NCAR

North American storm clusters could produce 80 percent more rain

BOULDER, Colo. — Major clusters of summertime thunderstorms in North America will grow larger, more intense, and more frequent later this century in a changing climate, unleashing far more rain and posing a greater threat of flooding across wide areas, new research concludes.The study, by scientists at the National Center for Atmospheric Research (NCAR), builds on previous work showing that storms are becoming more intense as the atmosphere is warming. In addition to higher rainfall rates, the new research finds that the volume of rainfall from damaging storms known as mesoscale convective systems (MCSs) will increase by as much as 80 percent across the continent by the end of this century, deluging entire metropolitan areas or sizable portions of states."The combination of more intense rainfall and the spreading of heavy rainfall over larger areas means that we will face a higher flood risk than previously predicted," said NCAR scientist Andreas Prein, the study's lead author. "If a whole catchment area gets hammered by high rain rates, that creates a much more serious situation than a thunderstorm dropping intense rain over parts of the catchment.""This implies that the flood guidelines which are used in planning and building infrastructure are probably too conservative," he added.The research team drew on extensive computer modeling that realistically simulates MCSs and thunderstorms across North America to examine what will happen if emissions of greenhouse gases continue unabated.The study will be published Nov. 20 in the journal Nature Climate Change. It was funded by the National Science Foundation, which is NCAR's sponsor, and by the U.S. Army Corps of Engineers. Hourly rain rate averages for the 40 most extreme summertime mesoscale convective systems (MCSs) in the current (left) and future climate of the mid-Atlantic region. New research shows that MSCs will generate substantially higher maximum rain rates over larger areas by the end of the century if society continues a "business as usual" approach of emitting greenhouse gases . (©UCAR, Image by Andreas Prein, NCAR. This image is freely available for media & nonprofit use.)A warning signalThunderstorms and other heavy rainfall events are estimated to cause more than $20 billion of economic losses annually in the United States, the study notes. Particularly damaging, and often deadly, are MSCs: clusters of thunderstorms that can extend for many dozens of miles and last for hours, producing flash floods, debris flows, landslides, high winds, and/or hail. The persistent storms over Houston in the wake of Hurricane Harvey were an example of an unusually powerful and long-lived MCS.Storms have become more intense in recent decades, and a number of scientific studies have shown that this trend is likely to continue as temperatures continue to warm. The reason, in large part, is that the atmosphere can hold more water as it gets warmer, thereby generating heavier rain.A study by Prein and co-authors last year used high-resolution computer simulations of current and future weather, finding that the number of summertime storms that produce extreme downpours could increase by five times across parts of the United States by the end of the century. In the new study, Prein and his co-authors focused on MCSs, which are responsible for much of the major summertime flooding east of the Continental Divide. They investigated not only how their rainfall intensity will change in future climates, but also how their size, movement, and rainfall volume may evolve.Analyzing the same dataset of computer simulations and applying a special storm-tracking algorithm, they found that the number of severe MCSs in North America more than tripled by the end of the century. Moreover, maximum rainfall rates became 15 to 40 percent heavier, and intense rainfall reached farther from the storm's center. As a result, severe MCSs increased throughout North America, particularly in the northeastern and mid-Atlantic states, as well as parts of Canada, where they are currently uncommon.The research team also looked at the potential effect of particularly powerful MCSs on the densely populated Eastern Seaboard. They found, for example, that at the end of the century, intense MCSs over an area the size of New York City could drop 60 percent more rain than a severe present-day system. That amount is equivalent to adding six times the annual discharge of the Hudson River on top of a current extreme MCS in that area."This is a warning signal that says the floods of the future are likely to be much greater than what our current infrastructure is designed for," Prein said. "If you have a slow-moving storm system that aligns over a densely populated area, the result can be devastating, as could be seen in the impact of Hurricane Harvey on Houston."This satellite image loop shows an MCS developing over West Virginia on June 23, 2016. The resulting floods caused widespread flooding, killing more than 20 people.  MCSs are responsible for much of the major flooding east of the Continental Divide during warm weather months. (Image by NOAA National Weather Service, Aviation Weather Center.) Intensive modelingAdvances in computer modeling and more powerful supercomputing facilities are enabling climate scientists to begin examining the potential influence of a changing climate on convective storms such as thunderstorms, building on previous studies that looked more generally at regional precipitation trends.For the new study, Prein and his co-authors turned to a dataset created by running the NCAR-based Weather and Research Forecasting (WRF) model over North America at a resolution of 4 kilometers (about 2.5 miles). That is sufficiently fine-scale resolution to simulate MCSs. The intensive modeling, by NCAR scientists and study co-authors Roy Rasmussen, Changhai Liu, and Kyoko Ikeda, required a year to run on the Yellowstone system at the NCAR-Wyoming Supercomputing Center.The team used an algorithm developed at NCAR to identify and track simulated MCSs. They compared simulations of the storms at the beginning of the century, from 2000 to 2013, with observations of actual MCSs during the same period and showed that the modeled storms are statistically identical to real MCSs.The scientists then used the dataset and algorithm to examine how MCSs may change by the end of the century in a climate that is approximately 5 degrees Celsius (9 degrees Fahrenheit) warmer than in the pre-industrial era — the temperature increase expected if greenhouse gas emissions continue unabated.About the paperTitle: Increased rainfall volume from future convective storms in the USAuthors: Andreas F Prein, Changhai Liu, Kyoko Ikeda, Stanley B Trier, Roy M Rasmussen, Greg J Holland, Martyn P ClarkJournal: Nature Climate Change  

