts than coal power plants, even when high potential methane leakage rates, a full array of greenhouse gases and air pollutants, or uncertainty issues are considered.
 
Regional Differences
 
To ensure that possible regional disparities were taken into account in the global study, the study compared global metrics with regional metrics to more precisely examine impacts.
 
'We considered a suite of so-called short-lived climate pollutants (SLCPs), such as SOx, NOx, and black carbon, that can be emitted from these plants,' said Bill Collins, a professor at the University of Reading, in the United Kingdom. 'This required a regional analysis because climate impacts from SLCPs depend on where they are emitted, due to their short lifetimes in the atmosphere.'
 
Future Directions and Policy Relevance
 
The study by Tanaka and coauthors is part of an emerging body of literature that reaffirms the need to phase out coal to be able to reduce rising global temperatures and slow or reverse negative impacts of climate change.
 
Future related work could think about supply chains and trade within and across nations and other environmental factors, in addition to work on maximizing the consistency of metrics for comparing climate impacts.
 
'Air quality is not part of our analysis, but including it would likely strengthen our conclusion,' said Tanaka. Other environmental effects, such as drinking water contamination and induced seismic activities, could also add important dimensions to the debate.'
 
This article is originally posted on tronserve.com