Volcanic eruptions slow down climate change - temporarily

Space Daily via SPX: Although global concentration of greenhouse gases in the atmosphere has continuously increased over the past decade, the mean global surface temperature has not followed the same path. A team of international reseachers, KIT scientists among them, have now found an explanation for this slowing down in global warming: the incoming solar radiation in the years 2008-2011 was twice as much reflected by volcanic aerosol particles in the lowest part of the stratosphere than previously thought. ....

For the lowest part of the stratosphere - i. e. the layer between 10 and 16 kilometres - little information was available so far, but now the international IAGOS-CARIBIC climate project combined with satellite observations from the CALIPSO lidar provided new essential information. According to the study, the cooling effect due to volcanic eruptions was clearly underestimated by climate models used for the last Intergovernmental Panel on Climate Change (IPCC) report.

Led by the University of Lund, Sweden, and supported by the NASA Langley Research Center, USA, and the Royal Netherlands Meteorological Institute, three major German atmospheric research institutes were also involved: the Max Planck Institute for Chemistry in Mainz (
MPI-C), the Leibniz Institute for Tropospheric Research in Leipzig (TROPOS) and the Karlsruhe Institute of Technology (KIT). Since more frequent volcanic eruptions and the subsequent cooling effect are only temporary the rise of Earths' temperature will speed up again. The reason is the still continuously increasing greenhouse gas concentration, the scientists say.

..."Overall our results emphasize that even smaller volcanic eruptions are more important for the Earth's climate than expected", summarize CARIBIC coordinators Dr. Carl Brenninkmeijer, MPI-C, and Dr. Andreas Zahn, KIT. The IAGOS-CARIBIC observatory was coordinated and operated by the MPI-C until the end of 2014, since then by the KIT....

Unknown 1830 painting of an eruption in Italy, a Wellcome Image, Wikimedia Commons, under the Creative Commons Attribution 4.0 International license

Catastrophic Chinese floods triggered by air pollution

Roland Pease at Science News: What atmospheric scientist Jiwen Fan saw on her television in July 2013 appalled her. The worst flooding to hit China in 50 years was happening in Sichuan province, in the same place that had been devastated by a massive earthquake just 5 years earlier. Over the course of 5 days, 73 centimeters of rain pounded the mountains, peaking at 29 centimeters in a single day. Rivers burst their banks and poured through city streets, washing away homes, factories, and bridges. Steep valley slopes collapsed in deadly landslides. About 200 people died, and a further 300,000 were displaced.

But Fan was worried about more than just the immediate effect of the floods. The Richland, Washington–based researcher—an expert on air pollution and climate at the Pacific Northwest National Laboratory in Richland, Washington—wondered how they had gotten so strong so fast. The Sichuan basin, surrounded by mountains that trap smoke billowing from its industrial centers, is “notorious” for its dirty air, she says. Did air pollution play a role? To find out, she and her team of Chinese, American, and Israeli researchers designed precision computer simulations to model what had happened.

Air pollution can affect precipitation in many ways. Sometimes, the aerosol particles in smoke can reduce or delay rain. Sometimes, they can make thunderstorms more intense. Their best understood interaction is in changing how water vapor condenses to form droplets in clouds. But Fan and her team have proposed a first: that pollution also changes some air circulation patterns that lead to rainclouds.

In the case of the Sichuan storms, they write in a paper published online before print in Geophysical Research Letters, soot in particular contributed to the catastrophic flooding. It prevented rainclouds from forming over the basin during the day, leading to more intense rainfall in the mountains that evening. “We were amazed at the scale of the effect the pollution had,” Fan says. “Effectively it redistributed the precipitation from the wide area of the basin into the mountains.”...

From the 2013 flooding in Sichuan, shot by 人神之间, Wikimedia Commons, under the  Creative Commons CC0 1.0 Universal Public Domain Dedication

Dust — and the microbes hitching rides on it — influences rain, climate

A press release from the American Chemical Society: Dusty air blowing across the Pacific from Asia and Africa plays a critical role in precipitation patterns throughout the drought-stricken western U.S. Today, a scientist will present new research suggesting that the exact chemical make-up of that dust, including microbes found in it, is the key to how much rain and snow falls from clouds throughout the region. This information could help better predict rain events, as well as explain how air pollution from a variety of sources influences regional climate in general.

