OREGON STATE UNIVERSITY

college of earth

Climate center at OSU gets major grant to study forest mortality

CORVALLIS, Ore. – Oregon State University has received a five-year, $4 million grant from the United States Department of Agriculture to investigate increasing impacts of drought, insect attacks and fires on forests in the western U.S., and to project how the influence of climate change may affect forest die-offs in the future.

The researchers will also enhance an earth system model to allow them to predict when forests are becoming vulnerable to physiological stress and then create strategies to minimize impacts of climate, insects and fire.

“The western United States has gone through two decades of devastating forest loss and we don’t even fully know why it happened, much less how to predict these events,” said Philip Mote, director of the Oregon Climate Change Research Institute at OSU and a principal investigator on the grant. “Certainly wildfire, bark beetle infestation and drought play a role, but the intersection of these factors with forest management decisions hasn’t been well-explored.

“A change in severity of drought, for example, can make the difference between trees losing some needles and wiping out the entire stand,” added Mote, a professor in the College of Earth, Ocean, and Atmospheric Sciences at OSU. “The margin between life and death in the forest can be rather small.”

Other lead investigators from OSU on the project include Beverly Law, a professor in the Department of Forest Ecosystems and Society, who will focus on modeling forest processes with the Community Land Model; and Andrew Plantinga, a professor in the Department of Applied Economics, whose expertise is on the economics of land use, climate change and forests.

“Climate variation and extremes can impact trees differently depending on species-specific traits that determine how they compete and respond to environmental conditions,” Law said. “We know little about how physiological limits vary by species, and have not incorporated such knowledge in earth system models.”

The OSU researchers note that forest management decisions could potentially play a role during periods of drought, for example. Drought-stressed trees become vulnerable when they experience vapor pressure deficits – and cannot take in enough water to sustain them, or to remain vigorous enough to help repel invading bark beetles, said Law, who is co-lead principal investigator on the project.

An excess of trees in an area of limited water might benefit from targeted thinning so fewer trees remain to compete for the same amount of water, Law noted. However, forests that already have low densities “are not expected to respond well,” she said.

“What we don’t know,” Mote said, “is what the threshold is between stress and mortality, which trees to thin and how many, and whether such a strategy not only works, but is economically feasible for landowners.”

Law said the intervention strategies “should not result in potentially harmful ecological impacts on habitat and soil quality.”

Among the goals of the project are to:

  • Improve the ability of a leading land surface model to predict tree mortality;
  • Map the vulnerability of western forests to mortality under present and future climate conditions,  particularly in Oregon, Washington, California and Idaho;
  • Apply forest vulnerability data to forest sector models to help land managers better predict ecological and economic outcomes, including timber production, forest recreation and water use.

As part of the study, the researchers will run computer models that will utilize a crowd-sourced computing effort called Weatherathome.net, through which a network of thousands of volunteers will use their home computers to run climate model scenarios. Such a network can equal or exceed the output of a supercomputer.

The OSU grant is part of the inter-agency Decadal and Regional Climate Prediction Using Earth System Models Program, which is coordinated by the National Science Foundation and includes USDA and the Department of Energy.

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Phil Mote, 541-737-5694

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Dying trees

Forest die-off

Global warming to cut snow water storage 56 percent in Oregon watershed

The study this story is based on is available online: http://bit.ly/13ZLzl1

CORVALLIS, Ore. – A new report projects that by the middle of this century there will be an average 56 percent drop in the amount of water stored in peak snowpack in the McKenzie River watershed of the Oregon Cascade Range -  and that similar impacts may be found on low-elevation maritime snow packs around the world.

The findings by scientists at Oregon State University, which are based on a projected 3.6 degree Fahrenheit temperature increase, highlight the special risks facing many low-elevation, mountainous regions where snow often falls near the freezing point. In such areas, changing from snow to rain only requires a very modest rise in temperature.