New research could predict La Niña drought years in advance

NCAR Senior Scientist Clara Deser is a co-author of two new studies, published this month in the journal Geophysical Resarch Letters, that examine the impacts and predictability of La Niña. The following excerpt is from a news release by the University of Texas at Austin, a UCAR Member.Nov. 16, 2017 | Two new studies from The University of Texas at Austin have significantly improved scientists’ ability to predict the strength and duration of droughts caused by La Niña – a recurrent cooling pattern in the tropical Pacific Ocean. Their findings, which predict that the current La Niña is likely to stretch into a second year, could help scientists know years in advance how a particular La Niña event is expected to evolve.“Some La Niña events last two years, and predicting them is extremely challenging,” said Pedro DiNezio, a research associate at the University of Texas Institute for Geophysics (UTIG).The studies were published in November in the journal Geophysical Research Letters. DiNezio and UTIG Research Associate Yuko Okumura were authors on both studies and collaborated with scientists from the National Center for Atmospheric Research (NCAR). UTIG is a research unit of the UT Jackson School of Geosciences.The southern United States, including parts of eastern Texas, regularly experiences warm and dry winters caused by La Niña. Therefore, predicting La Niña’s evolution, particularly its duration, is key. Read the full news release.

UCAR Congressional Briefing: Moving research to industry

WASHINGTON — Federally funded scientific advances are enabling the multibillion-dollar weather industry to deliver increasingly targeted forecasts to consumers and businesses, strengthening the economy and providing the nation with greater resilience to natural disasters, experts said today at a congressional briefing.The panel of experts, representing universities, federally funded labs, and the private sector, said continued government investment in advanced computer modeling, observing tools, and other basic research provides the foundation for improved forecasts.The nonprofit University Corporation for Atmospheric Research (UCAR) sponsored the briefing."Thanks to a quiet revolution in modern weather prediction, we can all use forecasts to make decisions in ways that wouldn't have been possible just 10 years ago," said Rebecca Morss, a senior scientist with the National Center for Atmospheric Research (NCAR) and deputy director of the center's Mesoscale and Microscale Meteorology Lab. "Now we are looking to the next revolution, which includes giving people longer lead times and communicating risk as effectively as possible."Fuqing Zhang, a professor of meteorology and statistics at Pennsylvania State University, highlighted the ways that scientists are advancing their understanding of hurricanes and other storms with increasingly detailed observations and computer modeling. Researchers at Penn State, for example, fed data from the new National Oceanic and Atmospheric Administration GOES-R satellite into NOAA's powerful FV3 model to generate an experimental forecast of Hurricane Harvey that simulated its track and intensity."The future of weather forecasting is very promising," said Zhang, who is also the director of the Penn State Center for Advanced Data Assimilation and Predictability Techniques.  "With strategic investments in observations, modeling, data assimilation, and supercomputing, we will see some remarkable achievements."Mary Glackin, director of science and forecast operations for The Weather Company, an IBM business, said the goal of the weather industry is to help consumers and businesses make better decisions, both by providing its own forecasts and by forwarding alerts from the National Weather Service. The Weather Company currently is adapting a powerful research weather model based at NCAR, the Model for Prediction Across Scales (MPAS), for use in worldwide, real-time forecasts.The NCAR-based Model for Prediction Across Scales simulates the entire globe while enabling scientists to zoom in on areas of interest. It is one of the key tools for improving forecasts in the future. (©UCAR. This image is freely available for media & nonprofit use.) "We have a weather and climate enterprise that we can be extremely proud of as a nation, but it's not where it should be," Glackin said. "Weather affects every consumer and business, and the public-private partnership can play a pivotal role in providing better weather information that is critically needed."Antonio Busalacchi, president of UCAR, emphasized the benefits of partnerships across the academic, public, and private sectors. He said that research investments by the National Science Foundation, NOAA, and other federal agencies are critical for improving forecasts that will better protect vulnerable communities and strengthen the economy."These essential collaborations between government agencies, universities, and private companies are driving landmark advances in weather forecasting," Busalacchi said. "The investments that taxpayers are making in basic research are paying off many times over by keeping our nation safer and more prosperous."The briefing was the latest in a series of UCAR Congressional Briefings that draw on expertise from UCAR's university consortium and public-private partnerships to provide insights into critical topics in the Earth system sciences. Past briefings have focused on wildfires, predicting space weather, aviation weather safety, the state of the Arctic, hurricane prediction, potential impacts of El Niño, and new advances in water forecasting.

