Climate & Climate Change

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  

Investing in climate observations would generate major returns

November 14, 2017 | A major new paper by more than two dozen climate experts concludes that a well-designed climate observing system could deliver trillions of dollars in benefits while providing decision makers with the information they need in coming decades to protect public health and the economy."We are on the threshold of a new era in prediction, drawing on our knowledge of the entire Earth system to strengthen societal resilience to potential climate and weather disasters," said Antonio Busalacchi, president of the University Corporation for Atmospheric Research and one of the co-authors. "Strategic investments in observing technologies will pay for themselves many times over by protecting life and property, promoting economic growth, and providing needed intelligence to decision makers."Elizabeth Weatherhead, a scientist with the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder, is the lead author of the new paper, published last week in Earth's Future. The co-authors include two scientists associated with the National Center for Atmospheric Research: Jeffrey Lazo and Kevin Trenberth.The scientists urge that investments focus on tackling seven grand challenges. These include predicting extreme weather and climate shifts, the role of clouds and circulation in regulating climate, regional sea level change and coastal impacts, understanding the consequences of melting ice, and feedback loops involving carbon cycling.For more about the paper, see the CIRES news release.

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

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

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

Quantifying the benefits of cutting carbon

September 18, 2017 | Perhaps tens of thousands of studies have detailed the possible impacts of a changing climate: the amount of sea level rise we can expect by the end of the century, for example, or the regions of the world that will likely experience more severe droughts.But rarely do these studies outline the actual benefits that society would gain from emitting fewer greenhouse gases instead of more. Instead, they often compare what is likely to happen in a particular scenario — such as emissions continuing unabated — to what the climate was like in the past."Most studies don't give us a good sense of what we have to gain by mitigating. What are the benefits of capping warming at 2 degrees Celsius instead of 3, for example?" said NCAR scientist Brian O'Neill. "That's important information for policy makers because mitigation has a price, and you need to understand the benefits to weigh them against the cost."O'Neill and dozens of colleagues from NCAR and universities across the country have recently wrapped up a major effort to wrestle with this problem. The results from the project — the Benefits of Reduced Anthropogenic Climate changE (BRACE) — are published in a special issue of the journal Climatic Change.For BRACE, scientists explored what the world would look like through 2100 in two different scenarios: a business-as-usual emissions scenario with a temperature increase of about 3.7 degrees Celsius over preindustrial levels and a moderate mitigation scenario where warming is reduced to about 2.5 degrees Celsius. By comparing the two worlds, they were able to calculate the benefits of moderate mitigation for a range of areas, from agriculture to health to extreme events.Additionally, the researchers looked at how different pathways of societal development — including population growth, economic growth, and technological development — might play a role or even outweigh the climate effects."It's important to analyze the effects of societal change alongside the effects of climate change," O'Neill said. "Societal change can matter as much as climate change. And in some cases, it matters more."The results of the studies vary significantly across sectors. When it comes to extreme heat, for example, the benefits of reducing emissions are clear and significant. In other areas, the findings are more nuanced. In agriculture, for example, the potential fertilizing effects of higher levels of carbon dioxide in the atmosphere and the ability of some farmers to adapt — by adding nitrogen fertilizer in regions where it isn't currently used, for example — could in some cases mute, or even cancel out, the benefits of mitigation.The BRACE project has studied the benefits of reducing greenhouse gas emissions in a number of areas, including extreme heat, mosquito-borne diseases, droughts, tropical cyclones, and agriculture. (Photo collage, UCAR.)Natural variability or climate change?For the studies, the scientists relied on two sets of simulations from the NCAR-based Community Earth System Model. For each set — one representing a future with no mitigation and the other a future with moderate mitigation — the scientists drew from more than a dozen simulations. Having an "ensemble" of model runs allowed them to better estimate extreme events, which occur rarely by definition and are therefore difficult to capture with just one or two simulations. It also allowed them to distinguish the effects of human-caused climate change from natural climate variability.In many cases, the ensembles allowed the scientists to demonstrate a substantial benefit of mitigating greenhouse gas emissions. One study found that extreme heat waves that today have just a one in 20 chance of occurring in any given year could become six to 20 times more common if greenhouse gas emissions continue unabated. In the moderate mitigation scenario, such heat waves would likely become just 2 to 4 times more common.Other studies of extreme heat showed similar benefits. For example, scientists found the likelihood that a single summer between 2060 and 2080 would be hotter than any in the historical record to be 80 percent if greenhouse gas emissions continue unabated. But that risk is cut in half, to 41 percent, with moderate mitigation.In some areas of study, however, natural variability still overwhelms the impact of climate change, making it difficult to measure the benefits of mitigation. This was true for several BRACE studies that looked at how tropical cyclones — and the damage they can cause — would differ between the two scenarios. The studies found that tropical cyclone damage (and number of storms) might actually increase if greenhouse gas emissions are reduced, though the intensity of storms might also be lessened.However, the storm findings were not statistically robust, meaning the data were too noisy to detect a clear signal."Tropical cyclones are highly variable, so to show a real difference between the present and the future, we would need to run the model many more times to accurately describe how present and future storms are different," said