As in Oregon, which depends on Cascade Range winter snowpack for much of the water in the populous Willamette Valley, there may be significant impacts on ecosystems, agriculture, hydropower, industry, municipalities and recreation, especially in summer when water demands peak.

The latest study was one of the most precise of its type done on an entire watershed, and was just published in Hydrology and Earth System Sciences, with support from the National Science Foundation. It makes it clear that new choices are coming for western Oregon and other regions like it.

“In Oregon we have a water-rich environment, but even here we will have to manage our water resources differently in the future,” said Eric Sproles, who led this study as a doctoral student at OSU.

“In the Willamette River, for instance, between 60-80 percent of summer stream flow comes from seasonal snow above 4,000 feet,” he said. “As more precipitation falls as rain, there will more chance of winter flooding as well as summer drought in the same season. More than 70 percent of Oregon’s population lives in the Willamette Valley, with the economy and ecosystems depending heavily on this river.”

Annual precipitation in the future may be either higher or lower, the OSU researchers said. They did calculations for precipitation changes that could range 10 percent in either direction, although change of that magnitude is not anticipated by most climate models.

The study made clear, so far as snowpack goes, that temperature is the driving force, far more than precipitation. Even the highest levels of anticipated precipitation had almost no impact on snow-water storage, they said.

“This is not an issue that will just affect Oregon,” said Anne Nolin, a professor in the College of Earth, Ocean, and Atmospheric Sciences, and co-author of the study. “You may see similar impacts almost anywhere around the world that has low-elevation snow in mountains, such as in Japan, New Zealand, Northern California, the Andes Mountains, a lot of Eastern Europe and the lower-elevation Alps.”

The focus of this study was the McKenzie River, a beautiful, clear mountain river that rises in the high Cascade Range near the Three Sisters volcanoes, and supplies about 25 percent of the late summer discharge of the Willamette River. Researchers said this is one of the most detailed studies of its type done on a large watershed.

Among the findings of the study:

  • The average date of peak snowpack in the spring on this watershed will be about 12 days earlier by the middle of this century.
  • The elevation zone from 1,000 to 1,500 meters will lose the greatest volume of stored water, and some locations at that elevation could lose more than 80 days of snow cover in an average year.
  • Changes in dam operations in the McKenzie River watershed will be needed, but will not be able to make up for the vast capability of water storage in snow.
  • Summer water flows will be going down even as Oregon’s population surges by about 400,000 people from 2010 to 2020.
  • Globally, maritime snow comprises about 10 percent of the Earth’s seasonal snow cover.
  • Snowmelt is a source of water for more than one billion people.
  • Precipitation is highly sensitive to temperature and can fall as rain, snow, or a rain-snow mix.

The model developed for this research, scientists said, could be readily adapted to help other regions in similar situations determine their future loss of snow water in the future.

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Eric Sproles, 541-729-1377

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McKenzie River watershed

McKenzie River watershed


McKenzie River

McKenzie River

Study explains Pacific equatorial cold water region

CORVALLIS, Ore. – A new study published this week in the journal Nature reveals for the first time how the mixing of cold, deep waters from below can change sea surface temperatures on seasonal and longer timescales.

Because this occurs in a huge region of the ocean that takes up heat from the atmosphere, these changes can influence global climate patterns, particularly global warming.

Using a new measurement of mixing, Jim Moum and Jonathan Nash of the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University have obtained the first multi-year records of mixing that permit assessment of seasonal changes. This is a significant advance beyond traditional shipboard measurements that are limited to the time that a ship can be away from port. Small instruments fueled by lithium batteries were built to be easily deployed on deep-sea equatorial moorings.

Moum employs a simple demonstration to show how mixing works.

He pours cold, white cream into a clear glass mug full of hot, black coffee, very carefully, using a straw to inject the heavier cream at the bottom of the mug, where it remains.

“Now we can wait until the cream diffuses into the coffee, and we’ll have a nice cuppa joe,” Moum says. “Unfortunately, the coffee will be cold by then. Or, we can introduce some external energy into the system, and mix it.”

