Tag Archives: atmosphere

Black Carbon's Day on the Hill

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Drew Shindell (left), Veerabhadran Ramanathan, and Tami Bond speak with Representative Edward Markey after the three scientists testified. Credit: NASA/Voiland

Leading aerosol scientists, including NASA’s Drew Shindell, explained the intricacies of a sooty component of smoke called black carbon to members of the Select Committee on Energy Independence and Global Warming during a hearing on Capitol Hill last month.

Their message: controlling black carbon emissions could be a win-win for both human health and the environment.

Not only can partially combusted particles of carbon lodge in the human respiratory system and cause disease, the panelists explained, they also contribute to climate change by warming the atmosphere and changing the way Earth reflects sunlight back into space.

Three lawmakers—Representative Edward Markey (D-Mass.), Representative Jay Inslee (D-Wash.), and Representative Emanuel Cleaver (D-Mo.)—questioned the scientists.

Tami Bond, a black carbon specialist from the University of Illinois, began the hearing by offering a summary of black carbon’s potent short-term climate impacts. She noted, for example, that:

•     One ounce of black carbon absorbs as much sunlight as would fall on an entire tennis court.

•     A pound of black carbon absorbs 650 times as much energy during its one-to-two week lifetime as one pound of carbon dioxide gas would absorb during 100 years.

•     An old diesel truck driving 20 miles would emit about one-third of an ounce of black carbon and 70 pounds of carbon dioxide. The carbon dioxide from that truck would have five times the warming power of the black carbon, but it would spread out over 100 years. The truck’s more potent black carbon impact would have an effect in the span of a few weeks.

Drew Shindell, a climate modeler from NASA’s Goddard Institute for Space Studies (GISS) in New York City, provided more details about where black carbon comes from and how much impact it has on Earth’s climate.

As seen in this scanning electron microscope still image, small chain-like aggregates of soot cling to larger sulfate aerosol particles.  Credit: Arizona State University/Peter Buseck

Diesel vehicles, agricultural burning and wildfires, and residential cooking stoves are key sources of black carbon. However, combustion that occurs at higher temperatures — such as the type that takes place in power plants — does not produce much of the substance.

Shindell said climate models from NASA GISS and elsewhere show that 15 to 55 percent of global warming is due to black carbon. The wide range is primarily because of incomplete knowledge about how black carbon and clouds interact.

One of the more interesting questions came from Rep. Inslee, who asked the scientists whether black carbon’s impact is due to the fact that it absorbs sunlight and warms the atmosphere, or because it covers snow and ice with dark soot, which reduces Earth’s albedo and makes the planet less reflective.

Veerabhadran Ramanathan , a professor at the Scripps Institution of Oceanography, responded: “The albedo effect contributes about 10 percent of the total black carbon effect. But if you look in the Arctic or in the alpine glaciers, then the darkening effect may be the dominant effect.”

Shindell added that the scientific understanding of black carbon’s impact varies by region. “In places like the Himalayas, the results are somewhat ambiguous,” said Shindell. Over Himalayan glaciers, large amounts of dust — which also absorb radiation — and other pollutants in the air may dampen the effect. “In the Arctic, which tends to be very far from dust sources, the snow is very clean, so the effect is extremely large.” Increasing levels of black carbon combined with decreasing levels of sulfates may account for more than half of the accelerated warming in the last few decades, Shindell’s research suggests. 

Inslee also expressed frustration about the lack of understanding of science and climate change among his fellow lawmakers.”If I was scientist and I knew what was going on out there, I’d be in somebody’s grill, telling them we need action,” he said. “And yet you just don’t see that from the scientific community….Why doesn’t that happen? Should it happen?”

 Drew Shindell testifies as Veerabhadran Ramanathan looks on.
Credit: Committee on Energy Independence and Global Warming

The scientific method and the culture of scientists, Bond replied, makes it very difficult for scientists to lobby lawmakers or advocate a policy position and remain credible. “This is a difficult question and has to do with the nature of scientists and how they approach science,” she said. “If you have an action outcome, one is almost afraid that you’ll affect the science because you’re supposed to look at it dispassionately. How we conduct our business, 99.9 percent of the time, we must step back from what we want the outcome to be. We’re not allowed to want an outcome.”