New climate forecasts for watersheds - and the water sector

Nov. 10, 2017 | Water managers and streamflow forecasters can now access bi-weekly, monthly, and seasonal precipitation and temperature forecasts that are broken down by individual watersheds, thanks to a research partnership between the National Center for Atmospheric Research (NCAR) and the University of Colorado Boulder (CU Boulder). The project is sponsored by the National Oceanic and Atmospheric Administration (NOAA) through the Modeling, Applications, Predictions, and Projections program.Operational climate forecasts for subseasonal to seasonal time scales are currently provided by the NOAA Climate Prediction Center and other sources. The forecasts usually take the form of national contour maps (example) and gridded datasets at a relatively coarse geographic resolution. Some forecast products are broken down further, based on state boundaries or on climate divisions, which average two per state; others are summarized for major cities. But river forecasters and water managers grapple with climate variability and trends in the particular watersheds within their service areas, which do not align directly with the boundaries of existing forecast areas. A forecast that directly describes predicted conditions inside an individual watershed would be extremely valuable to these users for making decisions in their management areas, such as how much water to release or store in critical reservoirs and when.To bridge this gap, the NCAR–CU Boulder research team has developed a new prototype prediction system that maps climate forecasts to watershed boundaries over the contiguous United States in real time. The system is currently running at NCAR, with real-time forecasts and analyses available on a demonstration website."We are trying to improve the accessibility and relevance of climate predictions for streamflow forecasting groups and water managers," said NCAR scientist Andy Wood, who co-leads the project. "We can’t solve all the scientific challenges of climate prediction, but we can make it easier for a person thinking about climate and water in a river basin — such as the Gunnison, or the Yakima, or the Potomac — to find and download operational climate information that has been tailored to that basin’s observed variability."The project is funded by NOAA, and the scientists plan to hand off successful components of the system for experimental operational evaluation within the NOAA National Weather Service.  Collaborators include scientists from the NOAA Climate Prediction Center and partners from the major federal water agencies: the U.S. Army Corps of Engineers and the Bureau of Reclamation.This screenshot of the S2S Climate Outlooks for Watersheds website shows forecasted temperature anomalies for watersheds across the contiguous United States. As users scroll across different watersheds, they get more precise information. In this screenshot from early November 2017, the forecast is showing that, over the next one to two weeks, the Colorado Headwaters watershed is expected to be 1.2 degrees warmer than normal. Visit the website to learn more. (©UCAR. This image is freely available for media & nonprofit use.)  Beyond the standard weather forecastPrecipitation and temperature forecasts that extend beyond the typical 7- to 10-day window can be useful to water managers making a number of important decisions about how to best regulate supplies. For instance, during a wet water year, when snowpack is high and reservoirs are more full than usual, the relative warmth or coolness of the coming spring can affect how quickly the snow melts. Good spring season forecasts allow water managers to plan in advance for how to best manage the resulting runoff.For water systems in drought, such as California's during 2012–2015, early outlooks on whether the winter rainy season will help alleviate the drought or exacerbate it can help water utilities strategize ways of meeting the year’s water demands. Historically, making these kinds of longer-term predictions accurately has been highly challenging. But in recent years, scientists have improved their skill at subseasonal and seasonal climate prediction. NOAA’s National Centers for Environmental Prediction plays a key role, both running an in-house modeling system — the Climate Forecast System, version 2 (CFSv2) — and leading an effort called the North American Multi-Model Ensemble (NMME). These model-based forecasts help inform the NOAA official climate forecasts, which also include other tools and expert judgment. NMME combines forecasts from seven different climate models based in the U.S. and Canada to form a super-ensemble of climate predictions that extend up to 10 months into the future. The combination of the different forecasts is often more accurate than the forecast from any single model. Temperature forecasts, in particular, from the combined system are notably more accurate than they were 10 years ago, Wood said, partly due to their representation of observed warming trends. Even with these new tools, however, predicting seasonal precipitation beyond the first month continues to be a major challenge. The NCAR–CU Boulder project makes use of both the CFSv2 and NMME forecasts. It generates predictions for bi-weekly periods (weeks 1-2, 2-3, and 3-4) from CFSv2 that are updated daily and longer-term forecasts derived from the NMME (months 1, 2, 3, and season 1) that are updated monthly. The scientists currently map these forecasts to 202 major watersheds in the contiguous U.S.Analyzing forecast skillThe resulting watershed-specific forecasts are available in real-time on the project's interactive website, which also provides information about their accuracy and reliability."It's important for users to be able to check on the quality of the forecasts," said Sarah Baker, a doctoral student in the Civil, Environmental, and Architectural Engineering Department at CU Boulder. "We're able to use hindcasts, which are long records of past forecasts, to analyze and describe the skill of the current forecasts. Baker, who also works for the Bureau of Reclamation, has been building the prototype system under the supervision of Wood and her academic adviser, CU Professor Balaji Rajagopalan. The researchers are also using analyses of forecast accuracy and reliability to begin correcting for systematic biases — such as consistently over-predicting springtime rains in one watershed or under-predicting summertime heat in another — in the forecasts.The project team has presented the project at a number of water-oriented meetings in the western U.S. Water managers, operators, and researchers from agencies such as the Bureau of Reclamation and utilities such as the Southern Nevada Water Authority, which manages water for Las Vegas, have expressed interest in the new forecast products."This project has great potential to provide climate outlook information that is more relevant for hydrologists and the water sector. It will be critical to connect with stakeholders or possible users of the forecasts so that their needs can continue to help shape this type of information product," said NOAA’s Andrea Ray. Ray leads an effort funded by NIDIS, the National Integrated Drought Information System, to identify tools and information such as this for a NOAA online Water Resources Monitor and Outlook that would also help connect stakeholders to climate and water information.In the coming year, the research team will implement statistical post-processing methods to improve the accuracy of the forecasts. They will also investigate the prediction of extreme climate events at the watershed scale. ContactAndy Wood, NCAR Research Applications LaboratoryWebsitehttp://hydro.rap.ucar.edu/s2sCollaboratorsCU BoulderNCARNOAAU.S. Army Corps of EngineersBureau of Reclamation FunderNOAA's Modeling, Applications, Predictions and Projections Climate Testbed program

