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Monday, December 6, 2021

Carbon dioxide has larger impact on the climate compared to black carbon, according to study

UC Davis researchers quantified the regional climate impacts of low-carbon energy adoption in California, and compared potential plans for future climate policies

A recently-published study from a group of UC Davis researchers analyzes the climate and environmental impact of low-carbon energy adoption in California. They found that the adoption of such a system doesn’t just lower long-lived greenhouse gasses such as carbon dioxide (CO2), but also short-lived pollutants and soot contained in particulate matter (PM).

California currently has a stated goal of reducing greenhouse gas emissions by 80% relative to 1990 levels. This greenhouse gas reduction scenario (GHG-Step) is intended to target long-lived climate pollutants (LLCP) such as CO2, but the fuels and technologies used for this adaptation also reduce levels of short-lived climate pollutants (SLCP).

This paper quantifies the potential change in regional climate forcing—the process of affecting climate through various forcing factors—in California under two potential futures: a Business-as-Usual (BAU) scenario and a GHG-Step scenario. The former is based on current climate rules and regulations such as those outlined under Assembly Bill 32, and the latter is based on a plan for getting emission levels to 80% below what they were in 1990.

Michael Kleeman, a co-author of the paper, describes why it is important to look at the different climate impacts of the BAU scenario and the GHG-Step scenario.

“In previous studies, we predicted major health benefits in the GHG reduction scenario due to reduced air pollution,” Kleeman said via email. “Most of that benefit was driven by reductions in airborne particulate matter concentrations. That same particulate matter contains light-absorbing compounds that act as warming agents for climate change. So we were curious to see if the particulate matter reductions also had significant climate benefits.”

Under the GHG-Step scenario, ground level PM2.5 decreased by 8.9%, which subsequently improved air quality, but this didn’t have much of an impact on the climate. The reduction of greenhouse gases, such as CO2, was associated with a much larger climate forcing in comparison to the reduction from PM2.5. Cort Anastasio, a professor in the department of land, air and water resources, talks about why this finding is not too surprising. 

“When you think about greenhouse gases, we know that carbon dioxide is the most important greenhouse gas [and] we know that it is very long-lived,” Anastasio said.

Kleeman addresses the need to study the climate differences between greenhouse gases and particulate matter, especially when considering how each of them can be controlled, and what kind of an impact they can have on the climate and the environment. 

“The particulate matter component of global warming can be controlled much more quickly than the CO2 component,” Kleeman said via email. “Policy makers seeking to address climate change may be counting on a fast response to future PM2.5 reductions to put off dealing with immediate reductions to CO2. It is important to quantify how much each pollutant contributes to climate change in California so that we know the local effects of our policies.”

According to Kleeman, this paper is the first to look at and quantify the effect of low-carbon energy systems described in California’s regional climate through PM2.5  radiative forcing, which will help to resolve details of emissions patterns and pollutants from the greenhouse gases and PM2.5 over California. 

“Hopefully the results of the paper will help inform decision makers that policies targeting GHG emissions are needed to [reduce] climate change in California,” Kleeman said via email. “Policies that seek to influence climate through changes to PM2.5 concentrations will be less effective even though they can be implemented more quickly.”

For Anikender Kumar, a postdoctoral researcher at UC Davis and lead author of the paper, this study is another step in shaping climate policy and setting priorities in California’s fight against climate change.

“The direct effect of carbon dioxide reduction is far greater than the effect of airborne particulate matter reduction in the greenhouse gas mitigation scenarios over California in this paper,” Kumar said via email. “I hope that policymakers will focus on reducing LLCPs as well as SLCPs for the better future with respect to health as well as climate.”

According to Anastasio, California makes a fairly low contribution to the global CO2 amount, but that doesn’t mean its efforts in lowering greenhouse gases aren’t significant. 

“California making a significant cut globally doesn’t make a big difference in the CO2 budget, but it does provide an example for the world,” Anastasio said.Written by: Simran Kalkat — science@theaggie.org

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