...“We’ve learned that not all of the particles in the air at high altitudes have the same influence on clouds. We’re starting to think that these differences contribute to how rain gets distributed,” says Kim Prather, Ph.D.

Most of the dust that Prather’s team at the University of California, San Diego, detects in clouds and precipitation originates in Asian and Chinese deserts. It gets swept westward by the jet stream where it mixes with a variety of other airborne particles such as sea spray and smoke. Prather says that each of these types of particles — collectively known as aerosols — has its own, distinctive impact on clouds.

A major key to what turns ordinary clouds into rainmakers in the first place is their ability to form ice crystals around the microscopic particles that invade and “seed” them, Prather said. Without ice crystals as a catalyst, rain development inside clouds can be impaired.   “The standard belief is the more ice you have in a cloud, the more likely you will get precipitation out of it,” she says. “Our goal is to catch the first stages of ice forming and find out what exactly the chemical constituents are that the ice is forming on.”

...Prather speculates that the microbes hitch a ride on bits of sand, iron and other debris swept aloft from desert regions. Microbes and biological components could also become mixed with the dust as it is transported across the Pacific. She and her team are eager to learn just how important these bioparticles are in the rainmaking process.

...“Long term, our goal is to be able to predict how much precipitation we can expect to form when certain aerosols such as dust are coming toward us,” says Prather. “That’s a lofty goal but we’re making headway.”...

Via NASA, a satellite view of a dust cloud over Asia

Studying aerosols to improve climate models

Kimm Fesenmaier at Caltech News: Aerosols, tiny particles in the atmosphere, play a significant role in Earth's climate, scattering and absorbing incoming sunlight and affecting the formation and properties of clouds. Currently, the effect that these aerosols have on clouds represents the largest uncertainty among all influences on climate change.

But now researchers from Caltech and the Jet Propulsion Laboratory have provided a global observational study of the effect that changes in aerosol levels have on low-level marine clouds—the clouds that have the largest impact on the amount of incoming sunlight that Earth reflects back into space. The findings appear in the advance online version of the journal Nature Geoscience.

Changes in aerosol levels have two main effects—they alter the amount of clouds in the atmosphere and they change the internal properties of those clouds. Using measurements from several of NASA's Earth-monitoring satellites from August 2006 through April 2011, the researchers quantified for the first time these two effects from 7.3 million individual data points.

"If you combine these two effects, you get an aerosol influence almost twice that estimated in the latest report from the Intergovernmental Panel on Climate Change," says John Seinfeld, the Louis E. Nohl Professor and professor of chemical engineering at Caltech. "These results offer unique guidance on how warm cloud processes should be incorporated in climate models with changing aerosol levels."...

Mist in Sao Paolo, shot by Anagoria, Wikimedia Commons, under the Creative Commons 3.0 license 

No limits to human effects on clouds

The Press Room of the Weizmann Institute of Science (Israel): Understanding how clouds affect the climate has been a difficult proposition. What controls the makeup of the low clouds that cool the atmosphere or the high ones that trap heat underneath? How does human activity change patterns of cloud formation? The research of the Weizmann Institute’s Prof. Ilan Koren suggests we may be nudging cloud formation in the direction of added area and height. He and his team have analyzed a unique type of cloud formation; their findings, which appeared recently in Science indicate that in pre-industrial times, there was less cloud cover over areas of pristine ocean than is found there today.

Clouds need tiny particles called aerosols that rise in the atmosphere, in order to form. These aerosols – natural ones like sea salt or dust, or such human-made ones as soot – form nuclei around which the cloud droplets condense. In relatively clean environments, clouds can only grow as large as the amount of aerosols in the atmosphere allows: They will be the limiting factor in cloud formation.

The question is: Does the current load of aerosols in the atmosphere already exceed that limit, in which case adding extra particles should not greatly affect cloud form
ation; or do they continue to be a limiting factor as pollution rises, so that added aerosols would continue to influence the clouds? A model developed by Koren and his team showed that an increase in aerosols, even in relatively polluted conditions, should result in taller, larger clouds that rain more aggressively. ...