AGU, AMS honor NCAR scientists

BOULDER, Colo. — Three senior scientists from the National Center for Atmospheric Research (NCAR) have been recognized by professional organizations for their exceptional contributions in the atmospheric and climate sciences. NCAR Distinguished Senior Scientist Kevin Trenberth is being awarded the Roger Revelle Medal by the American Geophysical Union (AGU). The honor, named after a renowned oceanographer, is given annually to recognize “outstanding contributions in atmospheric sciences, atmosphere-ocean coupling, atmosphere-land coupling, biogeochemical cycles, climate or related aspects of the Earth system.”Trenberth is an expert in climate variability and climate change, and he has pioneered research into the interactions between the atmosphere and the oceans, especially the El Niño and La Niño cycle. Trenberth will receive the medal at the AGU annual meeting in December, held this year in New Orleans.NCAR Senior Scientist Clara Deser has been chosen by the American Meteorological Society (AMS) to be the 2018 Walter Orr Roberts Lecturer at the organization's annual meeting, to be held in January in Austin, Texas. The appointment, named after NCAR's founding director, is conferred in "recognition of significant contributions to the understanding of atmospheric processes derived from multidisciplinary research activities."Deser's lecture, which will be given Jan. 11, is  "New Perspectives on the Role of Internal Variability in Regional Climate Change and Climate Model Evaluation." She uses both models and observations to study climate variability and climate change.NCAR Senior Scientist Gordon Bonan has been named a fellow of the AMS. Fellows are elected for making "outstanding contributions to the atmospheric or related oceanic or hydrologic sciences or their applications during a substantial period of years."Bonan's research examines the interactions of terrestrial ecosystems with climate. He specializes in the development of, and experimentation with, models of the Earth's biosphere, atmosphere, hydrosphere, and geosphere systems.Kevin TrenberthClara DeserGordon Bonan