NCAR scientist Andrew Gettelman, who led one of the studies.Still, there are several plausible explanations for why hurricane activity might decrease if greenhouse gas emissions continue on their current trajectory. For example, uneven warming of the ocean basins could generate high-level winds, which make it more difficult for storms to form.However, storms might still be more intense due to increases in ocean temperature, and indeed Gettelman and colleagues found increases in frequency for the most intense landfalling storms, despite decreases in overall storm numbers.The BRACE researchers' work on this topic is made more difficult by the relatively short historical record that exists for hurricanes. Though observations of landfalling hurricanes stretch back as long as people have lived near coasts, a comprehensive record of how many cyclones form across the globe's oceans only began at the dawn of the satellite era in 1979. With only a few decades of data to create a baseline, it's difficult to detect future trends, Gettelman said.Additionally, global climate models are typically run at a resolution that is too coarse for individual cyclones to form. While hurricanes do form in climate models when run at a high resolution, it is not yet clear that those storms are behaving in a way that matches what would happen in the real world.The societal effect Even if climate models could accurately simulate tropical cyclones, it might still be difficult to determine the benefit, at least in terms of decreased damage, that might be realized if greenhouse gas emissions were cut. That's because societal choices also play an important role. For example, in the study led by Gettelman, the researchers found that any potential changes in storms and the damage they cause were swamped by the projected increase in societal vulnerability: more people and more buildings are projected to be near coastlines, in harm's way.This societal effect also dominated the climate effect in other areas studied for the BRACE project, including heat-related mortality in Houston, and total population exposure to the Aedes aegypti mosquito, which carries diseases including Zika, dengue, and chikungunya."When it comes to human health outcomes, climate change usually becomes an exacerbating factor," said NCAR scientist Andrew Monaghan, who led the study on Aedes aegypti. "Other important factors are governance decisions, socioeconomic development, and population growth trajectories."Monaghan and colleagues found that the amount of land that is climatically suitable for the mosquito to live would increase by 13 percent without any mitigation of greenhouse gases, compared to 8 percent in a moderate mitigation scenario. But the number of people who would be exposed to the mosquito would increase by as much as 130 percent as the population grows in regions where the mosquito can thrive.The societal effect may also be dominant in certain aspects of agriculture, according to the BRACE studies. Fertilizing or irrigating additional land could increase crop yields, for example. And crops that are particularly vulnerable to climate change could be replaced with hardier varieties.Agricultural uncertaintyThe BRACE studies that tried to quantify the agricultural benefits of mitigation also had to contend with another area of uncertainty: How much of a fertilizing effect will increased carbon dioxide in the atmosphere have on crop yield? Plants need carbon dioxide to grow, and greater availability of carbon dioxide can bolster crop yields. But there are other limiting factors at play, including available water, soil nutrients, and extreme heat.One BRACE study that included the fertilizing effects of increased carbon dioxide found that crop yields would grow by a global average of 11 percent if greenhouse gas emissions continue on their current trajectory. By comparison, the global average would increase just 6 percent with moderate mitigation."We've already observed a massive ramp-up in crop yields from the 1960s through the current day, due to changes in fertilizer, crop varieties, management, and carbon dioxide levels," said NCAR scientist Peter Lawrence, who worked on the agricultural aspects of the BRACE project. "The big question is what happens as we move forward. We know that our models can accurately represent the relationship between increased carbon dioxide and increased plant growth. But there are a lot of processes our models don't capture, including flooding and the effects of heat waves while plants are flowering."Other agricultural studies in the BRACE project that looked at specific crops found net positive benefits from reducing greenhouse gases. For example, one study found that climate change would decrease potential maize yields in the future (relative to what they would be in the absence of climate change). Maize yields would decrease by a global mean of 27 percent if emissions continue unabated vs. 15 percent with moderate mitigation. Another study found that the exposure of crops to damaging heat above a critical threshold for growth would be reduced by about a third in the moderate mitigation scenario compared to the scenario with no mitigation.The agricultural studies highlight the stubborn uncertainties that persist when trying to determine how crops will be affected in a warming world. And while this makes quantifying the benefits of mitigation more difficult, it also helps set the direction for future research.O'Neill says he hopes all of the more than 20 studies published so far in the BRACE framework will inform the direction of future work, including what questions need to be asked and what kinds of model simulations would prove most useful for finding answers."Even though the BRACE project involved dozens of scientists to research a broad range of sectors, it is really just a start," said O'Neill.About the articleTitle: The Benefits of Reduced Anthropogenic Cliamte changE (BRACE): a synthesisAuthors: Brian C. O’Neill1, James M. Done, Andrew Gettelman, Peter Lawrence, Flavio Lehner, Jean-Francois Lamarque, Lei Lin, Andrew J. Monaghan, Keith Oleson, Xiaolin Ren, Benjamin M. Sanderson, Claudia Tebaldi, Matthias Weitzel, Yangyang Xu, Brooke Anderson, Miranda J. Fix, and Samuel LevisJournal: Climatic Change DOI: 10.1007/s10584-017-2009-xCollaboratorsArgonne National LaboratoryBrigham Young UniversityCity University of New YorkColorado School of MinesColorado State UniversityJohns HopkinsIndian Space Research Organization, IndiaLanzhou University, ChinaLawrence Berkeley National LaboratoryNational Oceanic and Atmospheric AdministrationStanford UniversityStony Brook UniversitySun Yat-sen University, ChinaSwiss Federal Institute of TechnologyTexas A&MThe Climate CorporationUniversity of ArizonaUniversity of Colorado BoulderUniversity of Illinois UrbanaUniversity of WashingtonWriter/contact:Laura Snider, Senior Science Writer and Public Information Officer 

