Emissions from California's transportation sector increased 6 percent from 2013 to 2017 (or 9 million metric tons of carbon dioxide-equivalent), while overall emissions in the state decreased by 5 MMTCO2-e from 2016 to 2017, according to the California Air Resources Board's latest emissions report.
Transportation emissions have increased due to population growth, lower fuel prices, more consumer and economic activity, and higher overall employment, and dropped most significantly during the Great Recession years from 2009 to 2012, according to the report published last week.
The electricity sector accounted for much of the state's overall emissions decrease, falling 9 percent in 2017 compared with 2016, as more zero-carbon and renewable energy resources came onto the grid.
CARB split electricity sector emissions into two broad categories: emissions from in-state power generation (including the portion of cogeneration emissions attributed to electricity generation) and emissions from imported electricity. In-state power generation produced about 40 million tons of CO2-equivalent emissions, while imported electricity produced about 22 million tons of carbon dioxide equivalent emissions. Emissions overall from the sector make up 15 percent of the total 2017 statewide greenhouse gas emissions.
Between 2011 and 2017, in-state rooftop solar-photovoltaic generation increased sixfold, while total solar generation increased 13 times during that period, according to CARB's report. In-state wind energy generation ramped up through 2013, but its trend has remained relatively constant since 2013, the report said.
A separate CARB report that was also published last week found that transport refrigeration units, which are trucks that transport food and other perishable goods, are emitting more GHGs than previously estimated.
The previous emissions model assumed 76 percent of TRUs used a refrigerant called HFC-134a, which is a hydrofluorocarbon gas used for refrigeration and automobile air conditioners. The updated model assumes only 10 percent of TRUs use HFC-134a, while 90 percent use a refrigerant called R-404A, which has a higher global-warming potential.
According to the report, the previous refrigerant usage assumptions for TRUs may have been applicable to Europe, but did not reflect California's TRU refrigerant usage.
Emissions from high global-warming potential gases have continued to increase in California because they have been replacing ozone-depleting substances that were banned under the 1987 Montreal Protocol. In 2017, high-GWP gases comprised 4.7 percent of California's emissions, the majority of which are hydrofluorocarbons such as HFC-134a and R-404A.