Adam Voiland, NASA’s Earth Science News Team

Smog Blog Outtakes

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On Earth Day, we published an interview about the “smog blog” created by Ray Hoff of the University of Maryland – Baltimore County. Today, we follow up by sharing this video, which has some striking shots of laser pulses from the instrument that Hoff’s atmospheric LIDAR group uses to take air quality measurements near Baltimore.


Plus, here are some outtakes from Hoff that did not fit into the original interview:

On the importance of satellites…
“We spend quite a bit of time trying to use satellite measurements as a surrogate for what we see on the ground because the Environmental Protection Agency can’t be everywhere. EPA has a thousand monitors in the United States, but those monitors are largely in urban areas, and they can be spaced quite far apart. There are, for example, no EPA samplers in Wyoming. NASA satellites can look everywhere.”

On why satellite measurements of aerosols are less accurate in the western U.S…
“In the West, the correlation between what happens on the ground is worse for two reasons. The land surface out in the western United States does not have as much vegetation, so it’s brighter and more difficult for NASA satellites to see the aerosols from space. The other thing is that there are a lot of fires in the West, which make it challenging to distinguish between aerosol types.”

On the challenges facing air quality researchers…
“One of the things they’d really like to have is better measurements of ozone at the ground level. Much of the ozone we have on the planet is in the stratosphere, about 20 kilometers or 15 miles up, and it’s hard to see through the ozone layer, since it’s so thick. We have to combine models with measurements from the ground and NASA airborne platforms, but the difficulty of seeing through this layer to surface ozone is kind of the holy grail of tropospheric air quality research right now.”

On geoengineering the climate with sulfate aerosols…
“A Nobel Prize winner has suggested putting more pollutants in the atmosphere in order to keep the planet cool. I actually think that’s a rather poor experiment for us to be trying with so little knowledge of how the atmosphere works. Humans have a pretty bad record of trying to “fix the planet.”

–Adam Voiland, NASA’s Earth Science News Team

Is Coagulation Geoengineering's Achilles' Heel?

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Jason English, a graduate student at the University of Colorado at Boulder and a participant in NASA’s Graduate School Researchers Program, chats with us about some of his recent research into geoengineering.

WoE: Do you find there is a taboo of sorts against studying geoengineering among Earth scientists? It’s fairly unusual to see the topic come up at conferences, so your poster caught our eye.

English: There is more acceptance of studying it in just the last couple of years. I think scientists are facing the reality that countries aren’t doing much to slow the emissions of greenhouse gases. Eventually, we may have to choose between the risks and consequences of climate change and the risks and consequences of climate engineering. The only way to make an educated decision about that is to study it.

WoE: What type of geoengineering are you focusing on?

English: For my PhD, I have been looking at stratospheric aerosols.

WoE: Hold up. What are stratospheric aerosols?

English: They’re the tiny particles that are aloft in the atmosphere about 20 kilometers above the surface of the Earth. One of the leading geoengineering ideas is to inject aerosols into the stratosphere. I decided, after getting help and input from colleagues such as Michael Mills and Brian Toon, to set up a computer model that would analyze exactly how something like that would work.

WoE: And what do stratospheric aerosols have to do with climate?

English: People have suggested we could use a type of a particle for geoengineering that is actually composed of tiny droplets of sulfuric acid. Those are called sulfates. Sulfates reflect sunlight. If you have a layer of these particles up in the stratosphere they reflect part of the incoming solar radiation from the sun back to space. Overall, they have a cooling effect.

WoE: And sulfates can make it all the way up to the stratosphere?

English: Yes, some of the stronger volcanic eruptions can send particles into the stratosphere. They take a couple of years to settle back down to the surface. Very tiny amounts from power plants and other sources can also make it up that far.