Koren, research student Guy Dagan and Dr. Orit Altaratz in the Earth and Planetary Sciences Department looked to an unlikely place to test their model: near the horse latitudes. These are subtropical regions far out in the oceans that were reviled in the past by sailors because the winds that carried their sails would die out there for weeks on end. Here was a lab for them to test the basic physics of their model: an atmospheric region controlled by well-defined meteorological conditions, which was sometimes pristine, sometimes containing low levels of aerosols. If the model was correct, transitions from one to the other should be dramatic. And they wanted to test their theory on the clouds that do form in this region – warm convective clouds that are fuelled by the ocean’s moisture.

...Koren: “We showed that convective clouds do not necessarily stop being aerosol-limited; under relatively polluted conditions the increase in aerosol loading will make the clouds taller, larger and their rain-rate stronger. As the area of this cloud cover grows, it reflects more of the shortwave radiation; but as the clouds get taller, their greenhouse effect becomes more significant, counteracting about half of their total cooling effect.”  

Convective clouds forming over the Amazon in a blanket of smoke. Image: Prof. Ilan Koren

Research clarifies health costs of air pollution from agriculture

A press release from NASA: Ammonia pollution from agricultural sources poses larger health costs than previously estimated, according to NASA-funded research.

Harvard University researchers Fabien Paulot and Daniel Jacob used computer models including a NASA model of chemical reactions in the atmosphere to better represent how ammonia interacts in the atmosphere to form harmful particulate matter. The improved simulation helped the scientists narrow in on the estimated health costs from air pollution associated with food produced for export – a growing sector of agriculture and a source of trade surplus.

"The 'cost' is an economic concept to measure how much people are willing to pay to avoid a risk," Paulot said. "This isused to quantify the cost for society but also to evaluate the benefits of mitigation."

The new research by Paulot and Jacob calculate the health cost associated with the ammonia emissions from agriculture exports to be $36 billion a year – equal to about half of the revenue generated by those same exports – or $100 per kilogram of ammonia. The study was published December 2013 in Environmental Science & Technology.

The new estimate is about double the current estimate by the U.S. Environmental Protection Agency, which suggests a cost of $47 per kilogram of ammonia. The scientists say the new estimate is on the high end of the spectrum, which reflects the need for more research into characterizing the relationship between agricultural ammonia emissions and the formation of the harmful fine particulate matter – a relationship that's not as straightforward as previous estimates assumed.

"The effect of ammonia on fine particulate is complex, and we believe that the models previously used in the United States to price ammonia emissions have not captured this well," Paulot said.

The map shows increase in annual mean surface concentration of particulate matter resulting from ammonia emissions associated with food export. Populated states in the Northeast and Great Lakes region, where particulate matter formation is promoted by upwind ammonia sources, carry most of the cost.

Famous paintings help global warming experts track climate change over the decades

James Maynard in Tech Times: Paintings from J.M.W. Turner and other artists are being used to track how pollution levels may have changed over time. Investigators are examining what vivid sunrises and sunsets painted by artists could tell us about the environmental effects of volcanic eruptions.

William Turner was born in England in 1775, and lived until 1851. He is best known as a landscape artist, including a wide variety of sunset paintings. The Lake, Petworth sunset, fighting bucks by the artist is one of the paintings investigators examined to clues to ancient eruptions.  In 1815, the Tambora Volcano in Indonesia erupted, spewing thousands of tons of debris into the air. Much of this material traveled around the road, making sunsets and sunrises redder and more dramatic.

Christos Zerefos, from the Academy of Athens in Greece, led the investigation.  "Nature speaks to the hearts and souls of great artists. But we have found that, when coloring sunsets, it is the way their brains perceive greens and reds that contains important environmental information," Zerefos told the press.

Researchers studied 554 paintings of sunsets created between 1500 and 2000. A total of 181 artists created the art works, including Rembrandt, Hogarth, Gainsborough, and Rubens.  "We found that red-to-green ratios measured in the sunsets of paintings by great masters correlate well with the amount of volcanic aerosols in the atmosphere, regardless of the painters and of the school of painting," Zerefos explained.

Greater than normal levels of red predominated in areas affected by volcanic ash, study says. This allows a way of measuring the aerosol optical depth, a total of all the dust, ash and other particulate matter in the atmosphere at a given time....

