The climate impacts of methane emissions
What will it take to get sustained benefits from natural gas?
There has been much debate about the climate implications of increased natural gas usage. While it is true natural gas burns cleaner than other fossil fuels, methane leaking during the production, delivery and use of natural gas has the potential to undo much of the greenhouse gas benefits we think we're getting when natural gas is substituted for other fuels.
Methane, the primary component of natural gas, is a powerful, short-lived greenhouse gas. It is more than 100 times more potent at trapping energy than carbon dioxide (CO2), the principal contributor to man-made climate change. When considering its conversion to carbon dioxide over time its impact on an integrated weight basis is 84 times more potent after 20 years and 28 times more potent after 100 years.
The problem starts when unburned gas gets into the atmosphere. Leaks and releases occur throughout the natural gas supply chain, but no one is sure exactly where the leaks and releases are or how much escapes. If not better mitigated, methane leaks and releases could undermine the greenhouse gas advantage natural gas offers and spell major trouble for the climate.
The good news is that leaks can be detected, measured and reduced.
Methane leakage study
EDF and its partners recently completed an ambitious scientific research effort in order to find and measure the leaks and releases across the U.S. natural gas supply chain. The 16-part project involved more than 100 academic researchers and natural gas industry companies. It found that methane emmisions from U.S. onshore oil and gas operations are 60% higher than official estimates suggest.
Findings from this effort help inform policymakers, researchers and industry, providing new insights and data about the sources of methane emissions from across the natural gas supply chain and illuminating ways to reduce those emissions.
Methane leakage paper
The 2012 scientific paper illustrates the importance of accounting for methane leakage across the value chain of natural gas when considering fuel-switching scenarios from gasoline, diesel fuel and coal to natural gas. Published in Proceedings of the National Academy of Sciences (PNAS), the paper was co-authored by EDF scientists Ramon Alvarez and Steve Hamburg with Stephen Pacala, James Winebrake and William Chameides.
Key findings of the PNAS paper, based on the best available estimates on methane emissions from the EPA in 2012, include:
- Assuming the Environmental Protection Agency's (EPA) 2009 leakage rate of 2.4% (from well to city), new natural gas combined cycle power plants reduce climate impacts compared to new coal plants; this case is true as long as leakage remains under 3.2%.*
- Assuming EPA's estimates for leak rates, compressed natural gas (CNG)-fueled vehicles are not a viable mitigation strategy for climate change because of methane leakage from natural gas production, delivery infrastructure and from the vehicles themselves. For light-duty CNG cars to become a viable short-term climate strategy, methane leakage would need to be kept below 1.6% of total natural gas produced (approximately half the current amount for well to wheels – note difference from well to city).
- Methane emissions would need to be cut by more than two-thirds to immediately produce climate benefits in heavy duty natural gas-powered trucks.
- At current leakage rate estimates, converting a fleet of heavy duty diesel vehicles to natural gas would result in nearly 300 years of climate damage before any benefits were achieved.
Methane leakage model
Our economics team has created a methane leakage model based on the science in the 2012 PNAS paper. The model explores the climate implications of reducing emissions from natural gas systems in the context of a switch towards natural gas-fueled technologies.
To use the model, enter a policy case of desired values for natural gas leak rates and sector fuel mixes. Power plant efficiencies can also be modified. The model outputs a graph and summary table of the impact of that policy case on the climate. Results are represented as a percentage change in net radiative forcing relative to 2010 U.S. emissions.
*EDF calculation based on IPCC AR4 values for radiative efficiency and atmospheric lifetimes of CH4 and CO2