A stirring spoon reveals motions in the mug outlined by the black/white contrasts of cream in coffee until the contrast completely disappears, and the color achieves that of café au lait.

“Mixing is obviously important in our normal lives, from the kitchen to the dispersal of pollutants in the atmosphere, reducing them to levels that are barely tolerable,” he said.

The new study shows how mixing, at the same small scales that appear in your morning coffee, is critical to the ocean. It outlines the processes that create the equatorial Pacific cold tongue, a broad expanse of ocean near the equator that is roughly the size of the continental United States, with sea surface temperatures substantially cooler than surrounding areas.

Because this is a huge expanse that takes up heat from the atmosphere, understanding how it does so is critical to seasonal weather patterns, El Nino, and to global climate change.

In temperate latitudes, the atmosphere heats the ocean in summer and cools it in winter. This causes a clear seasonal cycle in sea surface temperature, at least in the middle of the ocean. At low latitudes near the equator, the atmosphere heats the sea surface throughout the year. Yet a strong seasonal cycle in sea surface temperature is present here, as well. This has puzzled oceanographers for decades who have suspected mixing may be the cause but have not been able to prove this.

Moum, Nash and their colleagues began their effort in 2005 to document mixing at various depths on an annual basis, which previously had been a near-impossible task.

“This is a very important area scientifically, but it’s also quite remote,” Moum said. “From a ship it’s impossible to get the kinds of record lengths needed to resolve seasonal cycles, let alone processes with longer-term cycles like El Nino and La Nina. But for the first time in 2005, we were able to deploy instrumentation to measure mixing on a NOAA mooring and monitor the processes on a year-round basis.”

The researchers found clear evidence that mixing alone cools the sea surface in the cold tongue, and that the magnitude of mixing is influenced by equatorial currents that flow from east to west at the surface, and from west to east in deeper waters 100 meters beneath the surface.

“There is a hint – although it is too early to tell – that increased mixing may lead, or have a correlation to the development of La Niña,” Moum said. “Conversely, less mixing may be associated with El Niño. But we only have a six-year record – we’ll need 25 years or more to reach any conclusions on this question.”

Nash said the biggest uncertainty in climate change models is understanding some of the basic processes for the mixing of deep-ocean and surface waters and the impacts on sea surface temperatures. This work should make climate models more accurate in the future.

The research was funded by the National Science Foundation, and deployments have been supported by the National Oceanic and Atmospheric Administration. Continued research will add instruments at the same equatorial mooring and an additional three locations in the equatorial Pacific cold tongue to gather further data.

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Jim Moum, 541-737-2553

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Ocean buoy

Buoy at sea

New study finds “nighttime heat waves” increasing in Pacific Northwest

CORVALLIS, Ore. – A new study has found that heat waves are increasing in the western portions of the Pacific Northwest, but not the kind most people envision, with scorching hot days of temperatures reaching triple digits.

These heat waves occur at night.

Researchers documented 15 examples of “nighttime heat waves” from 1901 through 2009 and 10 of those have occurred since 1990. Five of them took place during a four-year period from 2006-09. And since the study was accepted for publication in the Journal of Applied Meteorology and Climatology, another nighttime heat wave took place at the end of this June, the authors point out.

“Most people are familiar with daytime heat waves, when the temperatures get into the 100s and stay there for a few days,” said Kathie Dello, deputy director of the Oregon Climate Service at Oregon State University and a co-author on the study. “A nighttime heat wave relates to how high the minimum temperature remains overnight.

“Daytime events are usually influenced by downslope warming over the Cascade Mountains, while nighttime heat waves seem to be triggered by humidity,” said Dello, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “Elevated low-level moisture at night tends to trap the heat in.”

In their study, Dello and co-authors Karin Bumbaco and Nicholas Bond from the University of Washington defined heat waves as three consecutive days of temperatures at the warmest 1 percentile over the past century. Using that standard criterion, they documented 13 examples of daytime heat waves during the time period from 1901 to 2009. Only two of those occurred in the last 20 years.