Turner's "Petworth Park"

Long-term warming likely to be significant despite recent slowdown

NASA-Goddard Space Center: A new NASA study shows Earth's climate likely will continue to warm during this century on track with previous estimates, despite the recent slowdown in the rate of global warming.

This research hinges on a new and more detailed calculation of the sensitivity of Earth's climate to the factors that cause it to change, such as greenhouse gas emissions. Drew Shindell, a climatologist at NASA's Goddard Institute for Space Studies in New York, found Earth is likely to experience roughly 20 percent more warming than estimates that were largely based on surface temperature observations during the past 150 years. Shindell's paper on this research was published March 9 in the journal Nature Climate Change.

Global temperatures have increased at a rate of 0.22 Fahrenheit (0.12 Celsius) per decade since 1951. But since 1998, the rate of warming has been only 0.09 F (0.05 C) per decade -- even as atmospheric carbon dioxide continues to rise at a rate similar to previous decades. Carbon dioxide is the most significant greenhouse gas generated by humans.

Some recent research, aimed at fine-tuning long-term warming projections by taking this slowdown into account, suggested Earth may be less sensitive to greenhouse gas increases than previously thought. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), which was issued in 2013 and was the consensus report on the state of climate change science, also reduced the lower range of Earth's potential for global warming.

...Shindell's paper further focuses on improving our understanding of how airborne particles, called aerosols, drive climate change in the Northern Hemisphere. Aerosols are produced by both natural sources – such as volcanoes, wildfire and sea spray – and sources such as manufacturing activities, automobiles and energy production. Depending on their make-up, some aerosols cause warming, while others create a cooling effect. In order to understand the role played by carbon dioxide emissions in global warming, it is necessary to account for the effects of atmospheric aerosols.

While multiple studies have shown the Northern Hemisphere plays a stronger role than the Southern Hemisphere in transient climate change, this had not been included in calculations of the effect of atmospheric aerosols on climate sensitivity. Prior to Shindell's work, such calculations had assumed aerosol impacts were uniform around the globe....

A new NASA study suggests that projections of Earth's future warming should be more in line with previous estimates that indicated a higher sensitivity to increasing greenhouse gas emissions. Image Credit: NASA SVS/NASA Center for Climate Simulation

Volcanoes contribute to recent warming ‘hiatus’

Alli Gold Roberts in MIT News: By the late 1990s, scientists had observed more than two decades of rapid global warming, and expected the warming trend to continue. Instead, despite continuing increases in greenhouse gas emissions, the Earth’s surface temperatures have remained nearly flat for the last 15 years. The International Panel on Climate Change verified this recent warming “hiatus” in its latest report.

Researchers around the globe have been working to understand this puzzle — looking at heat going into the oceans, changes in wind patterns, and other factors to explain why temperatures have stayed nearly stable, while greenhouse gas concentrations have continued to rise. In a study published today in Nature Geoscience, a team of scientists from MIT and elsewhere around the U.S. report that volcanic eruptions have contributed to this recent cooling, and that most climate models have not accurately accounted for the effects of volcanic activity.

“This is the most comprehensive observational evaluation of the role of volcanic activity on climate in the early part of the 21st century,” says co-author Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT. “We assess the contributions of volcanoes on temperatures in the troposphere — the lowest layer of the atmosphere — and find they’ve certainly played some role in keeping the Earth cooler.”

There are many components of the Earth’s climate system that can increase or decrease the temperature of the globe. For example, while greenhouse gases cause warming, some types of small particles, known as aerosols, cause cooling. When volcanoes erupt explosively enough, they enhance these aerosols — a phenomenon referred to as “volcanic forcing.”...

A 2002 eruption of Mt. Etna viewed from the International Space Station

Anthropogenic aerosols caused global temperature drop in 1950s

Nadya Anscombe in Environmental Research Web: More than 50% of the decrease in global mean near-surface temperature observed between 1950 and 1965 was due to anthropogenic aerosols, according to researchers in the UK.

Laura Wilcox and colleagues of the University of Reading and the Met Office used the most recent climate models to confirm that aerosols played a large role in the temperature decrease in that timeframe. They have, for the first time, quantified the size of the contribution made by anthropogenic aerosols, as opposed to natural aerosols.

