Are California's wildfires threatening carbon neutrality?

Andrew Plantinga
smoke coming out of burnt forest

In 2018, former governor Governor Jerry Brown issued an Executive Order committing the State of California to carbon neutrality by 2045. Although greenhouse gas (GHG) emissions from fossil fuels and other sources have fallen since the mid-2000s, getting all the way to  zero net emissions will require much larger reductions. This could be achieved by combining more ambitious emissions cuts with offsets: activities like tree planting that pull CO2 out of the atmosphere. A 2018 report from emLab, The Nature Conservancy, and Bowdoin College found that natural climate solutions, including land conservation, restoration, and management, while not enough on their own, can put a sizable dent in California’s carbon budget.

But what a difference a year can make. In late August of 2020, California was battling almost 400 wildfires sparked by intense thunderstorms and aided by powerful winds and scorching heat. By the end of the year, over 4.2 million acres would burn, doubling the previous record set in 2018. Before 2020, about 14 million metric tons (MMT) of CO2 was released during a typical fire season in California, equivalent to 3% of the state’s annual GHG emissions. In 2020, that figure jumped to 112 MMT, or 25% of current emissions. If the 2020 wildfires are indeed the new normal, then the road to carbon neutrality in California is going to be a lot steeper.

As the fires raged in August, Governor Newsom announced a potential solution. In partnership with the federal government, the state would treat one million acres of land each year to remove hazardous fuels, making it easier for fire-fighters to control fires before they get big. Could fuels treatments also help California reach carbon neutrality?

In a new emLab report, Project Researcher Kyle Monper and I estimate the costs of reducing CO2 emissions from wildfires. Given the many strategies available to reduce or offset GHG emissions, we wanted to know if fuels treatments provide a low-cost way to achieve net zero emissions.

Our analysis utilizes the Biosum model developed by the U.S. Forest Service, which enabled us to simulate the effects of fuels treatments on the growth of forest stands over time, drawing on data for 2,300 plots scattered throughout California. The model provides estimates of carbon stored in forest vegetation, soils, and biomass removed by timber harvests and fuels treatments. We examined forest thinning projects that remove different amounts of biomass and used Biosum’s integrated cost model, OpCost, to estimate the cost of these interventions. 

cost curves for California

We also simulated how fires would impact each forest plot under the different thinning regimes, a process we repeated for three estimates of annual acres burned across the state: the historical average (500,000 acres), a below average area (100,000 acres) and an above average area (1,000,000 acres). The simulated fire emissions, together with the modeled stand and harvested carbon estimates, allowed us to calculate the cost of the different thinning projects, as well as their effect on carbon uptake or emissions for each plot. We compared these results to a business-as-usual baseline without forest thinning.

Our results are summarized by marginal cost curves in Figure 1.  

The curves measure the amount of carbon that can be sequestered per year, measured in thousands of tons on the horizontal axis, at costs below a given carbon price, measured in $/ton on the vertical axis. The three panels correspond to the statewide annual estimates of acres burned and each panel shows marginal costs with (green) and without (red) avoided wildfire emissions.

Our main finding is that fuels treatments are an extremely expensive way to offset CO2 emissions. Since 2018, auction prices in California’s carbon market have been about $16/ton. At these prices, it would only be cost effective to sequester a negligible amount of carbon with thinning projects. Even if prices rose to $100/ton, it would only be economically worthwhile to sequester 200,000 tons of carbon annually in the above average burn scenario. This is only 0.2% of the emissions from the 2020 fires. There are other good reasons to manage fuels in California’s forests, including reducing losses of life and property from catastrophic wildfire, but our results indicate that thinning projects are not a cost-effective way to get to carbon neutrality. Our 2018 study found changes to timber harvest practices to be a much more promising approach.

headshot of Andrew Plantinga

Andrew Plantinga is the Director of emLab’s Land & Freshwater program and a professor at the Bren School for Environmental Science & Management at UC Santa Barbara.

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