In contrast, nighttime heat waves have been clustered over the past two decades, with what appears to be accelerating frequency. A warming climate suggests the problem may worsen, studies suggest.

“If you look at nighttime temperatures in Oregon and compared them to say the Midwest, people there would laugh at the concept of a Pacific Northwest heat wave,” Dello said. “However, people in the Midwest are acclimated to the heat while in the Northwest, they are not. People in other regions of the country may also be more likely to have air conditioning in their homes.

On occasion, daytime and nighttime heat waves coincide, Dello said, as happened in 2009 when temperatures in the Pacific Northwest set all-time records in Washington (including 103 degrees at SeaTac), and temperatures in Oregon surpassed 105 degrees in Portland, Eugene, Corvallis and Medford. It was the second most-intense daytime heat wave in the last century, but lasted only three days by the 1 percentile definition.

However, that same stretch of hot weather in 2009 results in a nighttime heat wave that extended eight days, by far the longest stretch since records were kept beginning in 1901.

The latest nighttime heat wave began in late June of this year, and continued into early July, Dello said.

“Like many nighttime heat waves, a large high-pressure ridge settled in over the Northwest, while at the same time, some monsoonal moisture was coming up from the Southwest,” she pointed out. “The high swept around and grabbed enough moisture to elevate the humidity and trap the warm air at night.”

Dello frequently provides weather facts and historical data via Twitter at: www.twitter.com/orclimatesvc.

The Oregon Climate Change Research Institute is supported by the state of Oregon, U.S. Department of the Interior, National Oceanic and Atmospheric Association, and other agencies.

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Kathie Dello, 541-737-8927

Scientists outline long-term sea-level rise in response to warming of planet

CORVALLIS, Ore. – A new study estimates that global sea levels will rise about 2.3 meters, or more than seven feet, over the next several thousand years for every degree (Celsius) the planet warms.

This international study is one of the first to combine analyses of four major contributors to potential sea level rise into a collective estimate, and compare it with evidence of past sea-level responses to global temperature changes.

Results of the study, funded primarily by the National Science Foundation and the German Federal Ministry of Education and Research, are being published this week in the Proceedings of the National Academy of Sciences.

“The study did not seek to estimate how much the planet will warm, or how rapidly sea levels will rise,” noted Peter Clark, an Oregon State University paleoclimatologist and author on the PNAS article. “Instead, we were trying to pin down the ‘sea-level commitment’ of global warming on a multi-millennial time scale. In other words, how much would sea levels rise over long periods of time for each degree the planet warms and holds that warmth?”

“The simulations of future scenarios we ran from physical models were fairly consistent with evidence of sea-level rise from the past,” Clark added. “Some 120,000 years ago, for example, it was 1-2 degrees warmer than it is now and sea levels were about five to nine meters higher. This is consistent with what our models say may happen in the future.”

Scientists say the four major contributors to sea-level rise on a global scale will come from melting of glaciers, melting of the Greenland ice sheet, melting of the Antarctic ice sheet, and expansion of the ocean itself as it warms. Several past studies have examined each of these components, the authors say, but this is one of the first efforts at merging different analyses into a single projection.

The researchers ran hundreds of simulations through their models to calculate how the four areas would respond to warming, Clark said, and the response was mostly linear. The amount of melting and subsequent sea-level response was commensurate with the amount of warming. The exception, he said, was in Greenland, which seems to have a threshold at which the response can be amplified.

“As the ice sheet in Greenland melts over thousands of years and becomes lower, the temperature will increase because of the elevation loss,” Clark said. “For every 1,000 meters of elevation loss, it warms about six degrees (Celsius). That elevation loss would accelerate the melting of the Greenland ice sheet.”

In contrast, the Antarctic ice sheet is so cold that elevation loss won’t affect it the same way. The melting of the ice sheet there comes primarily from the calving of icebergs, which float away and melt in warmer ocean waters, or the contact between the edges of the ice sheet and seawater.