“The idea that aerosols cause cooling is not new,” Wilcox told environmentalresearchweb. “Previous work with single models has suggested that it is the indirect effect of aerosols – their interaction with clouds – that accounts for most of their cooling influence. We have shown this to be the case for multiple models. Without the indirect effect, the models are unable to reproduce the cooling in the 1950s and 1960s. By running the models with all climate-forcing agents fixed, except anthropogenic aerosols, we have for the first time been able to quantify the contribution of anthropogenic aerosols.”

The results, said Wilcox, are striking. “Even in such a short timeframe, and taking into account the uncertainties in the models we used, the evidence is clear – anthropogenic aerosols were the main contributor to the global mean temperature drop between 1950–1965,” she said. “Aerosols could have a more significant effect on global mean temperature than greenhouse gases, and with anthropogenic aerosols expected to decrease in the coming years, our findings have implications for future policy.”

The research also showed that the cooling effect of anthropogenic aerosols on temperature is so great that it cancelled out the warming effects due to greenhouse gases to give an overall global cooling between 1950 and 1965....

Aerosol pollution over India in 2001, shot by NASA

Climate science boost with more accurate profile of tropical aerosols

CSIRO (Australia): The seasonal influence of aerosols on Australia's tropical climate can now be included in climate models following completion of the first long-term study of fine smoke particles generated by burning of the savanna open woodland and grassland.

Australia's biomass burning emissions comprise about eight per cent of the global total, ranking third by continent behind Africa (48 per cent) and South America (27 per cent).

Lead researcher, CSIRO's Dr Ross Mitchell, said fine particles generated by burning of the tropical savanna of Northern Australia are a globally significant aerosol source, with impacts on regional climate and air quality.

"Aerosols play a very important role in modulating climate, yet the knowledge of perhaps the most basic piece of information - the seasonal climatology - remains undetermined for many aerosol producing regions.

...."This foundation stone of the aerosol cycle allows hard-nosed testing and development of the aerosol modules used within global climate models," Dr Mitchell said...

Bush fire in central Queensland, shot by 80 trading 24, Wikimedia Commons, nder the Creative Commons Attribution-Share Alike 3.0 Unported license

NASA to study how pollution, storms and climate mix

Space Daily via SPX: NASA aircraft will take to the skies over the southern United States this summer to investigate how air pollution and natural emissions, which are pushed high into the atmosphere by large storms, affect atmospheric composition and climate.

NASA will conduct its most complex airborne science campaign of the year from Houston's Ellington Field, which is operated by the agency's Johnson Space Center, beginning Aug. 7 and continuing through September. The field campaign draws together coordinated observations from NASA satellites, aircraft and an array of ground sites.

More than 250 scientists, engineers and flight personnel, including several from NASA's Jet Propulsion Laboratory, Pasadena, Calif., are participating in the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. The project is sponsored by the Earth Science Division in the Science Mission Directorate at NASA Headquarters in Washington. Brian Toon of the Department of Atmospheric and Oceanic Sciences at the University of Colorado, Boulder, is the lead scientist.

Aircraft and sensors will probe the atmosphere from top to bottom at the critical time of year when weather systems are strong enough and regional air pollution and natural emissions are prolific enough to pump gases and particles high into the atmosphere. The result is potentially global consequences for Earth's atmosphere and climate.

"In summertime across the United States, emissions from large seasonal fires, metropolitan areas and vegetation are moved upward by thunderstorms and the North American Monsoon," Toon said. "When these chemicals get into the stratosphere they can affect the whole Earth. They also may influence how thunderstorms behave. With SEAC4RS we hope to better understand how all these things interact."

The campaign will provide new insights into the effects of the gases and tiny aerosol particles in the atmosphere. The mission is targeting two major regional sources of summertime emissions: intense smoke from forest fires in the U.S. West and natural emissions of isoprene, a carbon compound, from forests in the Southeast....

Aftermath of the Bastrop, Texas, fires in October 2011, shot by Ed Schipul, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license

Plants moderate climate warming

The International Institute for Applied Systems Analysis: As temperatures warm, plants release gases that help form clouds and cool the atmosphere, according to research from IIASA and the University of Helsinki.

