Atmospheric methane levels in California are at least one-and-a-half times higher than researchers have previously suspected. The conclusion belongs to a new study conducted by experts at the US Department of Energy's (DOE) Lawrence Berkeley National Laboratory (Berkeley Lab).
The group analyzed methane emissions from coal mines, livestock ranches, landfills and other man-made sources, and found that previous studies significantly underestimated the amount of the potent greenhouse gas in the air above California.
On average, methane (CH4) is around 300 times more potent in heating the atmosphere than its more abundant and renowned cousin, carbon dioxide (CO2). Fortunately, it is produced in smaller amounts.
In order to ensure access to the most relevant data, the Berkeley Lab team joined forces with experts from the US National Oceanic and Atmospheric Administration (NOAA) for the new investigation.
Highly accurate methane measurements were collected by instruments on top of a 610-meter (2,000-foot) science tower in Walnut Grove. The information was combined with the conclusions of computer models estimating methane spread above the Golden State.
The work was led by Marc L. Fischer and Seongeun Jeong, who are both scientists at Berkeley Lab. Annually-averaged methane emissions over the state, they discovered, are 1.5 to 1.8 times higher than originally calculated.
The new figures indicate that methane accounts for 9 percent of California's greenhouse gas emissions, not 6 percent. Details of the work appear in the latest issue of the Journal of Geophysical Research, in a paper entitled “Seasonal variation of CH4 emissions from Central California.”
Under a law called AB 32, California needs to reduce its GHG emissions to 1990 levels within 8 years, and knowing which gas accounts for how much of the overall pollution is an important aspect of this effort.
“Direct greenhouse gas emission measurements will be crucial to a sound energy and environment policy. 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,” Fischer explains.