Can natural gas help us reduce climate change by acting as a bridge fuel away from coal? New research from Berkeley suggests that it can, even if it modestly delays the date at which we switch to renewables.

The U.S. is in the midst of a natural gas boom. The combination of horizontal drilling and hydraulic fracturing has caused gas prices to tumble, resulting in a significant shake-up of the U.S. energy mix. Over the past 7 years U.S. CO2 emissions from electricity generation have fallen an impressive 17%, driven in large part by the replacement of dirty coal-fired generation by cleaner natural gas.

Natural gas has two major benefits over coal: it has less carbon emissions per unit of chemical energy, and can be converted into electricity at a higher efficiency (less energy is lost as waste heat). These two combined mean that the CO2 emissions from new natural gas power plants can be as little as one third of the emissions of existing coal plants.

However, natural gas also has a large potential downside: if it is leaks out before your burn it, the 100-year average climate effect of that leaked methane is about 12 times worse for the climate than the effect of CO2 from the same amount of gas if it were burned. Additionally, a large investment in gas could potentially delay the date at which we switch to a near-zero-carbon technology compared to a world where we stuck with coal for longer. On the flip side, gas makes it easier to have a large amount of intermittent renewables on the electric grid without causing disruption.

A new paper from Berkeley Earth looks in depth at how different gas leakage rates, generation efficiencies, and potential delays in zero-carbon alternatives impact the viability of gas as a bridge fuel.

As author Zeke Hausfather explains, “If we replaced current coal generation with new natural gas power plants today, and leakage rates end up being the EPA’s current best estimate, we could use that natural gas for 2.4 years for every year of coal that it replaces before breaking even on warming over the next 100 years.”

“If you compare a coal plant used for 10 years and replaced by renewables to a gas plant used for 24 years and replaced by renewables, you get the same amount of warming. This means that you could end up delaying renewables by quite a bit before the climate benefit of using gas as a bridge fuel is eliminated.”

The results are somewhat sensitive to natural gas leakage rates, which are currently highly uncertain; while the EPA estimates leakage of slightly below 2% of total production, others have found that leakage rates might be as much as 4% or above. However, the paper finds that it would take a leakage rate of 10% to make new gas worse than existing coal if both are used over the next 100 years and renewables are not delayed; for a shorter 30-year gas bridge, a leakage rate of over 13% would be required. This is because the methane has only an 8.6-year half-life in the atmosphere, and breaks down relatively quickly once gas stops being used. If renewables are delayed, the allowable leakage rate is lower.

“Natural gas is still a fossil fuel, and cannot be a long-term solution if the U.S. is to aggressively reduce greenhouse emissions,” Hausfather warns. “A gas bridge would likely have to last less than 30 years, and strong efforts would have to be made to ensure that natural gas leakage rates are kept low. Cheap natural gas can also compete with renewables, and there is an important role for renewable portfolio standards and other government programs to promote the adoption of near-zero-carbon technologies.”

“This research suggests that using natural gas as a bridge fuel away from coal is viable if we cannot immediately transition to near-zero carbon technologies. Coal is responsible for the bulk of U.S. CO2 emissions from electricity generation, and gas provides a practical way to reduce such emissions, even when we include the effects of fugitive methane.”

Paper:
Bounding the Climate Viability of Natural Gas as a Bridge Fuel to Displace Coal, by Zeke Hausfather is published in the journal Energy Policy.

http://authors.elsevier.com/a/1RQ2~14YGgMDsF

Images:
https://www.dropbox.com/sh/y4t77mbm4eagz1b/AACu3uYi5Fvuz9GWD6fBiZvma?dl=0

Contacts:
Zeke Hausfather – zeke@berkeleyearth.org, 917-520-9601
Berkeley Earth; Energy and Resources Group, U.C. Berkeley