WoE: I get that you modeled what might happen if humans decided to inject sulfates into the stratosphere, but what was the precise question you set out to answer?

English: There have been a few other scientists who have looked at geoengineering using stratospheric aerosols, but they didn’t simulate all the processes that can affect the particles. Recently, a team led by Patricia Heckendorn, a researcher based in Zurich, simulated all of these processes in a 2D model and found that the effectiveness of sulfate geoengineering diminished as more sulfate was added. I wanted to use a 3D model that looked at all of the processes, and I wanted to compare our results to Heckendorn’s.

WoE: What processes did you include that others didn’t?

English: For example, our model simulates coagulation, the process by which multiple particles can combine to become one. We also included nucleation – that’s when tiny gas molecules condense on each other to form liquid droplets. Also condensational growth. If you watch, say, water drops grow bigger and bigger on a piece of grass on a foggy morning you’re looking at condensational growth.

WoE: What did you find when you included all of that in your model?

English: What we found was that effective geoengineering required injecting larger masses of sulfuric acid than some have hoped because the particles coagulate and get much bigger than thought. Larger particles fall out of the stratosphere faster to the surface, so they’re not as effective at reflecting light. This matched Heckendorn’s results.

WoE: How much less effective?

English: It depends on how much sulfate we add. The more we add the less effective they become.

WoE: That’s the opposite of what people probably think…

English: It still gets more effective as you add more, but it has a diminishing return. We haven’t done a detailed assessment yet, but the group led by Heckendorn did, and they had a similar result. They found that you would need to inject more than 10 million metric tons of sulfur into the stratosphere per year if you wanted to offset the current forcing from greenhouse gases. People used to think it could be done with about 3 million metric tons.

WoE: Ten million metric tons sure sounds like a lot.

English: It is. Mount Pinatubo released about 10 million metric tons, but that was a one-time shot. Basically, we would need one or two Mount Pinatubo’s every single year.

WoE: Where do we go from here?

English: These results were surprising. If geoengineering is going to work, I think we’re realizing that scientists will need to look at new and creative ways to add particles to the stratosphere in such a way that they don’t grow too big and fall out too quickly.

Image Information: Astronauts took this image of Mount Etna erupting in 2002. Credit: NASA/JSC/Gateway to Astronaut Photography. The lower image is courtesy of Jason English.

–Adam Voiland, NASA’s Earth Science News Team

A Tale of Two Kenyas: Contradictions in Air Quality Stirred Researcher’s Pursuit of Atmospheric Science

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Charles Kironji Gatebe’s early years read like a cliché. He grew up barefoot and poor in the small Kenyan village of Kenda at the foot of Mount Kenya, the son of coffee sharecroppers who raised their family on pennies a day. He walked nearly 10 miles each way to school for nearly a decade. He lacked adequate texts and other school supplies.

What he didn’t lack on those long daily walks was clean air. It was the contrast between the clear skies of his boyhood home and the smog and fumes of the nation’s capital, Nairobi, that stirred within Gatebe a strong passion for science. In 1979, Gatebe (right) was selected to represent his elementary school at a national convention to celebrate the United Nations Educational, Scientific and Cultural Organization’s (UNESCO) International Year of the Child. He later won a physics prize in high school in 1984 from the Kenya Secondary Schools Science Congress. He enjoyed independent research so much that his physics teacher would allow him to conduct his own experiments in the lab alone at night or on weekends.

Gatebe’s passion, matched with natural aptitude, eventually led Gatebe to degrees from Kenya’s University of Nairobi and the University of the Witwatersrand in South Africa. Now a climatologist with a joint appointment at NASA’s Goddard Space Flight Center and the University of Maryland-Baltimore County, Gatebe has fashioned an award-winning career – including the rare honor of the World Meteorological Organization’s Young Scientist Award in 2000, and awards from the Kenyan government, German Academic Exchange Services, SysTem for Analysis, Research and Training (START), and the International Program in the Physical Sciences — for his innovative research on air pollution and its sources and effects on his country.

