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Higher Than Expected Levels of Methane in California

New research from Lawrence Berkeley National Laboratory (Berkeley Lab) has found that levels of methane—a potent greenhouse gas emitted from many man-made sources, such as coal mines, landfills and livestock ranches—are at least one-and-a-half times higher in California than previously estimated.

Working with scientists from the National Oceanic and Atmospheric Administration (NOAA) Berkeley Lab scientists Marc L. Fischer and Seongeun Jeong combined highly accurate methane measurements from a tower with model predictions of expected methane signals to revise estimated methane emissions from central California. They found that annually averaged methane emissions in California were 1.5 to 1.8 times greater than previous estimates, depending on the spatial distribution of the methane emissions.

At those levels, methane would account for 9 percent of the state’s greenhouse gas emissions, compared to the current estimate of 6 percent. Their findings were published in a paper titled “Seasonal variation of CH4emissions from Central California” in theJournal of Geophysical Research.

Both the research findings as well as the methodology will have important implications for policymakers as the state strives to reduce its emissions. Under a law known as AB 32 California has a mandate to reduce greenhouse gas emissions to 1990 levels by 2020.  However, until now there has not been a good method of estimating methane emissions.

“Direct greenhouse gas emission measurements will be crucial to a sound energy and environment policy,” Fischer said. “This paper lays out a scientific method for evaluating future reductions in emissions that could be used to evaluate the success of mitigation activities at a large scale.”

Methane is a relatively potent but short-lived greenhouse gas (with a 10-year atmospheric lifetime), which traps about 70 times more heat than carbon dioxide per unit mass when averaged over a 20-year timescale. In contrast, carbon dioxide, the most abundant greenhouse gas, stays in the atmosphere for about 100 years. Black carbon (soot) is the other major short-lived climate pollutant.

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