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In Tsakopoulos Investments v. County of Sacramento (2023) 95 Cal. App. 5th 280, the Third District Court of Appeal (“Court”) upheld the County of Sacramento’s (“County”) certification of the Mather South Community Master Plan (the “Master Plan” or “Project”) environmental impact report (EIR) under the California Environmental Quality Act (CEQA). In the published portion of the opinion, the Court held that the County’s choice of numeric significance thresholds for greenhouse gas (GHG) emissions in the Master Plan EIR was supported by substantial evidence, including the use of local and sector-specific data. To that end, the Court denied plaintiff Tsakopoulos Investments, LLC’s (“Tsakopoulos”) CEQA challenge to the County’s approval of the Project.


In 2020, the County approved a Master Plan and certified the EIR for an 848-acre project in Sacramento County, which included thousands of residential units, an environmental education campus, a research and development park, two elementary schools, commercial retail space, and open space. Tsakopoulos filed a petition for a writ of mandate asserting that the County’s approval of the Project violated CEQA; the trial court denied the petition.

On appeal, Tsakopoulos challenged the trial court’s judgment on two grounds: (1) the climate change analysis of the EIR was based on a methodology that the Supreme Court of California in Center for Biological Diversity v. Department of Fish &Wildlife (2015) 62 Cal.4th 204 (“Center for Biological Diversity”) and the Fourth District Court of Appeal in Golden Door Properties, LLC v. County of San Diego (2018) 27 Cal.App.5th 892 (“Golden Door”) had previously rejected, and (2) the County failed to assess the impacts of construction-related GHG emissions and analyze the human health impacts of the Project’s emissions.

Appeal Court Decision

Before reaching Tsakopoulos’ CEQA challenge, the Court provided a detailed overview of the legislative and regulatory background governing the GHG reductions in California, including the California Global Warming Solutions Act of 2006 (“AB 32”) and the California State Air Resources Board’s (“CARB”) 2008 Climate Change Scoping Plan (“2008 Scoping Plan”) prepared to implement the AB 32 goal of reducing GHG levels in the state to 1990 levels by the year 2020. In the 2008 Scoping Plan, CARB provided a target of a 29% statewide reduction in “business-as-usual” (“BAU”) GHG emissions, i.e., defined as the level of GHG emissions in 2020 if no reduction actions were taken.

The Court then turned to Tsakopoulos’ argument and distinguished the County’s GHG methodology in the Master Plan EIR from the methodologies previously rejected by the Supreme Court of California and the Fourth District Court of Appeal in the Center for Biological Diversity and Golden Door.

In Center for Biological Diversity, the EIR used CARB’s 29% statewide emissions reduction target below BAU as a significance threshold at a project level. The Supreme Court upheld the lead agency’s discretion to use the AB 32 target as a significance threshold under CEQA, but found no substantial evidence in the record to show that the statewide goal of a 29% reduction below BAU was “the same for an individual project as for the entire state population and economy.”

And in Golden Door, the Fourth District struck down a county-wide, uniform significance threshold of 4.9 metric tons of CO2 equivalent per person per year using statewide rather than local data, and used the same metric across all the land use sectors. The Fourth District found a lack of substantial evidence in the record to explain why it was sufficient to use a statewide efficiency metric, irrespective of the land use categories, as an appropriate threshold of significance for individual projects located exclusively within the County of San Diego.

The Court in Tsakopoulos held that the GHG threshold of significance in the Master Plan EIR was distinguishable from the significance thresholds invalidated in those two cases. Unlike Center for Biological Diversity, where the EIR simply used the statewide GHG emissions reduction target of 29% below BAU without explaining how it correlated at a project level, the County here developed County-specific GHG significance thresholds using Countywide data for different sectors, namely residential, commercial, industrial, and transportation sectors. The County then set a sector-by-sector reduction threshold for use at an individual project level. Similarly, unlike Golden Door, using countywide and sector-specific data rather than statewide data, the Master Plan EIR developed different per capita local thresholds of significance to apply to each sector at a project level. Thus, the Master Plan EIR’s GHG significance thresholds were not simply extrapolated from statewide data, without any evidence or explanation, but were supported with relevant and substantial evidence in the record.

Similarly, relying on the substantial evidence in the record, the Court held that the County had adequately analyzed the impacts of construction-related GHG emissions and the human health impacts associated with project emissions.


This case upholds the principle that the lead agencies are afforded substantial discretion in determining the thresholds of significance and the methodology used to assess a project’s impacts under CEQA, as long as the agency’s methodologies, significance thresholds, and assumptions are supported by substantial evidence in the record. In case of GHG significance threshold, this case upholds the use of the CARB’s emission reduction goals for a project level if the lead agencies incorporate sector and region-specific data when determining a project’s GHG impacts.