“Air quality in Kenya’s villages was and continues to be significantly different from the smog encountered in Nairobi. They vary so much that it seems you’re virtually in two distinct countries,” said Gatebe when asked to share what sparked his study of Kenya’s air pollution. During his graduate studies at the University of Nairobi, he devised a few climate projects that unexpectedly got the attention of the Kenyan government and United Nations Environment Program. One of those was a modeling experiment to measure vehicle pollution and predict pollution levels from the average speed and number of cars in use.

Gatebe also investigated the origins of the city’s air pollution; that is, how much Nairobi’s citizens and industry generated compared to what was transported in from other countries. “Charles’ Kenyan air quality research was quite breathtaking and significant,” said Michael King, a senior atmospheric scientist at the University of Colorado and former senior project scientist at NASA Goddard who recruited Gatebe to NASA in 1999. “It involved him regularly hiking to the top of Mount Kenya – which sits roughly on the equator — and collecting air samples of atmospheric aerosol particles that he analyzed for their composition to distinguish dust and other particles from local sources from pollutants arriving from as far away as southern Africa, India and the Sahara.”

The acclaim from the study came as a surprise, Gatebe says, but motivated him to stay the course. He knew he’d found his niche.

As a former child scientist, Gatebe is eager to inspire more kids to get involved in science. He’s dedicated himself to NASA’s Global Learning and Observations to Benefit the Environment (GLOBE) education program, and blogs about the science of current events for GLOBE’s Web site.

Gatebe’s latest work is based on what he calls an accidental discovery, not uncommon in science. In summer of 2008, he was part of a NASA field mission called Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS). Arctic wind currents can carry a haze that affects local climate. Gatebe and colleagues flew aboard planes through smoke blown over the Pacific Ocean from land-based fires to evaluate the composition of the pollution that eventually forms Arctic haze. 

A ship passed beneath Gatebe’s plane, through his measurement field, triggering a mass of sea foam in its wake. When he later evaluated visible and near-infrared data from NASA’s Cloud Absorption Radiometer instrument that took the measurements from aboard the plane, he noticed a spike in brightness in the vicinity of the ship’s path. The bubbles in the wake increased light reflectance off the ocean.

The irony of the discovery was quite amazing to Gatebe. Ships were long thought to pollute the air and contribute to warmer climate through exhaust emissions. But they also appear to have a counterbalancing effect of cooling local ocean surfaces by as much as four percent. What he doesn’t know yet is just how much the cooling effect offsets the warming effect on the nearby environment. He hopes that others will further the work so the question doesn’t go unanswered.  

–Gretchen Cook-Anderson, NASA’s Earth Science News Team

Charles K. Gatebe (top, courtesy of C. Gatebe);  Zebras with hazy Nairobi in the distance (bottom, courtesy of Michael King).  

Soaring for Science

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NASA's Global Hawk autonomous plane

The newest bird in NASA’s flock — the unmanned Global Hawk — took off at 7 a.m. Pacific time today (April 2) from Dryden Flight Research Center at Edwards Air Force Base in California. The flight is the first airborne checkout of the plane since it was loaded with 11 science instruments for the Global Hawk Pacific (GloPac) mission.

Pilots are also streamlining processes to coordinate the workload while the nearly autonomous plane is flying at altitudes above 60,000 feet (almost twice as high as a commercial airliner). Operators and mission researchers are using the day to make sure all instruments are operating properly while in flight — particularly at the cold temperatures of high altitude — and communicating clearly with the plane and ground controllers. Mission participants expect to begin collecting data when actual GloPac science flights begin over the Pacific Ocean later this month.

GloPac is the Global Hawk’s first scientific mission. Instruments will sample the chemical composition of air in Earth’s two lowest atmospheric layers — the stratosphere and troposphere — and profile the dynamics and meteorology of both. They also will observe the distribution of clouds and aerosol particles. The instruments are operated by scientists and technicians from seven science institutions and are funded by NASA and the National Oceanic and Atmospheric Administration (NOAA).