New approach to geoengineering simulations is significant step forward

BOULDER, Colo. — Using a sophisticated computer model, scientists have demonstrated for the first time that a new research approach to geoengineering could potentially be used to limit Earth’s warming to a specific target while reducing some of the risks and concerns identified in past studies, including uneven cooling of the globe.The scientists developed a specialized algorithm for an Earth system model that varies the amount and location of geoengineering — in this case, injections of sulfur dioxide high into the atmosphere — that would in theory be needed, year to year, to effectively cap warming. They caution, however, that more research is needed to determine if this approach would be practical, or even possible, in the real world.The findings from the new research, led by scientists from the National Center for Atmospheric Research (NCAR), Pacific Northwest National Laboratory (PNNL), and Cornell University, represent a significant step forward in the field of geoengineering. Still, there are many questions that need to be answered about sulfur dioxide injections, including how this type of engineering might alter regional precipitation patterns and the extent to which such injections would damage the ozone layer. The possibility of a global geoengineering effort to combat warming also raises serious governance and ethical concerns."This is a major milestone and offers promise of what might be possible in the future,” said NCAR scientist Yaga Richter, one of the lead authors. “But it is just the beginning; there is a lot more research that needs to be done."Past modeling studies have typically sought to answer the question "What happens if we do geoengineering?" The results of those studies have described the outcomes — both positive and negative — of injecting a predetermined amount of sulfates into the atmosphere, often right at Earth's equator. But they did not attempt to specify the outcome they hoped to achieve at the outset.In a series of new studies, the researchers turned the question around, instead asking, "How might geoengineering be used to meet specific climate objectives?""We have really shifted the question, and by doing so, found that we can better understand what geoengineering may be able to achieve," Richter said.The research findings are detailed in a series of papers published in a special issue of the Journal of Geophysical Research – Atmospheres.Mimicking a volcanoIn theory, geoengineering — large-scale interventions designed to modify the climate — could take many forms, from launching orbiting solar mirrors to fertilizing carbon-hungry ocean algae. For this research, the team studied one much-discussed approach: injecting sulfur dioxide into the upper atmosphere, above the cloud layer.The idea of combating global warming with these injections is inspired by history's most massive volcanic eruptions. When volcanoes erupt, they loft sulfur dioxide high into the atmosphere, where it's chemically converted into light-scattering sulfate particles called aerosols. These sulfates, which can linger in the atmosphere for a few years, are spread around the Earth by stratospheric winds, forming a reflective layer that cools the planet.To mimic these effects, sulfur dioxide could be injected directly into the stratosphere, perhaps with the help of high-flying aircraft. But while the injections would counter global warming, they would not address all the problems associated with climate change, and they would likely have their own negative side effects.For example, the injections would not offset ocean acidification, which is linked directly to carbon dioxide emissions. Geoengineering also could result in significant disruptions in rainfall patterns as well as delays in healing the ozone hole. Moreover, once geoengineering began, if society wanted to avoid a rapid and drastic increase in temperature, the injections would need to continue until mitigation efforts were sufficient to cap warming on their own.There would also likely be significant international governance challenges that would have to be overcome before a geoengineering program could be implemented."For decision makers to accurately weigh the pros and cons of geoengineering against those of human-caused climate change, they need more information," said PNNL scientist Ben Kravitz, also a lead author of the studies. "Our goal is to better understand what geoengineering can do — and what it cannot."Modeling the complex chemistryFor the new studies, the scientists used the NCAR-based Community Earth System Model with its extended atmospheric component, the Whole Atmosphere Community Climate Model. WACCM includes detailed chemistry and physics of the upper atmosphere and was recently updated to simulate stratospheric aerosol evolution from source gases, including geoengineering."It was critical for this study that our model be able to accurately capture the chemistry in the atmosphere so we could understand how quickly sulfur dioxide would be converted into aerosols and how long those aerosols would stick around," said NCAR scientist Michael Mills, also a lead author. "Most global climate models do not include this interactive atmospheric chemistry.”The scientists also significantly improved how the model simulates tropical stratospheric winds, which change direction every few years. Accurately representing these winds is critical to understanding how aerosols are blown around the planet.The scientists successfully tested their model by seeing how well it could simulate the massive 1991 eruption of Mount Pinatubo, including the amount and rate of aerosol formation, as well as how those aerosols were transported around the globe and how long they stayed in the atmosphere.Then the scientists began to explore the impacts of injecting sulfur dioxide at different latitudes and altitudes. From past studies, the scientists knew that sulfates injected only at the equator affect Earth unevenly: over-cooling the tropics and under-cooling the poles. This is especially problematic since climate change is warming the Arctic at a faster rate. Climate change is also causing the Northern Hemisphere to warm more quickly than the Southern Hemisphere.The researchers used the model to study 14 possible injection sites at seven different latitudes and two different altitudes — something never before tried in geoengineering research. They found that they could spread the cooling more evenly across the globe by choosing injection sites on either side of the equator.The simulations on the left represent how global temperatures are expected to change if greenhouse gas emissions continue on a "business as usual" trajectory. The simulations on the right show how temperature could be stabilized in a model by injecting sulfur dioxide high into the atmosphere at four separate locations. Because greenhouse gases are being emitted at the same rate in the simulations on the left and the right, stopping geoengineering would result in a drastic spike in global temperatures. (©UCAR. This image is freely available for media & nonprofit use.)  Meeting multiple objectivesThe researchers then pieced together all their work into a single model simulation with specific objectives: to limit average global warming to 2020 levels through the end of the century and to minimize the difference in cooling between the equator and the poles as well as between the northern and southern hemispheres.They gave the model four choices of injection sites — at 15 degrees and 30 degrees North and South in latitude — and then implemented an algorithm that determines, for each year, the best injection sites and the quantity of sulfur dioxide needed at those sites. The model's ability to reformulate the amount of geoengineering needed each year, based on that year's conditions, also allowed the simulation to respond to natural fluctuations in the climate.The model successfully kept the surface temperatures near 2020 levels against a background of increasing greenhouse gas emissions that would be consistent with a business-as-usual scenario. The algorithm’s ability to choose injection sites cooled the Earth more evenly than in previous studies, because it could inject more sulfur dioxide in regions that were warming too quickly and less in areas that had over-cooled.However, by the end of the century, the amount of sulfur dioxide that would need to be injected each year to offset human-caused global warming would be enormous: almost five times the amount spewed into the air by Mount Pinatubo on June 15, 1991.Flipping the research question"The results demonstrate that it is possible to flip the research question that's been guiding geoengineering studies and not just explore what geoengineering does but see it as a design problem,” said Doug MacMartin, a scientist at Cornell and the California Institute of Technology. “When we see it in that light, we can then start to develop a strategy for how to meet society’s objectives."In the current series of studies, adjusting the geoengineering plan just once a year allowed the researchers to keep the average global temperature to 2020 levels in a given year, but regional temperatures — as well as seasonal temperature changes — were sometimes cooler or hotter than desired. So next steps could include exploring the possibility of making more frequent adjustments at a different choice of injection locations.The scientists are already working on a new study to help them understand the possible impacts geoengineering might have on regional phenomena, such as the Asian monsoons."We are still a long way from understanding all the interactions in the climate system that could be triggered by geoengineering, which means we don’t yet understand the full range of possible side effects," said NCAR scientist Simone Tilmes, a lead author. "But climate change also poses risks. Continuing research into geoengineering is critical to assess benefits and side effects and to inform decision makers and society."The research was funded by the Defense Advanced Research Projects Agency and the National Science Foundation, NCAR's sponsor.Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or the Defense Advanced Research Projects Agency.About the papers:Titles:Radiative and chemical response to interactive stratospheric sulfate aerosols in fully coupled CESM1(WACCM), DOI: 10.1002/2017JD027006Sensitivity of aerosol distribution and climate response to stratospheric SO2 injection locations, DOI: 10.1002/2017JD026888Stratospheric Dynamical Response and Ozone Feedbacks in the Presence of SO2 Injections, DOI: 10.1002/2017JD026912The climate response to stratospheric aerosol geoengineering can be tailored using multiple injection locations, DOI: 10.1002/2017JD026868First simulations of designing stratospheric sulfate aerosol geoengineering to meet multiple simultaneous climate objectives, DOI: 10.1002/2017JD026874Authors: B. Kravitz, D. MacMartin, M. J. Mills, J. H. Richter, and S. TilmesCo-authors: F. Vitt, J. J. Tribbia, J.-F. LamarqueJournal: Journal of Geophysical Research – AtmospheresData access: All the data from the experiments are available on the Earth System Gridathttps://www.earthsystemgrid.org/dataset/ucar.cgd.ccsm4.so2_geoeng.htmlorhttp://dx.doi.org/10.5065/D6X63KMM and https://www.earthsystemgrid.org/dataset/ucar.cgd.ccsm4.so2_ctl_fb.html orhttp://dx.doi.org/10.5065/D6PC313T.Writer:Laura Snider, Senior Science Writer