The new study, published in Nature Geoscience, identified a negative feedback loop in which higher temperatures lead to an increase in concentrations of natural aerosols that have a cooling effect on the atmosphere. “Plants, by reacting to changes in temperature, also moderate these changes,” says IIASA and University of Helsinki researcher Pauli Paasonen, who led the study.

Scientists had known that some aerosols – particles that float in the atmosphere – cool the climate as they reflect sunlight and form cloud droplets, which reflect sunlight efficiently. Aerosol particles come from many sources, including human emissions. But the effect of so-called biogenic aerosol – particulate matter that originates from plants – had been less well understood. Plants release gases that, after atmospheric oxidation, tend to stick to aerosol particles, growing them into the larger-sized particles that reflect sunlight and also serve as the basis for cloud droplets. The new study showed that as temperatures warm and plants consequently release more of these gases, the concentrations of particles active in cloud formation increase.

“Everyone knows the scent of the forest,” says Ari Asmi, University of Helsinki researcher who also worked on the study. “That scent is made up of these gases.” While previous research had predicted the feedback effect, until now nobody had been able to prove its existence except for case studies limited to single sites and short time periods. The new study showed that the effect occurs over the long-term in continental size scales.

The effect of enhanced plant gas emissions on climate is small on a global scale – only countering approximately 1 percent of climate warming, the study suggested. “This does not save us from climate warming,” says Paasonen. However, he says, “Aerosol effects on climate are one of the main uncertainties in climate models. Understanding this mechanism could help us reduce those uncertainties and make the models better.”

The study also showed that the effect was much larger on a regional scale, counteracting possibly up to 30% of warming in more rural, forested areas where anthropogenic emissions of aerosols were much lower in comparison to the natural aerosols. That means that especially in places like Finland, Siberia, and Canada this feedback loop may reduce warming substantially....

Misty Forest. Looking across to Gale Hill Point from the Roman road. Shot by Steve Partridge, Wikimedia Commons via Geograph UK, under the Creative Commons Attribution-Share Alike 2.0 Generic license

Aerosols confirmed rising over India

T.V. Padma in SciDev.net: While satellite data has shown aerosols — tiny polluting particles in the air — to be rising over India, a new study based on primary data gathered from measuring instruments installed in a network of stations confirms the trend.

The study, by a team from the Vikram Sarabhai Space Centre, Thiruvananthapuram, and Indian Institute of Science (IISc), Bangalore, published online in Geophysical Research Letters last month (14 March), is based on the principle that aerosols absorb the sun's rays as they reach the earth's surface.

The amount of aerosols in the air can be measured as aerosol optical density (AOD). A 2011 study, reported in Atmospheric Environment, also found a rising trend in AOD based on data gathered from two US satellites.

But, satellite data often do not give reliable estimates due to cloud formation, different degrees of reflection off different types of surfaces and erroneous interpretation of noises and biases in aerosols as legitimate signals, scientists observed.

The new Indian study offers primary data gathered from instruments measuring solar radiation at 380—1025 nanometres in wavelength at 35 locations across the country...

A burning warehouse in Kolkata, shot by Biswarup Ganguly, Wikimedia Commons, under the Creative Commons Attribution 3.0 Unported license

Saharan and Asian dust, biological particles end global journey in California

Scripps News at the Scripps Institution of Oceanography: A field study of aerosol impacts on clouds and precipitation in the Sierra Nevada shows that dust and microorganisms transported from as far away as the Sahara desert help to spur the precipitation that California counts on for its water supply.

The CalWater field campaign, funded by the California Energy Commission and led by UC San Diego and NOAA, could help western states better understand the future of their water supply and hydropower generation as climate change influences how much and how often dust travels around the world and alters precipitation far from its point of origin.

"UC San Diego is a leader in addressing complex, multi-disciplinary global challenges, such as water shortages and environmental concerns," said UCSD Chancellor Pradeep K. Khosla. "Our researchers work collaboratively to investigate and produce meaningful and impactful research that will further our understanding of our planet and environment, so we can improve human life and our world."

Jessie Creamean, a postdoctoral associate at NOAA's Earth System Research Laboratory in Boulder, Colo., co-authored the paper appearing in the journal Science with Kaitlyn Suski, a graduate student in the laboratory of Distinguished Chair in Atmospheric Chemistry Prof. Kimberly Prather, who holds appointments at Scripps Institution of Oceanography and the Department of Chemistry and Biochemistry at UCSD.