Paul Newman, the co-mission scientist for GloPac, has been blogging about the mission on Earth Observatory’s “Notes from the Field” site. Here are a few excerpts to whet your appetite…

…There is an old Latin quote: “Maxima omnium virtutum est patientia.” Or “patience is the greatest virtue.” When it comes to mounting science instruments on an aircraft, you need to continually return to that quote…

…During the integration this week, we’ve had to cut holes into the aircraft. I told Chris Naftel, the Global Hawk project manager, that we had to cut some holes into the plane for the Meteorological Measurement System. Chris replied: “I don’t want to hear anything about the holes. It pains me!” In spite of Chris’ pain, the little holes are critical for measuring winds. You’re now asking, what? Little holes? For winds? It’s actually a very slick little measurement that relies on the work of Daniel Bernoulli, a Dutch mathematician who lived in the 1700s…

Read more here …

Science at the Intersection of Air Quality and Climate Change

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Smog over New York. Credit: NASA

The atmosphere is a stew of gases and particles. Some affect climate. Others degrade air quality and threaten human health. Some do both. Some do neither. Many of them interact with and affect one other.

Ozone, for example, causes respiratory problems near the surface, but also functions as a greenhouse gas. Black carbon aerosol particles do the same, and also contribute to heart disease.

Other pollutants — notably sulfates and nitrates—create health problems but simultaneously reflect incoming sunlight and cool the climate. Some, like nitrogen oxide, are precursors to ozone, but also affect the abundance of the light- scattering pollutants that cool the climate.

All of this adds up to a question that keeps some climatologists up at night: Is it possible to reduce emissions of toxic air pollutants in a way that will mitigate global warming, or at least not make it worse?

For example, reducing black carbon has the potential to improve health and reduce global temperatures by as much as a degree. On the other hand, reducing sulfates—which industries often emit along with black carbon—could negate any reduction in warming that pollution controls might produce. (These are just a few examples from the dozens of gases and particles that scientists have to factor in tabulating Earth’s energy budget.)

Almut Arneth, a researcher from Lund University in Sweden, and colleagues, including NASA climatologist Nadine Unger, considered the question recently in a “perspectives” piece in Science. You can read the full paper here (though you may need to brush up on your atmospheric chemistry to understand the details). Unger and her coauthors sum the complicated situation up this way:

“Given the toxicity of pollutants, the question is not whether ever stricter air pollution controls will be implemented, but when and where. The jury is out on whether air pollution control will accelerate or mitigate climate change. Still, the studies available to date mostly suggest that air pollution control will accelerate warming in the coming decades.”

If that’s correct, not only do we have a bigger climate problem on our hands than we may have thought, but some will surely misinterpret the finding by concluding that we ought to continue polluting—or even ramp up the emission of certain pollutants with geoengineering—to stave off climate change, a point that NASA climatologist Gavin Schmidt made recently on RealClimate.

–Adam Voiland, NASA’s Earth Science News Team

Smelling the Air in Kanpur

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Winter haze piles up against the Himalayas above the Indo-Gangetic Plain.      (Credit: Earth Observatory)

“When the plane was about 30 minutes from touchdown, we could start to smell the air,” said David Giles. “It was shocking.”

Giles — a young scientist at NASA’s Goddard Space Flight Center — was en route to Kanpur, a large Indian industrial city on the banks of the Ganges river. Dust and soot tend to hover over the region, which is sandwiched between the sharp edge of the Tibetan Plateau to the north and the highlands of the Deccan Plateau to the south.

There’s so much soot in the air that satellites can routinely see a cloud of haze blanketing the region.

The bowl-like Indo-Gangetic Plain is second only to some parts of China for having the heaviest load of air pollution in the world. In the spring, when dust blows in from the deserts to the West, aerosols from factories, buses and trucks, and fires are especially heavy. So much so, in fact, that NASA researchers suggested recently that dust and soot may be driving the retreat of Himalayan glaciers by altering the monsoon.