In their paper, the authors note that sea-level rise in the past century has been dominated by the expansion of the ocean and melting of glaciers. The biggest contributions in the future may come from melting of the Greenland ice sheet, which could disappear entirely, and the Antarctic ice sheet, which will likely reach some kind of equilibrium with atmospheric temperatures and shrink significantly, but not disappear.

“Keep in mind that the sea level rise projected by these models of 2.3 meters per degree of warming is over thousands of years,” emphasized Clark, who is a professor in Oregon State University’s College of Earth, Ocean, and Atmospheric Sciences. “If it warms a degree in the next two years, sea levels won’t necessarily rise immediately. The Earth has to warm and hold that increased temperature over time.

“However, carbon dioxide has a very long time scale and the amounts we’ve emitted into the atmosphere will stay up there for thousands of years,” he added. “Even if we were to reduce emissions, the sea-level commitment of global warming will be significant.”

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Peter Clark, cell phone: 541-740-5237 (clarkp@geo.oregonstate.edu)

Researchers document acceleration of ocean denitrification during deglaciation

CORVALLIS, Ore. – As ice sheets melted during the deglaciation of the last ice age and global oceans warmed, oceanic oxygen levels decreased and “denitrification” accelerated by 30 to 120 percent, a new international study shows, creating oxygen-poor marine regions and throwing the oceanic nitrogen cycle off balance.

By the end of the deglaciation, however, the oceans had adjusted to their new warmer state and the nitrogen cycle had stabilized – though it took several millennia. Recent increases in global warming, thought to be caused by human activities, are raising concerns that denitrification may adversely affect marine environments over the next few hundred years, with potentially significant effects on ocean food webs.

Results of the study have been published this week in the journal Nature Geoscience. It was supported by the National Science Foundation.

“The warming that occurred during deglaciation some 20,000 to 10,000 years ago led to a reduction of oxygen gas dissolved in sea water and more denitrification, or removal of nitrogen nutrients from the ocean,” explained Andreas Schmittner, an Oregon State University oceanographer and author on the Nature Geoscience paper. “Since nitrogen nutrients are needed by algae to grow, this affects phytoplankton growth and productivity, and may also affect atmospheric carbon dioxide concentrations.”

“This study shows just what happened in the past, and suggests that decreases in oceanic oxygen that will likely take place under future global warming scenarios could mean more denitrification and fewer nutrients available for phytoplankton,” Schmittner added.

In their study, the scientists analyzed more than 2,300 seafloor core samples, and created 76 time series of nitrogen isotopes in those sediments spanning the past 30,000 years. They discovered that during the last glacial maximum, the Earth’s nitrogen cycle was at a near steady state. In other words, the amount of nitrogen nutrients added to the oceans – known as nitrogen fixation – was sufficient to compensate for the amount lost by denitrification.

A lack of nitrogen can essentially starve a marine ecosystem by not providing enough nutrients. Conversely, too much nitrogen can create an excess of plant growth that eventually decays and uses up the oxygen dissolved in sea water, suffocating fish and other marine organisms.

Following the period of enhanced denitrification and nitrogen loss during deglaciation, the world’s oceans slowly moved back toward a state of near stabilization. But there are signs that recent rates of global warming may be pushing the nitrogen cycle out of balance.

“Measurements show that oxygen is already decreasing in the ocean,” Schmittner said “The changes we saw during deglaciation of the last ice age happened over thousands of years. But current warming trends are happening at a much faster rate than in the past, which almost certainly will cause oceanic changes to occur more rapidly.

“It still may take decades, even centuries to unfold,” he added.

Schmittner and Christopher Somes, a former graduate student in the OSU College of Earth, Ocean, and Atmospheric Sciences, developed a model of nitrogen isotope cycling in the ocean, and compared that with the nitrogen measurements from the seafloor sediments. Their sensitivity experiments with the model helped to interpret the complex patterns seen in the observations.

