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California 2017 GHG inventory shows 1.2% total drop from 2016; transportation sector emissions up 1%

The California Air Resources Board’s latest state inventory of greenhouse gas emissions shows that California’s GHG emissions continue to decrease. In 2017, emissions from GHG emitting activities statewide were 424 million metric tons of CO2 equivalent (MMTCO2e), 5 MMTCO2e lower than 2016 levels and 7 MMTCO2e below the 2020 GHG Limit of 431 MMTCO2e.

These reductions have occurred while California’s economy has continued to grow. Compared to 2016, California’s GDP grew 3.6% while the carbon intensity of its economy declined by 4.5%.


Trends in California GHG Emissions. Changes in emissions by Scoping Plan sector between 2000 and 2017. Emissions are organized by the categories in the AB 32 Scoping Plan. Source: ARB.

The transportation sector remains the largest source of GHG emissions in the state, and saw a 1% increase in emissions in 2017. This is, however, the lowest growth rate over the past 4 years. Transportation sector emission sources include combustion of fuels utilized in-state that are used by on-road and off-road vehicles, aviation, rail, and water-borne vehicles, as well as a few other smaller sources.


2017 GHG Emissions by Scoping Plan Sector and Sub-Sector Category. The inner ring shows the broad Scoping Plan sectors. The outer ring breaks out the broad sectors into sub-sectors or emission categories under each sector.

The transportation sector represents tailpipe emissions from on-road vehicles and direct emissions from other off-road mobile sources. It does not include emissions from petroleum refineries and oil production. Source: ARB

Emissions from transportation sources were relatively constant from 2002 through 2007, declined through 2013, then increased by 9.0 MMTCO2e (6%) from 2013 to 2017. Emissions from gasoline used in on-road vehicles are the main driver of that increase.

Regulations, improved fuel efficiency of the state’s vehicle fleet, and higher market penetration of zero-emission vehicles drive down emissions over time; but population growth, lower fuel prices, more consumer and economic activity, and higher overall employment are factors that increase fuel use.


Overview of GHG Emissions from the Transportation Sector. “Transportation Total” is the sum of “On- Road Total,” “Aviation + Rail + Ships,” and “Off-Road + Unspecified.” “On-Road Total” is the sum of “Passenger Vehicles” and “Heavy Duty Vehicles.” The size of the symbols denotes the summing; larger symbols indicate what is summed to “Transportation Total” and small circles indicate what is summed to “On-Road Total.”

Biofuels such as ethanol, biodiesel, and renewable diesel can displace fossil fuels and reduce the amount of fossil-based CO2 emissions released into the atmosphere. The percent of biodiesel and renewable diesel in the total diesel blend have shown a significant growth in recent years, going from 1% in 2012 to 18% in 2017.

Other notable highlights in the inventory include:

  • For the first time since California started to track GHG emissions, in-state and total electricity generation from zero-GHG sources (for purposes of the GHG inventory, these include solar, hydro, wind, and nuclear) exceeded generation from GHG-emitting sources.


    In-State Hydro, Solar, and Wind Electricity Generation. Electricity generated by California’s in-state wind power projects, large commercial-scale solar power projects, rooftop solar panels, and hydropower generation stations. The unit is in terawatt-hour (1 TWh = 109 kWh).

  • Emissions from all other sectors have remained relatively constant in recent years, although emissions from high Global Warming Potential (GWP) gases have continued to increase as they replace Ozone Depleting Substances (ODS) banned under the 1987 Montreal Protocol.


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