Giles was in Kanpur to man one of NASA’s AERONET stations in the region as part of the ongoing TIGERZ campaign. He spent 17 days in Kanpur hauling the instrument around and getting harassed by local police officers, the occasional herd of roaming sheep and dust storms. In between all that, he spent the bulk of his time collecting measurements to determine whether dust and soot can glom onto one another to create new types of hybrid aerosols.

They do, he found, a seemingly mundane point but one that’s of considerable interest to the scientists trying to sort out how these two types of aerosols affect the climate. He presented his results in detail this week to colleagues at the American Geophysical Union fall meeting in San Francisco.

I nabbed him after his talk in the afternoon, to have a beer and talk through his travels. I asked him what was the most memorable part of the trip to India. “Well, it was unbelievably hot,” he said with a laugh. “Temperatures routinely hit 105 degrees.”

And how was the air? “You’d get used to it after a while,” said Giles, “but, at first, in the taxi, we were holding our sleeves over our mouths just to avoid breathing the stuff.”

Giles and colleagues using sun photometers to measure aerosols from a rooftop in Kanpur.  (Credit: Giles)

–Adam Voiland, NASA’s Earth Science News Team

Greenhouse Molecules Laid Bare

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The Earth is a bit like the human body; its temperature is very finely balanced, and when it gets slightly out of whack, big things can happen. In the case of our home planet, gases in the atmosphere play a vital role in maintaining this delicate equilibrium, by balancing the absorption and emission of all the electromagnetic radiation (microwaves, infrared waves, ultraviolet light and visible light, for example) reaching the surface of the Earth.

As reported recently, the Earth is getting warmer. Scientists believe the main driver behind this warming trend is rising levels of man-made greenhouse gases. These gases, which we pump out into the air, act to trap heat radiation near the surface of the Earth that would otherwise be sent back out into space. Carbon dioxide (CO2) is the Paris Hilton of greenhouse gases, and gets a lot of face time because its concentration in the atmosphere has increased relatively rapidly since the Industrial Revolution. But methane, nitrous oxide, hydrofluorocarbons (HFCs), chlorofluorocarbons (CFCs) and perfluorocarbons (PFCs) are also important agents of global warming. Some of them are actually much more potent than CO2 and they stick around for hundreds to thousands of years longer. This has some scientists concerned that these B-listers could actually impact global temperatures significantly more than CO2.

greenhouse warming cartoon

In a new paper, Partha Bera and colleagues at NASA’s Ames Research Center and Purdue University put these gases under the microscope to find out exactly why they are such powerful heat trappers. They focus on CFCs, HFCs and PFCs — all chemicals containing fluorine or chlorine — that are used in medicine, fridges, and as solvents, among other things. By probing the molecular structure of these compounds, they have found that molecules containing several fluorine atoms are especially strong greenhouse gases, for two reasons. First, unlike many other atmospheric molecules, they can absorb radiation that makes it through our atmosphere from space. Second, they absorb the radiation (and trap the heat) very efficiently, because of the nature of the fluorine bonds inside them. (In technical terms, fluorine atoms create a larger separation of electric charge within the molecule, and this helps the molecular bonds absorb electromagnetic radiation more effectively.) HFCs and other fluorine-based gases have been called “the worst greenhouse gases you’ve never heard of.” Now we know why.

Until now, scientists had not looked in detail at the underlying physical or chemical causes that make some molecules better global warmers than others. Bera and colleagues say that their work should help improve our “understanding [of] the physical characteristics of greenhouse gases, and specifically what makes an efficient greenhouse gas on a molecular level.” They hope their findings will be used by industry to develop more environmentally-friendly materials.

Amber Jenkins, NASA’s Global Climate Change team 

How Do Global Soot Models Measure Up?

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A image from a simulation that shows the spread of black carbon aerosols in Asia. Areas where the air was thick with
the pollution particles are white, while lower concentrations are transparent purple. (Credit:
Earth Observatory)

As NASA atmospheric scientist Eric Wilcox recently told Time magazine, emerging evidence suggests that a short-lived type of air pollution called black carbon—known popularly as soot—can exacerbate global warming by absorbing incoming solar radiation.