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Andreas Schmittner, 541-737-9952; aschmittner@coas.oregonstate.edu

OSU geographer to receive international prize for mediation

CORVALLIS, Ore. – An Oregon State University faculty member has won a major international prize for his mediation efforts in water conflicts.

Aaron Wolf, a geography professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences, has been named a 2013 recipient of Il Monito del Giardino (The Warning from the Garden) Award by the Bardini and Peyron Monumental Parks Foundation of Florence, Italy.

The honor is given to persons who have distinguished themselves internationally in safeguarding the environment and raising awareness of ecological issues. The 2012 recipient was Jane Goodall.

Wolf will receive his award next week June in Florence.

The scientific committee cited Wolf’s involvement in striving for more democratic access to the world’s water sources. “The value of his work has come to be recognized on the world stage, mediation work in controversies relative to water’s being at the center of the geopolitical scences that are very delicate, such as that of the Mideast.”

Wolf has traveled throughout the world as both a scientist and a mediator in the area of water conflicts. He has been a consultant to the U.S. Department of State, the U.S. Agency for International Development, the World Bank, and numerous governments.

He directs the Program in Water Conflict Management and Transformation, and developed the Transboundary Freshwater Dispute database, which includes a compilation of 400 water-related treaties as well as information on water conflicts and resolution.

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Aaron Wolf, 541-737-2722; wolf@geo.oregonstate.edu

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Natural Resources Leadership Academy 2012
Aaron Wolf

Occasional raindrops do little to address drying state

CORVALLIS, Ore. – When Oregonians can rototill their gardens in March, but then have to water their lawns all throughout April and May, you know it’s drier than usual.

Experts say that through May 10, it has been the driest start to the year on record at the Eugene and Salem airport weather stations, and the second driest start at Hyslop Farm in Corvallis and the Medford Airport. This is the third driest start to the year for the Portland Airport station.

“We’ve seen some pretty drastic swings from very wet to very dry over the past year,” said Oregon State University’s Kathie Dello, who is the deputy director of the Oregon Climate Service at OSU. “The whole West Coast has been abnormally dry. We’ve had some strong high pressure ridging, which means the storm track is sent to our north.

“When it does that, we get weather that generally results in hot days and cool nights,” Dello said, “and it is usually quite dry.”

The spring of 2012 – from March to May – was the fourth wettest on record statewide, and then things dried up quickly. The summer July to September period was the second driest on record. But the fall October to December period saw above-normal precipitation, before the transition to this spring’s dry conditions.

“It’s been pretty topsy-turvy,” Dello said. “On one hand, we built up a nice snowpack through November and December in the central and northern Cascades, but abnormally warm temperatures are melting that quickly.”

More than 91 percent of Oregon is considered abnormally dry for this time of year, Dello said, citing the U.S. Drought Monitor. The NOAA Climate Prediction Center shows that the odds favor the dry trend continuing into July.

“The biggest concern when that happens is warm, dry ground and early melting of snow,” Dello said. “That equates to fire danger. The National Interagency Fire Center is saying that fire season may begin weeks earlier than normal this year.

“And, of course, dry conditions are a concern for farmers, stream health and fish,” she added. “We have seen occasional bouts of cloudiness and sprinkles, but not enough to chase the overall pattern of dryness.”

For the record:

  • Through May 10, the Eugene Airport has received just 6.54 inches of rain, which is 14.08 inches below normal. It is the driest on record dating back to 1940.
  • The Salem Airport has had 7.65 inches of rain, driest on record back to 1928, and 9.67 inches below normal.
  • The Corvallis Hyslop station has received 8.27 inches of rain, second driest on record back to 1893 and 10.59 inches below normal. The driest on record was in 2001, when it got just 7.98 inches.
  • Medford Airport has received a scant 3.05 inches, which is 4.48 inches below normal in records dating back to 1928. The driest start to a year on record was in 1992 with 2.99 inches.
  • Portland Airport has logged 8.3 inches of precipitation, 6.55 inches before normal and third driest since 1942. The record year was in 1985, with 6.0 inches.

