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Study finds that California clean diesel programs have slashed black carbon, a powerful short-term contributor to global warming

California’s air quality programs have forced a reduction in black carbon despite a significant increase in diesel fuel consumption. Click to enlarge.

In California, reductions in emissions of black carbon since the late 1980s—mostly from diesel engines as a result of air quality programs—have resulted in a measurable reduction of concentrations of global warming pollutants in the atmosphere, according to a study examining the impact of black carbon on California’s climate.

The study’s results support a growing body of scientific evidence that suggests it is possible relatively quickly to slow the pace of climate change regionally by reducing emissions of short-lived climate pollutants, like black carbon.

The study, funded by the California Air Resources Board (ARB) and led by Dr. Veerabhadran Ramanathan of the Scripps Institution of Oceanography at the University of California, San Diego, estimates that reductions in black carbon as a result of clean air regulations were equivalent to reducing carbon dioxide emissions in California by 21 million metric tons annually or taking more than 4 million cars off California roads every year. The reductions occurred during a time when diesel fuel consumption increased by about a factor of five.

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. It is a win-win solution if we also mitigate carbon dioxide emissions simultaneously.

—Dr. V. Ramanathan

Black carbon—tiny soot particles released into the atmosphere by burning fuels—has been linked to adverse health and environmental impacts through decades of scientific research. It is also one of the major short-lived contributors to climate change. The major sources of black carbon in California are diesel-burning mobile sources, residential wood burning in fireplaces and heaters, agricultural burning and wildfires.

Black carbon has the effect of warming the atmosphere because it is effective at absorbing sunlight. However, it is emitted together with a range of other particle pollutants, including organic carbon, sulfur and other chemicals, some of which have a cooling effect, typically by reflecting sunlight. Reducing diesel emissions can therefore lead to a reduction of both warming and cooling particles.

The report, however, is the first to confirm, based on both observations and computer modeling, that the warming effect of black carbon dominates, overwhelming any cooling effect of other pollutants. This confirms the positive impact reducing diesel emissions has on fighting climate change.

...for regions like California, where mitigation policies have historically targeted primarily fossil fuel sources leading to a large decrease in atmospheric BC, the climate benefits of direct forcing reduction has masked the net warming due to greenhouse gases by a measurable fraction (estimated to be 5% of the CO2 warming potential). This climate benefit dates back to at least the 1960s, and is currently ongoing. Brown carbon, emitted from residential wood burning is found to be another attractive target for policy makers seeking to combat anthropogenic climate change.

—“Black Carbon and Regional Climate of California”

The 3-year-study, titled “Black Carbon and Regional Climate of California,” was conducted by UC San Diego and the US Department of Energy’s Lawrence Berkeley National Laboratory (LBNL) and Pacific Northwest National Laboratory (PNNL). It is the first comprehensive regional assessment of the climate impact of black carbon on California. In conducting the study, scientists used computer models and air pollution data collected by aircraft, satellite and ground monitors.

According to co-author Dr. Tom Kirchstetter of LBNL, black carbon levels have decreased by about 90% over a 45-year period, beginning with the establishment of CARB in 1967, mostly as a result of state regulations for diesel engine emissions. Researchers found the state’s efforts to reduce diesel emissions to have lessened the impact of global warming on California, supporting earlier theoretical computer modeling by Dr. Mark Jacobson of Stanford University that reducing black carbon from diesel combustion is a potent climate cooler.

The study took a conservative approach in examining the impact black carbon has on the Golden State. Researchers considered emissions only from diesel-powered trucks and buses, and off-road diesel equipment and vehicles to estimate the equivalent reduction of carbon dioxide.

When all sources of black carbon emissions from diesel fuel combustion are considered, including farming and construction equipment, trains and ships, the reduction in carbon dioxide emissions can be as high as 50 million metric tons per year over the past 20 years. That’s roughly equal to a 13% reduction in the total annual carbon dioxide emissions in California.

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.

In addition, they study found that black carbon particles increased the number of drops of water in clouds, while decreasing the size of those drops, a condition that can reduce or delay rain.




This makes sense even tough naysayers will never believe it.


Propane with diesel reduces particulates.



Global Warming - what Global Warming? Al Gore should be whacked with a hockey stick.

Kit P

Al Gore was kicked in the head by a mule as a child which explains a lot. He missed school when they were explaining scientific method.

Bob Wallace

Reducing black carbon emissions may be a way to quickly and easily reduce the rate of climate change.

Carbon black, while in the air, intercepts sunlight and converts it to heat. Once is settles down on snow/ice it greatly reduces albedo. Now that the Greenland ice cover is starting to melt the accumulated carbon black/soot is starting to turn the surface very dim and greatly increase heating/melt.

One way to lower carbon black is to help people switch from kerosene to electricity.

Micro-solar systems that let people switch from kerosene to LED lighting is being very successful.

Bangladesh has a great program that has installed over 1 million systems. They hit that level sometime back and are installing more than 1,000 new systems per day.

For less than the cost of kerosene people are able to purchase a small solar system and pay for it over a number of months. When the system is paid off they can either use the money they used to spend on kerosene for something else or move to a larger system.

They get much better quality lighting, cleaner air to breathe, cell phone charging and the planet gets a lot less carbon black.

(I really doubt that the major climate models exclude carbon black. Climate scientists are pretty bright folks.)


Global Warming hysteria has about run its course, It can join Alar, Acid rain, DDT, CO2, plastic bags, aluminum cans, coal, CO2,and Black carbon, and other assorted challenges to mass hysteria in the Pantheon of Paranoia.

Good Riddance. Al Gore and James Hansen have had more then their allotted 15 minutes of "fame".

BW, You would be surprised just how stupid the established Warmists really are.

Nick Lyons

To all you deniers out there: climate change is happening. Show me a credible climate scientist that doesn't support the reality of AGW. If you lived in Alaska, as I did for seven of the past eight years, you would not be able to deny what's happening.


To D and friends: You are not smarter than these people; http://climate.nasa.gov/scientific-consensus


Isn't it wonderful. Only "credible" Warmists need be consulted.

BTW, I as a scientist know and understand the scientific method. I can distinguish between bald assertions, and valid proven scientific facts.

Global Warming via GHGs was a valid scientific, qualitative-only, hypothesis, when introduced. But several decades of quantitative research has now established that the true effect is tiny at best and, de minimus, of no concern any longer. At these levels it may probably be entirely beneficial.

I fail to see how the World ends by a fluctuation of a few tenths of degrees in centuries, or can alter much when a diurnial temperature cycle can be a order of magnitude larger, never mind an annual cycle that is even larger still.

I would certainly like the Warmist "pseudo-intelligentsia" to get their act together. They have said the reason Warming is not happening is that "Black Carbon" is preventing temperatures from rising. Yet here they argue that "Black Carbon is" a significant Warming agent.

It can't be both. Well which is it??


You're a scientist? Really? What's you're h-index?

Trevor Carlson

While it is patently obvious and easy to find out who has financed efforts to debunk global warming it is relatively difficult to understand who exactly determines which studies get funded.
Just by funding certain studies that indicate or assume global warming and not other studies that indicate or assume cooling one could skew the majority of scientific opinion. By asking ones-self the question of what power and influence could be gained by creating a global problem that can unite countries and peoples to combat helps illuminate the probable motivation behind the federal funding.

I'm not saying there is or isn't climate change - just consider there may be hidden agendas on both sides of the debate. Considering the power governments hold compared to individual corporations and citizens should there be a clash of agenda on a complex issue... trusting the government is portraying the whole truth and nothing but - is foolish.


I'm sorry Trevor but that's laughable. It is very easy to understand who exactly determines which studies get funded. It's who ever has the money. And there are enough different sources of funding out there to ensure that both sides of the debate get a share.

Or maybe your point is that "the government" and its control of "federal funding" is the problem? Well there's an even easier answer to that: Go find another government. Do you really think the Dick Cheney Whitehouse would have suppressed research that disproved climate change? Do you think the government of Stephen Harper would? Howabout the oil rich Saudi government?


The Harper Government is fighting back most environmental groups efforts by cutting funds for Climate Change research. Most Pro Oil Groups and Pro-Oil Governments do the same.

Pro-Oil Governments can always be changed (and it will be done in Canada and in many other countries) but Pro-Oil Groups financed by Oil $$$$ will be around to the last drop?

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