"We were able to show dust and biological aerosols that made it from as far as the Sahara were incorporated into the clouds to form ice, then influenced the formation of the precipitation in California," said Creamean, who conducted the fieldwork as a UCSD graduate student under Prather, the study leader. "To our knowledge, no one has been able to directly determine the origin of the critical aerosols seeding mid-level clouds which ultimately produce periods with extensive precipitation typically in the form of snow at the ground."...

From NASA: Saharan sand blowing off the coasts of Mauritania and Senegal

Climate change: aging of organic aerosols is caused by OH radicals

Science Daily: Atmospheric aerosol particles have a significant effect on climate. An international team of researchers has now discovered that a chemical process in the atmosphere called aging determines to a major extent the concentration and the characteristics of aerosol particles. To date, this aspect has not been accounted for in regional and global climate models. In the Muchachas [Multiple Chamber Aerosol Chemical Aging Experiments] project, the team has not only managed to demonstrate the effects of aging but has also been able to measure these.

...The quality of air is determined to a considerable extent by aerosol particles. In the form of a fine dust, they are believed to be responsible for a series of respiratory diseases and cardiovascular disorders. In addition, aerosol particles also have various effects on atmospheric radiation balance. Aerosols make a direct contribution to radiation levels in the cloud-free atmosphere by dispersing, reflecting, and absorbing sunlight. Aerosols are also essential for cloud formation in the troposphere: They act as condensation nuclei which even in the presence of low levels of water vapor do enable droplets to form.

The size and concentration of aerosol particles is also of great importance for the number of cloud drops, which in turn influences the reflection characteristics of clouds. Hence, aerosol particles tend to have a cooling influence on the atmosphere. However, the precise processes and feedback mechanisms have not yet been fully understood, so that the interaction between aerosol particles, their suitability as cloud condensation nuclei, and the sunlight reflected off Earth's surface represented one of the greatest uncertainties in the calculation of climatic activity.

The Muchachas project looked at organic aerosols, which constitute the largest proportion of chemical airborne particles. Organic aerosols are generated above forests, for example, and they are visible in the form of a blue mist in certain places such as the Great Smoky Mountains, the Blue Ridge Mountains, and the Blue Mountains. In densely populated areas however, anthropogenically generated and released hydrocarbons play an important role as precursor of the development of secondary organic aerosols....

Mist rising from the Blue Ridge Mountains, shot by Jürgen Nagel (Jürgen Nagel), Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Atmospheric heating by black carbon aerosol re-evaluated

R&D: Viewed as a potential target in the global effort to reduce climate change, atmospheric black carbon particles absorb significantly less sunlight than scientists predicted, raising new questions about the impact of black carbon on atmospheric warming, an international team of researchers, including climate chemists from Boston College, report today in the latest edition of the journal Science.
   
Mathematical models and laboratory experiments used to study airborne soot particles led to projections that the absorption-boosting chemicals that coat black carbon could yield an increase in absorption by as much as a factor of two. But field studies in smoggy California cities found black carbon absorption enhancements of just 6%, suggesting that climate models may be overestimating warming by black carbon, the researchers report.
   
The surprising results highlight the early challenges in a nascent sector of climate science and could have implications for regulatory efforts to reduce the production of black carbon, or soot, by curbing the burning of fossil fuels. Still, scientists agree that black carbon in the atmosphere has a significant effect on global and regional climate, with earlier studies ranking the warming effects of black carbon particles second only to carbon dioxide gas….

Air pollution belches from a truck, shot by Zakysant and modified by F. Lamiot, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Pine trees one of biggest contributors to air pollution: pine gases chemically transformed by free radicals

Science Daily: Pine trees are one of the biggest contributors to air pollution. They give off gases that react with airborne chemicals -- many of which are produced by human activity -- creating tiny, invisible particles that muddy the air. New research from a team led by Carnegie Mellon University's Neil Donahue shows that the biogenic particles formed from pine tree emissions are much more chemically interesting and dynamic than previously thought. The study provides the first experimental evidence that such compounds are chemically transformed by free radicals, the same compounds that age our skin, after they are first formed in the atmosphere.