Weather-lovers can learn more about Oregon weather by following Dello on Twitter at: www.twitter.com/orclimatesvc. The state is also looking for volunteers to collect precipitation data. For more information, go to http://www.cocorahs.org/.

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Kathie Dello, 541-737-8927

Study traces origin of cirrus clouds primarily to mineral dust and metals

CORVALLIS, Ore. – Researchers studying the origin of cirrus clouds have found that these thin, wispy trails of ice crystals are formed primarily on dust particles and some unusual combinations of metal particles – both of which may be influenced by human activities.

The findings are important, scientists say, because cirrus clouds cover as much as one-third of the Earth and play an important role in global climate. Depending on altitude and the number and size of ice crystals, cirrus clouds can cool the planet by reflecting incoming solar radiation – or warm it by trapping outgoing heat.

However, what the net effect is, and how humans impact it, is still unclear.

Results of the study, which was funded by NASA and the National Science Foundation, were published this week in the journal Science.

“Cirrus clouds are complicated but the important message is that dust and certain metals provide the seeds for a majority of the ice crystals that form the clouds,” said Cynthia Twohy, an Oregon State University atmospheric scientist and co-author on the study. “Other particle types – including bacteria and soot from human-produced combustion or natural sources – don’t seem to contribute much to the nuclei of cirrus crystals.

“These biological particles may be important in the formation of lower altitude clouds,” added Twohy, who is a professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “But they were surprisingly absent from the particles we sampled from cirrus clouds.”

During the study, led by scientists at the Massachusetts Institute of Technology and the National Oceanic and Atmospheric Administration, the researchers conducted flight missions from 2002 to 2011 over North America and Central America at 20,000 to 50,000 feet elevation, where cirrus clouds often form. As their planes flew through the clouds, researchers captured and heated the ice crystals, which then evaporated, leaving behind a tiny kernel that they analyzed using an onboard mass spectrometer.

Despite the length of the study and its different geographic locations, the researchers found similar outcomes: About 60 percent of the cloud particles they analyzed could be traced to mineral dust blown into the atmosphere, or to metallic aerosols.

“Mineral dust can occur naturally,” Twohy said, “or it can be influenced by human activities. Certainly the major deserts like the Sahara and Gobi are enormous sources of mineral dust. But agriculture, over-grazing and climate and land-use changes can also contribute.”

Twohy said the scientists have not yet traced the origin of the dust to see how much of it came from natural versus anthropogenic causes. The metallic aerosols, she added, are unusual and may be easier to trace to specific sources. Containing elements like lead, zinc, tin and copper, they appear to be from industrial activities, according to other scientists in the study.

“As the climate warms, it is possible that we will see an expansion of desert lands, which could lead to even more dust entering the atmosphere,” Twohy said. “That could create more cirrus clouds, but what that means in terms of warming or cooling is unsure and an area for future research.”

An expert in cloud formation, Twohy has been involved in some 30 different aircraft missions over the years to understand the composition and characteristics of clouds and how they are influenced by pollution. She has studied clouds in North America, Central America, South America, Africa, the Southern Ocean and the Indian Ocean.

“At lower altitudes, clouds are known to be influenced by pollution – especially near cities,” Twohy said. “They have more droplets, they reflect more light and they rain less. The impacts of cirrus clouds on climate are much more complex. But this gives us a starting point because we now have a better understanding of the particle types and mechanisms that lead to their formation.”

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Cynthia Twohy, 541-737-5690

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College of Earth, Ocean, and Atmospheric Sciences

About the OSU College of Earth, Ocean, and Atmospheric Sciences: CEOAS is internationally recognized for its faculty, research and facilities, including state-of-the-art computing infrastructure to support real-time ocean/atmosphere observation and prediction. The college is a leader in the study of the Earth as an integrated system, providing scientific understanding to address complex environmental challenges