Future volcanic eruptions could cause more climate disruption

BOULDER, Colo. — Major volcanic eruptions in the future have the potential to affect global temperatures and precipitation more dramatically than in the past because of climate change, according to a new study led by the National Center for Atmospheric Research (NCAR). The study authors focused on the cataclysmic eruption of Indonesia's Mount Tambora in April 1815, which is thought to have triggered the so-called "year without a summer" in 1816. They found that if a similar eruption occurred in the year 2085, temperatures would plunge more deeply, although not enough to offset the future warming associated with climate change. The increased cooling after a future eruption would also disrupt the water cycle more severely, decreasing the amount of precipitation that falls globally. The reason for the difference in climate response between 1815 and 2085 is tied to the oceans, which are expected to become more stratified as the planet warms, and therefore less able to moderate the climate impacts caused by volcanic eruptions. "We discovered that the oceans play a very large role in moderating, while also lengthening, the surface cooling induced by the 1815 eruption," said NCAR scientist John Fasullo, lead author of the new study. "The volcanic kick is just that — it's a cooling kick that lasts for a year or so. But the oceans change the timescale. They act to not only dampen the initial cooling but also to spread it out over several years." The research was published today in the journal Nature Communications. The work was funded in part by the National Science Foundation, NCAR's sponsor. Other funders include NASA and the U.S. Department of Energy. The study co-authors are Robert Tomas, Samantha Stevenson, Bette Otto-Bliesner, and Esther Brady, all of NCAR, as well as Eugene Wahl, of the National Oceanic and Atmospheric Administration.An aerial view of Mount Tambora's caldera, formed during the 1815 eruption. (Image credit: Wikipedia.) A detailed look at a deadly pastMount Tambora's eruption, the largest in the past several centuries, spewed a huge amount of sulfur dioxide into the upper atmosphere, where it turned into sulfate particles called aerosols. The layer of light-reflecting aerosols cooled Earth, setting in motion a chain of reactions that led to an extremely cold summer in 1816, especially across Europe and the northeast of North America. The "year without a summer" is blamed for widespread crop failure and disease, causing more than 100,000 deaths globally. To better understand and quantify the climate effects of Mount Tambora's eruption and to explore how those effects might differ for a future eruption if climate change continues on its current trajectory, the research team turned to a sophisticated computer model developed by scientists from NCAR and the broader community. The scientists looked at two sets of simulations from the Community Earth System Model. The first was taken from the CESM Last Millennium Ensemble Project, which simulates Earth's climate from the year 850 through 2005, including volcanic eruptions in the historic record. The second set, which assumes that greenhouse gas emission continue unabated, was created by running CESM forward and repeating a hypothetical Mount Tambora eruption in 2085. The historical model simulations revealed that two countervailing processes helped regulate Earth's temperature after Tambora's eruption. As aerosols in the stratosphere began blocking some of the Sun's heat, this cooling was intensified by an increase in the amount of land covered by snow and ice, which reflected heat back to space. At the same time, the oceans served as an important counterbalance. As the surface of the oceans cooled, the colder water sank, allowing warmer water to rise and release more heat into the atmosphere. By the time the oceans themselves had cooled substantially, the aerosol layer had begun to dissipate, allowing more of the Sun's heat to again reach Earth's surface. At that point, the ocean took on the opposite role, keeping the atmosphere cooler, since the oceans take much longer to warm back up than land. "In our model runs, we found that Earth actually reached its minimum temperature the following year, when the aerosols were almost gone," Fasullo said. "It turns out the aerosols did not need to stick around for an entire year to still have a year without a summer in 1816, since by then the oceans had cooled substantially."The oceans in a changed climateWhen the scientists studied how the climate in 2085 would respond to a hypothetical eruption that mimicked Mount Tambora's, they found that Earth would experience a similar increase in land area covered by snow and ice. However, the ocean's ability to moderate the cooling would be diminished substantially in 2085. As a result, the magnitude of Earth's surface cooling could be as much as 40 percent greater in the future. The scientists caution, however, that the exact magnitude is difficult to quantify since they had only a relatively small number of simulations of the future eruption. The reason for the change has to do with a more stratified ocean. As the climate warms, sea surface temperatures increase. The warmer water at the ocean's surface is then less able to mix with the colder, denser water below. In the model runs, this increase in ocean stratification meant that the water that was cooled after the volcanic eruption became trapped at the surface instead of mixing deeper into the ocean, reducing the heat released into the atmosphere. The scientists also found that the future eruption would have a larger effect on rainfall than the historical eruption of Mount Tambora. Cooler sea surface temperatures decrease the amount of water that evaporates into the atmosphere and, therefore, also decrease global average precipitation. Though the study found that Earth's response to a Tambora-like eruption would be more acute in the future than in the past, the scientists note that the average surface cooling caused by the 2085 eruption (about 1.1 degrees Celsius) would not be nearly enough to offset the warming caused by human-induced climate change (about 4.2 degrees Celsius by 2085). Study co-author Otto-Bliesner said, "The response of the climate system to the 1815 eruption of Indonesia's Mount Tambora gives us a perspective on potential surprises for the future, but with the twist that our climate system may respond much differently."About the article:Title: The amplifying influence of increased ocean stratification on a future year without a summer Authors: J.T. Fasullo, R. Tomas, S. Stevenson, B. Otto-Bliesner, E. Brady, and E. Wahl Journal: Nature Communications, DOI: 10.1038/s41467-017-01302-z

