Decadal decrease in Los Angeles methane emissions is much smaller than bottom-up estimates.

Area of Science:

• Atmospheric Science
• Climate Change Research
• Environmental Monitoring

Background:

• Methane is a potent greenhouse gas with a short atmospheric lifetime, making emissions reductions impactful for climate forcing.
• Natural gas leakage is a significant methane source in megacities like Los Angeles.
• Quantifying fugitive natural gas emissions is crucial for verifying emission reduction targets.

Purpose of the Study:

• To quantify methane emission trends in the Los Angeles area from 2011-2020.
• To compare top-down (remote sensing) and bottom-up (utility calculations) estimates of methane emissions.
• To assess the effectiveness of emission reduction strategies in a major urban area.

Main Methods:

• Utilized atmospheric remote sensing data to monitor methane concentrations.
• Analyzed emission trends over a decade (2011-2020).
• Compared satellite-derived emission data with natural gas utility reported data.

Main Results:

• Los Angeles area methane emissions showed a decreasing trend of (-1.57 ± 0.41)%/yr from 2011-2020.
• This top-down trend contrasts with the observed global increase in methane emissions.
• A significant discrepancy exists between the measured emission reduction rate and the much larger negative trend reported by the natural gas utility (-5.8%/yr).

Conclusions:

• Top-down measurements reveal a moderate decrease in LA's methane emissions, suggesting some success in reduction efforts.
• The disparity between top-down and bottom-up trends underscores uncertainties in emission estimation and reporting.
• LA's experience provides a potential model for other cities and international efforts, such as COP28, aiming to curb methane emissions.