Yet pinning down precisely how much the black carbon exacerbates warming is no easy task, research conducted by Goddard Institute for Space Studies climatologist Dorothy Koch suggests. The study, published in Atmospheric Chemistry and Physics tracked how the predictions from 17 global black carbon models compared with actual measurements collected by airplane, satellite, and ground-based sensors. It shows, among other things, that models generally underestimate black carbon’s warming effect on climate.

Koch tested all the models in three ways. In the simplest of the three, she compared the models’ predictions to the amount of black carbon measured at the surface, finding that they matched real life reasonably well.

Her second test compared the models’ predictions to black carbon measurements made higher in the atmosphere using airplanes, and the results were much less clear cut. Though the models usually had too much black carbon over pollution sources, most had too little over remote regions such as the Arctic.

Koch’s final and most important test looked at how much solar radiation black carbon actually absorbs, an indicator of the amount of warming the particles actually produce. Again, the results were mixed. The models were largely accurate over North America and Europe, but were not for areas that have high levels of black carbon such as Central Africa, Southeast Asia, and the Amazon.

In a write-up on the Goddard Institute for Space Studies web site, Koch summarizes her findings this way:

We concluded from this study that most models have enough black carbon at ground level in polluted regions, too much in the atmosphere above source regions, but not enough in the Arctic where black carbon may play an important role in contributing to Arctic warming and ice/snow melt. The models’ soot generally does not absorb enough sunlight and therefore these models would underestimate black carbon heating effects. This probably results from underestimating the absorbing properties of the particles rather than the amount (mass) of black carbon.

Wondering how climate modelers can continue to close the gap between model predictions and reality? Koch put forward some advice on how to fine-tune the next generation of aerosols models. Her top three:

1) Account for mixing between black carbon and other components of the atmosphere,
2) Incorporate better measurements of particle size and source amount in some regions.
3) Continue to mine ongoing satellite and field campaigns for data about black carbon.

You can read more GISS science briefs and NASA news stories about black carbon here, here, and here.

–Adam Voiland, NASA’s Earth Science News Team

Fewer Southeastern Tornadoes Occur Following Dry Falls and Winters

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Rainfall irregularities as observed by NASA’s Tropical Rainfall
Measurement Mission  satellite. Credit: NASA

Perhaps Dorothy, from the famed film Wizard of Oz, should have hoped for a fall or wintertime drought. According to findings from a NASA-funded study published last June in Environmental Research Letters , dry fall and winter seasons in the southeastern United States mean it is less likely that Southern twisters will develop in springtime to sweep anyone off their feet.

Using rainfall data from NASA satellites, rain gauge information, and NOAA’s Storm Prediction Center tornado record dating back to 1952, University of Georgia meteorologists Marshall Shepherd and Tom Mote and Purdue University climatologist Dev Niyogi discovered a statistical tendency for drought-ravaged fall and winter seasons to pave the way for “below normal tornado days” in spring seasons that follow.


“This is conceptually similar to what Bill Gray’s been doing for more than 25 years when he predicts how active the hurricane season will be based on African rain,” said Shepherd, the study’s lead author, of the Colorado State University’s pioneer hurricane season forecaster.

They culled data from Northern Georgia and other parts of the southeast, but Shepherd and his colleagues believe their findings may have relevance for other regions. The new study also adds to the body of related work Shepherd and Niyogi are ushering, including their study earlier this year in the aftermath of Atlanta’s spring 2008 twister that linked urbanization and drought to tornado activity.

For Shepherd in particular, there’s no place like home when considering the geographical focus of much of his meteorological research. “Science is my proverbial yellow brick road,” explained Shepherd. “It’s taken me down some fascinating paths, especially in learning more in recent years about tornado phenomena in my own backyard.”


–Gretchen Cook Anderson, NASA’s Earth Science News Team

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