Scientists pinpoint sources of Front Range ozone

BOULDER, Colo. — A comprehensive new air quality report for the state of Colorado quantifies the sources of summertime ozone in Denver and the northern Front Range, revealing the extent to which motor vehicles and oil and gas operations are the two largest local contributors to the pollutant.The new report, based on intensive measurements taken from aircraft and ground sites as well as sophisticated computer simulations, also concludes that unhealthy levels of ozone frequently waft up to remote mountain areas, including Rocky Mountain National Park.Scientists at the National Center for Atmospheric Research (NCAR) wrote the report with support from colleagues at NASA, drawing on a pair of 2014 field campaigns that tracked both local and distant contributors to pollution on the northern Front Range. The research was funded by the Colorado Department of Public Health and Environment (CDPHE), NASA, and the National Science Foundation, which is NCAR's sponsor."We found that, on high ozone days, a critical portion of the ozone pollution here on the Front Range is the result of local activities, especially traffic and oil and gas operations," said NCAR scientist Gabriele Pfister, an author of the new report. "The pollution doesn't just affect the metro area. Prevailing daytime winds often transport the ozone to the west, exposing the foothills and mountains to high ozone levels."Scientists involved in the 2014 field campaigns have published some of the findings in peer-reviewed scientific journals.The report is designed to provide information to the CDPHE, which is working to reduce unhealthy levels of ozone in the Northern Colorado Front Range Metropolitan Area that stretches from Denver's southern suburbs to Fort Collins.“The NCAR analysis provides important information that helps inform our ongoing efforts to better understand ozone formation and craft cost-effective strategies to reduce ozone levels and protect public health,” said Larry Wolk, executive director and chief medical officer at the Colorado Department of Public Health and Environment.This visulization of surface ozone across the Front Range on an August afternoon shows how ozone pollution can sometimes be more accute in the high mountains than on the populated plains, depending on local winds. (©UCAR. This image is freely available for media & nonprofit use.)Tracing an invisible gasAn invisible but harmful pollutant, ground-level ozone can lead to increased asthma attacks and other respiratory ailments, producing symptoms that include coughing, trouble breathing, and chest pain. It also can be damaging to vegetation, including crops.Ozone can be challenging to trace because it is the product of other pollutants. It forms in the atmosphere from chemical reactions of hydrocarbons and carbon monoxide in the presence of nitrogen oxides and sunlight. It peaks during the summer, when sunshine is most abundant.Denver has a background ozone level of about 40-50 parts per billion (ppb) that is generated by numerous sources outside of the region. With the additional ozone generated by local emissions, the area on summer days often exceeds the federal health standard, which is set at an average of 70 ppb over an eight-hour period.The report finds that cars, trucks, and other motor vehicles are the primary local contributors to ozone in the heavily developed urban corridor that stretches from Denver's southern suburbs to about the city of Boulder. Further north, however, emissions from oil and gas operations are the primary local contributors to ozone between Boulder and Fort Collins. Motor vehicles and oil and gas operations each contribute, on average, 30-40 percent to total local ozone production in the region on days when ozone exceeds the health standard, the report states.Depending on prevailing winds, the air masses from the southern and northern parts of the metro area sometimes mix, enabling emissions from a variety of sources to produce ozone more readily. These sources include power plants, industrial facilities, and Denver International Airport.The scientists warned of the potential for more ozone pollution to accompany expected population increases."The Denver metropolitan area will keep growing," said NCAR scientist Frank Flocke, a co-author of the report. "Total miles driven will keep increasing."However, computer simulations run by the research team indicated that lowering local emissions could result in substantial ozone reductions. In some scenarios, ozone could be reduced by 6-10 ppb, which could make the difference between meeting or exceeding the national ambient air quality standards for ozone.Leveraging two research projectsThe report was commissioned as part of a major field project in the summer of 2014 led by Pfister and Flocke. The Front Range Air Pollution and Photochemistry Experiment (FRAPPÉ) relied on specially equipped aircraft, mobile radars, balloon-mounted sensors, and advanced computer models to measure emissions from industrial facilities, power plants, motor vehicles, agricultural operations, oil and gas drilling, fires, and other human-related and natural sources.The FRAPPÉ team coordinated with a NASA-led air quality mission that took place on the Front Range at the same time: DISCOVER-AQ (Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality).Colorado, like other states, relies on a limited number of ground-based stations to monitor air quality and help guide statewide policies and permitting. The field projects provided a much more detailed and complete, three-dimensional picture of the processes that affect air quality, including conditions far upwind and high up in the atmosphere.The new report recommends additional monitoring of pollutants that lead to ozone formation at key ground sites. It also recommends comprehensive aircraft studies in the future to monitor air quality along the Front Range as the population increases and emissions sources change.The report, "Process-Based and Regional Source Impact Analysis for FRAPPÉ and DISCOVER-AQ 2014," was submitted to the CDPHE in July and published online earlier this month.

