Sep 24, 2014
Switching from coal to gas may not cut carbon emissions
Switching US electricity generation from coal- to natural gas-fired power stations would not significantly lower greenhouse gas emissions, researchers have found, despite gas plants’ lower emissions per unit of electricity generated. That’s chiefly because the shift would delay the deployment and cost-competitiveness of renewable electricity technologies for making electricity.
"This was true across a variety of climate policies, and even if none of the gas leaked into the atmosphere during production," Christine Shearer of the University of California, Irvine told environmentalresearchweb. "We also found that, without a climate policy, abundant gas increased overall electricity use."
Coal-fired power stations currently supply just over 40% of electricity in the US. The nation’s Environmental Protection Agency has proposed rules that rely heavily on the substitution of natural gas for coal to lower carbon emissions by 2030. Natural gas-fired power plants emit nearly 60% less carbon dioxide per kilowatt-hour of electricity than coal-fired plants, and domestic supplies of gas have increased with the advent of hydraulic fracturing technology.
"Much of the recent discussion around natural gas has focused on the question: how much methane leaks during natural gas production, and at what rate [of leakage] does gas lose its climate benefits to coal?" Shearer said. "But we found increased gas use does not significantly lower greenhouse gas emissions because it boosts electricity consumption and slows the use of low-carbon electricity sources. We could therefore stop all leakage of methane into the atmosphere, and gas would not do much to lower emissions. What lowered emissions in our results was a price or limit on carbon emissions, not the amount of natural gas."
In the absence of any new climate policies, and for a methane leakage (fugitive emissions) rate of 1.5%, cumulative emissions for 2013 to 2055 were just 2% lower for a high gas-use scenario compared to one with low gas take-up, the team found. Setting the leakage rate to zero did not change this result substantially.
"Cutting greenhouse gas emissions by burning natural gas is like dieting by eating reduced-fat cookies," said Steven Davis, also of the University of California, Irvine. "It may be better than eating full-fat cookies, but if you really want to lose weight, you probably need to avoid cookies altogether."
Shearer, Davis and colleagues John Bistline from Stanford University, and Mason Inman from US non-profit Near Zero analysed the power sector for scenarios with no climate policy, a moderate carbon tax ($25 per ton of carbon dioxide in 2013) and a strict carbon cap that reduces carbon dioxide emissions by 83% in 2050 relative to 2005 levels. The researchers also looked at the effects of a federal renewable portfolio standard (RPS) that requires use of more renewable electricity such as on- and offshore wind, photovoltaics and concentrated solar power.
"Natural gas has been presented as a bridge to a low-carbon future, but what we see is that it's actually a major detour," said Shearer. "We find that the only effective paths to reducing greenhouse gases are a regulatory cap or a carbon tax."
Without such climate policies, more abundant natural gas may actually slow the process of decarbonization by delaying deployment of renewables, the researchers believe. In the study, using more gas reduced the use of both coal and renewable energy.
"This effect of abundant gas on renewable energy is dampened by a price or cap on carbon but still holds, as there is less renewable energy across all climate policies," wrote the team in Environmental Research Letters (ERL). "Only the RPS resulted in similar amounts of renewable electricity use for both low and high gas supply, as the policy’s mandated renewable electricity use decreased market competition between natural gas and renewables."
To carry out the study, the team used expert elicitation to estimate natural gas supply and future production costs.
"We asked natural gas experts for their supply curve estimates, and approached our co-author John Bistline about running the responses through the energy-economic model MARKAL, to examine the effects," said Shearer.
Supply curves indicate the total natural gas available as a function of the wellhead price, while the MARKAL model picks the energy technologies that will meet projected US demand at the lowest cost up to 2055.
About the author
Liz Kalaugher is editor of environmentalresearchweb