In a first-of-its kind study examining the impact black carbon has on climate in California, researchers found the state’s efforts to reduce air pollution, particularly from diesel engines, has cut black carbon concentrations by 90% since 1966, without any noticeable disruption to the lives of the citizens of California, but with tremendous benefits to their health, as well as to climate protection. Concentrations have decreased by 50% since the late 1980’s, which is equivalent to reducing 21 million metric tons of carbon dioxide annually or the same as taking 4.1 million cars off California’s streets every year.
The 3-year study, funded by the California Air Resources Board and led by Scripps Distinguished Professor of Climate and Atmospheric Sciences Veerabhadran Ramanathan, was conducted by the University of California San Diego, Lawrence Berkeley National Laboratory at UC Berkeley, and the U.S. Department of Energy’s Pacific Northwest National Laboratory, and is the first-of-its-kind comprehensive regional assessment of the climate impact of black carbon on the Golden State.
Researchers used California’s extensive network of air pollution monitors as well as aircraft, satellites and computer models to study black carbon — tiny black particles released into the atmosphere from burning fossil fuels, wood, and waste. Black carbon is now recognized as the second leading cause of global warming, behind only carbon dioxide. It also is a major public health threat, killing an estimated six million people ever year around the world, and making countless more millions sick with respiratory and cardio-vascular illnesses.
California’s controls on emissions from diesel engines beginning in the 1970’s is in large part responsible for the dramatic reduction of black carbon in the state, although controls on other sources in the transport sector as well as industrial sources, and decreased burning of wood and waste, are also likely contributors. While the controls were put in place to improve public health, a co-benefit of reducing emissions of this major component of soot, according to the study, has been to slow the pace of climate change.
“We know that California’s programs to reduce emissions from diesel engines have helped clean up the air and protect public health,” said CARB chairman Mary D. Nichols. “This report makes it clear that our efforts to clean up the trucks and buses on our roads and highways also help us in the fight against climate change.”
Significantly, the study found that co-emitted pollutants such as sulfates and organic carbon did not decrease at the same time as the black carbon. Many of these co-emitted pollutants reflect light back into the atmosphere causing cooling that can offset some of the warming caused by black carbon. These results support a growing body of evidence that mitigation of black carbon emissions, particularly from diesel engines, can provide fast mitigation of global warming.
The study also found that brown carbon — a type of organic carbon that is typically ignored in climate models — is also a potent warming agent, offsetting up to 60 to 90% of the cooling caused by other lighter organic carbons. Brown carbon is emitted primarily from sources such as forest fires and residential wood burning, which previous studies believed to have negligible climate effect, or even a cooling effect. The results from the California study indicate that reducing emissions from these sources may also provide a benefit to climate mitigation.
“If California’s efforts in reducing black carbon can be replicated globally, we can slow down global warming in the coming decades by about 15 percent, in addition to protecting people’s lives,” Ramanathan said. “It is a win-win solution, if we also mitigate CO2 emissions simultaneously.”
“Reducing black carbon globally, along with other short-lived climate pollutants, including methane, tropospheric ozone, and hydrofluorocarbons, or HFCs, can cut the rate of global warming in half and the rate of warming in the Arctic by two-thirds over the next few decades,” said Durwood Zaelke, President of the Institute for Governance & Sustainable Development. “It also can save millions of lives every year, and significantly reduce crop damage.”
Efforts are already underway to phase down HFCs under the Montreal Protocol, a treaty that has already phased out nearly 100 similar chemicals by nearly 100%. U.S. President Obama and Chinese President Xi reached an agreement last week to work together to reduce HFCs using the Montreal Protocol.
“Success like this in California and with HFCs builds the momentum and confidence we need to address all sources of climate pollution, including carbon dioxide from energy production,” Zaelke added. “Enlisting national air pollution laws and institutions, and institutions like the Montreal Protocol is the fastest and most secure way to get climate protection.”
