Global Warming Compliance Offsets & Air Quality in California

The document examines the impact of emissions offsets on air quality in California under the Global Warming Solutions Act (AB 32). It highlights a University of California at Berkeley study showing that while in-state offsets produce mixed results—reducing methane but increasing nitrogen oxides (NOx)—out-of-state offsets lead to an increase in nearly every air pollutant, effectively exporting air quality co-benefits away from the state.

• California's Global Warming Solutions Act (AB 32) aims to reduce global warming pollution to 1990 levels by 2020, using a combination of sectoral regulations for 80 percent of reductions and a cap-and-trade program for the remaining 20 percent. The California Air Resources Board (CARB) proposed that offsets could replace up to 49 percent of the total reductions relative to 2012 emissions.
• Using offsets based exclusively within California (primarily in forestry, landfill, and agriculture) results in mixed air quality outcomes compared to implementing AB 32 without offsets. While emissions of methane and toxic gases like benzene decrease, smog-forming nitrogen oxide (NOx) levels increase because the entities buying offsets typically have more NOx-intensive operations than the sellers.
• The use of out-of-state offsets to achieve half or more of the cap-and-trade reductions leads to an increase in nearly every air pollutant relative to a no-offset scenario. If all cap-and-trade reductions are met via out-of-state offsets, 2020 levels of NOx and particulate matter (PM) could increase by approximately 4,000 and 2,000 tons per year, respectively. Specifically, PM2.5 would increase by nearly 400 tons per year, which is equivalent to the annual emissions of about 9,000 big-rig trucks.

APA

Union of Concerned Scientists (2009). Global Warming Compliance Offsets & Air Quality in California. https://www.ucs.org/sites/default/files/attach/2018/02/offsets-and-co-pollutants-fact-sheet%255B1%255D.pdf

Chicago

Union of Concerned Scientists. Global Warming Compliance Offsets & Air Quality in California. 2009. https://www.ucs.org/sites/default/files/attach/2018/02/offsets-and-co-pollutants-fact-sheet%255B1%255D.pdf.

Wikipedia

{{cite report |author=Union of Concerned Scientists |title=Global Warming Compliance Offsets & Air Quality in California |date=March 2009 |url=https://www.ucs.org/sites/default/files/attach/2018/02/offsets-and-co-pollutants-fact-sheet%255B1%255D.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{unionofconcernedscientists2009global, author = {{Union of Concerned Scientists}}, title = {{Global Warming Compliance Offsets \& Air Quality in California}}, institution = {Union of Concerned Scientists}, year = {2009}, month = mar, url = {https://www.ucs.org/sites/default/files/attach/2018/02/offsets-and-co-pollutants-fact-sheet%255B1%255D.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }