Climate change from black carbon depends on altitude

Apr 14, 2011

Scientists have known for decades that black carbon aerosols add to global warming. These airborne particles made of sooty carbon are believed to be among the largest man-made contributors to global warming because they absorb solar radiation and heat the atmosphere. New research from Carnegie's Long Cao and Ken Caldeira, along with colleagues George Ban-Weiss and Govindasamy Bala, quantifies how black carbon's impact on climate depends on its altitude in the atmosphere. Their work, published online by the journal Climate Dynamics, could have important implications for combating global climate change.

Black carbon is emitted from and burning wood, among other sources. In the , it acts as an absorbing aerosol—a particle that absorbs the sun's heating rays. (Other types of reflect the sunlight back out into space, providing a cooling effect.) The climate effect of is difficult to quantify because these particles heat the air around them, affecting clouds even before they begin to heat the land and ocean surface.

The team's research involved idealized simulations of adding a theoretical megatonne of black carbon uniformly around the globe at different altitudes in the atmosphere. They found that the addition of black carbon near the land and ocean surface caused the surface to heat. As the of black carbon increased, surface warming decreased. The addition of black carbon to the stratosphere caused the land and oceans to cool. This cooling occurred despite the fact that the black carbon caused the Earth as a whole to absorb more energy from the sun. When black carbon is high in the atmosphere, it can lose its energy to space while helping to shade the land and ocean surface.

"Black carbon lower in the atmosphere is more effective at warming the surface, even though black carbon particles at higher altitudes absorb more ," said Ban-Weiss, formerly of Carnegie and currently at Lawrence Berkeley National Laboratory. He continued: "Just analyzing instantaneous changes in absorption of radiation from black carbon cannot accurately predict changes in surface temperatures. If we want a consistent framework for predicting changes in surface air temperature from black carbon we need to account for rapid atmospheric responses in things like clouds."

Black carbon also had varying effects on precipitation. In the lower layers it increased precipitation and in the upper layers it decreased precipitation, a result of changes in atmospheric stability.

"We showed that black carbon near Earth's surface has the greatest effect on global warming. Unfortunately, this is exactly where we are putting most of the black carbon that we add to the atmosphere," Caldeira said. "This black carbon also often causes health problems, so cleaning up these emissions would help both the environment and human health."

Major sources of black carbon emissions into the lower atmosphere include forest fires, cooking stoves, and emissions from trucks and automobiles. Aircraft are a notable source of emissions to the upper atmosphere.

"This study points out the importance of understanding the complexities of how human activities affect the globe. If we want humans to live well while protecting the environment, we need to understand how our activities affect climate," Caldeira said.

Explore further: Radioisotope studies show the continental crust formed 3 billion years ago

Related Stories

Cutting carbon dioxide helps prevent drying

Mar 24, 2011

Recent climate modeling has shown that reducing the concentration of carbon dioxide in the atmosphere would give the Earth a wetter climate in the short term. New research from Carnegie Global Ecology scientists Long Cao ...

Study finds black carbon implicated in global warming

Jul 29, 2010

Increasing the ratio of black carbon to sulfate in the atmosphere increases climate warming, suggests a study conducted by a University of Iowa professor and his colleagues and published in the July 25 issue of the journal ...

NASA probes the sources of the world's tiny pollutants

Jan 30, 2007

Pinpointing pollutant sources is an important part of the ongoing battle to improve air quality and to understand its impact on climate. Scientists using NASA data recently tracked the path and distribution ...

The mystery of particles

Jun 19, 2009

Particles cool down the climate, but to which extent? This has remained an unanswered question for scientists. A new article in Science by Gunnar Myhre at CICERO, Norway, brings the scientific community a step closer to sol ...

Recommended for you

ESA image: Northwest Sardinia

18 hours ago

This image over part of the Italian island of Sardinia comes from the very first acquisition by the Sentinel-2A satellite.

Experiments open window on landscape formation

Jul 02, 2015

University of Oregon geologists have seen ridges and valleys form in real time and—even though the work was a fast-forwarded operation done in a laboratory setting—they now have an idea of how climate ...

NASA image: Canadian wildfires continue

Jul 02, 2015

Canada is reeling from an early fire season this year as dozens of fires ravage at least three provinces of the country. All of the following reports are as of July 2, 2015.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.