These findings, published in the Proceedings of the National Academy of Sciences, can help make climate and air quality prediction models more accurate, and enable regulatory agencies to make more effective decisions as they consider strategies for improving air quality.

"We have been able to show conclusively that biogenics are chemically transformed in the atmosphere. They're not just static. They keep going, they keep changing and they keep growing," said Donahue, professor of chemistry, chemical engineering, engineering and public policy, and director of Carnegie Mellon's Center for Atmospheric Particle Studies. "Quite a few atmospheric models, which are commonly used to inform research and policy, have been assuming that that doesn't happen. What we really need to have in the models is an accurate representation of what's really going on in the atmosphere, and that's what this lets us do."

The air that we breathe is chock-full of particles called aerosols. These tiny liquid or solid particles come from hundreds of sources including trees, volcanoes, cars, trucks and wood fires. The small particles influence cloud formation and rainfall, and affect climate and human health. In the United States each year, 50,000 premature deaths from heart and lung disease are attributable to excess concentrations of aerosols, especially particles less than 2.5 micrometers in diameter.

"There's a very, very strong body of data that establishes that fine particles in the air we breathe have a significant bad effect on people. What is less well understood is how the size and chemical composition of those particles influences that effect," Donahue said....

A pine near Lake Tahoe, shot by Brewbooks at Flickr, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license

Exploring one of climate's 'known unknowns' -- aerosols

Terra Daily via SPX: The influence of aerosols (small particles less than 1 micrometre in diameter) and clouds (liquid droplets 1 - 1000 micrometres diameter) represents one of the largest uncertainties in our understanding of trends in past global climate and predicting future climate change, as recognised by the 2007 report of the Intergovernmental Panel on Climate Change.

One of the most significant 'known unknowns' is how quickly water can condense on the small aerosol particles to grow and become cloud droplets, influencing the albedo (reflectivity) of clouds and cloud lifetime (precipitation).

In a study published in PNAS, Professor Jonathan Reid of the University of Bristol and colleagues show that the rate of cloud droplet growth can be strongly dependent on the composition of the aerosol.

For aerosol particles that have high viscosity (equivalent to saying they behave like treacle or even bitumen), water evaporation and condensation can be very slow, taking many hours.

For particles that are much less viscous (more like olive oil or even water), evaporation and condensation can be very fast: less than 1 second....

The view from Dornbirn in Austria towards Oberfallenberg in Switzerland, a beautiful shot by böhringer friedrich, Wikimedia Commons, böhringer friedrich

"Warming hole" delayed climate change over eastern United States

Harvard University: Climate scientists at the Harvard School of Engineering and Applied Sciences (SEAS) have discovered that particulate pollution in the late 20th century created a "warming hole" over the eastern United States—that is, a cold patch where the effects of global warming were temporarily obscured.

While greenhouse gases like carbon dioxide and methane warm the Earth's surface, tiny particles in the air can have the reverse effect on regional scales. "What we've shown is that particulate pollution over the eastern United States has delayed the warming that we would expect to see from increasing greenhouse gases," says lead author Eric Leibensperger (Ph.D. '11), who completed the work as a graduate student in applied physics at SEAS.

"For the sake of protecting human health and reducing acid rain, we've now cut the emissions that lead to particulate pollution," he adds, "but these cuts have caused the greenhouse warming in this region to ramp up to match the global trend." At this point, most of the "catch-up" warming has already occurred.

The findings, published in the journal Atmospheric Chemistry and Physics, present a more complete picture of the processes that affect regional climate change. The work also carries significant implications for the future climate of industrial nations, like China, that have not yet implemented air quality regulations to the same extent as the United States.

Until the United States passed the Clean Air Act in 1970 and strengthened it in 1990, particulate pollution hung thick over the central and eastern states. Most of these particles in the atmosphere were made of sulfate, originating as sulfur emissions from coal-fired power plants. Compared to greenhouse gases, particulate pollution has a very short lifetime (about 1 week), so its distribution over the Earth is uneven....

Observed change in surface air temperature between 1930 and 1990. Observations are from the NASA GISS Surface Temperature Analysis. Image courtesy of Eric Leibensperger, from the Harvard website