Climate change could decrease Sun's ability to disinfect lakes, coastal waters

October 20, 2017 | One of the largely unanticipated impacts of a changing climate may be a decline in sunlight's ability to disinfect lakes, rivers, and coastal waters, possibly leading to an increase in waterborne pathogens and the diseases they can cause in humans and wildlife.A new study published in the journal Scientific Reports outlines how a rise in the amount of organic matter washed into bodies of water can stunt the ability of pathogen-killing ultraviolet rays from the Sun to penetrate the water's surface.Scientists have already measured an increase in "browning" of the world's waters, a phenomenon caused by more organic matter washing in from the surrounding land. This trend is expected to continue as a warming climate leads to more extreme rainfall and thawing permafrost, both of which contribute to the problem.In the new study, led by Miami University in Ohio, researchers analyzed water samples and used a model based at the National Center for Atmospheric Research (NCAR) to quantify, for the first time, the impact of dissolved organic matter on the potential for UV radiation from the Sun to kill pathogens in the water."Much of the research emphasis up to this point has been on the browning itself, not the ecological consequences," said lead author Craig Williamson, an ecologist at Miami University. "We were able to determine that in some cases, browning is decreasing the ability of sunlight to disinfect water by a factor of 10. This could have serious implications for drinking water supplies and coastal fisheries across the globe."The study was an outgrowth of collaboration among multiple scientists from different disciplines who serve on the United Nations Environment Programme Environmental Effects Assessment Panel (UNEP EEAP). The data collection and modeling used in this study were funded by multiple grants from the National Science Foundation, NCAR's sponsor.Quantifying the impactsFor the study, Williamson and his colleagues relied on water samples collected from lakes around the world, from Pennsylvania and Wisconsin to Chile and New Zealand. The water samples were tested to determine how much dissolved organic matter each contained, as well as the wavelengths of light — including ultraviolet wavelengths — absorbed by that organic matter.The pristine waters of Lake Tahoe's Sand Harbor contrast with the brown water in the lake's Star Harbor, where people and boats are active. Dissolved organic matter from human activity and from heavy rains can cloud the water and reduce solar disinfection. (Photo courtesy Andrew Tucker.)Then NCAR scientist Sasha Madronich used this information as well as modeling results from the Tropospheric Ultraviolet-Visible model to calculate the solar inactivation potential (SIP) for each lake. SIP is an index of the expected disinfecting power of UV light in a particular body of water, based on its dissolved organic matter and other characteristics.The NCAR Tropospheric Ultraviolet-Visible model — which simulates how UV light is scattered and absorbed as it passes through Earth's atmosphere — was used to determine how much UV light hits the surface of the lakes throughout the year.Madronich also analyzed reflection and refraction off each lake's surface to calculate how much light penetrates the lakes and then, finally, how deeply it reaches.Because scientists already have some understanding of which wavelengths of UV light do the most damage to which waterborne pathogens, the scientists were able to use the model output to calculate the SIP for each lake. In some cases, they also calculated this measure of expected disinfecting power across different parts of, or for different time periods in, the same lake.The results allowed scientists to quantify the impacts of dissolved organic matter. For example, the summertime SIP for one lake in northeastern Pennsylvania — which, along with other regional lakes has undergone significant browning in recent decades — dropped by about half between 1994 and 2015.In California's Lake Tahoe, the SIP can be as much as ten times lower at Tahoe Meeks Bay, an area at lake's edge that is heavily used by humans and has a much higher level of dissolved organic matter, than in the relatively pristine center of the lake.The scientists also showed how SIP can dramatically decrease after a heavy rainfall event, using water samples collected from the region where the Manitowoc River flows into Lake Michigan, which supplies drinking water to more than 10 million people. Modeling based on samples taken before and after a strong storm moved through on June 21, 2011, showed that the SIP may have dropped by as much as 22 percent due to the extra dissolved organic matter that washed into the area in this single storm event.Additionally, the results for all lakes showed a significantly stronger SIP during the summer — when the Sun is higher in the sky — than winter. Lakes at higher elevations also had higher SIPs during all times of the year.Collaborating across disciplinesThe study highlights possible challenges for water supply managers and public health workers as the climate continues to warm and extreme precipitation events become more common. Not only does an increase in dissolved organic matter make it more difficult for sunlight to disinfect bodies of water, it also makes it more difficult for water treatment plants to work effectively, Williamson said. In the United States, 12 to 19 million people already become ill from waterborne pathogens annually.The research also underscores the importance of working across scientific disciplines to fully understand the impacts of climate change across the Earth system, said Madronich, who is an atmospheric chemist."What happens in the atmosphere affects what happens in lakes," he said. "These are not separate compartments of the world. These things are all connected."Other co-authors of the study are Aparna Lal and Robyn Lucas (The Australian National University), Richard Zepp (Environmental Protection Agency), Erin Overholt (Miami University), Kevin Rose (Rensselaer Polytechnic Institute), Geoffrey Schladow (University of California, Davis), and Julia Lee-Taylor (NCAR).About the articleTitle: Climate change-induced increases in precipitation are reducing the potential for solar ultraviolet radiation to inactivate pathogens in surface watersAuthors: Craig E. Williamson, Sasha Madronich, Aparna Lal, Richard G. Zepp, Robyn M. Lucas, Erin P. Overholt, Kevin C. Rose, S. Geofrey Schladow, and Julia Lee-TaylorJournal: Scientific Reports, DOI: 10.1038/s41598-017-13392-2Writer/contact:Laura Snider, Senior Science Writer

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