Dino-killing asteroid could have thrust Earth into two years of darkness

BOULDER, Colo. — Tremendous amounts of soot, lofted into the air from global wildfires following a massive asteroid strike 66 million years ago, would have plunged Earth into darkness for nearly two years, new research finds. This would have shut down photosynthesis, drastically cooled the planet, and contributed to the mass extinction that marked the end of the age of dinosaurs.These new details about how the climate could have dramatically changed following the impact of a 10-kilometer-wide asteroid will be published Aug. 21 in the Proceedings of the National Academy of Sciences. The study, led by the National Center for Atmospheric Research (NCAR) with support from NASA and the University of Colorado Boulder, used a world-class computer model to paint a rich picture of how Earth’s conditions might have looked at the end of the Cretaceous Period, information that paleobiologists may be able to use to better understand why some species died, especially in the oceans, while others survived.Scientists estimate that more than three-quarters of all species on Earth, including all non-avian dinosaurs, disappeared at the boundary of the Cretaceous-Paleogene periods, an event known as the K-Pg extinction. Evidence shows that the extinction occurred at the same time that a large asteroid hit Earth in what is now the Yucatán Peninsula. The collision would have triggered earthquakes, tsunamis, and even volcanic eruptions.Scientists also calculate that the force of the impact would have launched vaporized rock high above Earth's surface, where it would have condensed into small particles known as spherules. As the spherules fell back to Earth, they would have been heated by friction to temperatures high enough to spark global fires and broil Earth's surface. A thin layer of spherules can be found worldwide in the geologic record."The extinction of many of the large animals on land could have been caused by the immediate aftermath of the impact, but animals that lived in the oceans or those that could burrow underground or slip underwater temporarily could have survived," said NCAR scientist Charles Bardeen, who led the study. "Our study picks up the story after the initial effects — after the earthquakes and the tsunamis and the broiling. We wanted to look at the long-term consequences of the amount of soot we think was created and what those consequences might have meant for the animals that were left."Other study co-authors are Rolando Garcia and Andrew Conley, both NCAR scientists, and Owen “Brian” Toon, a researcher at the University of Colorado Boulder.An illustration of an asteroid impacting Earth. (Image courtesy NASA.)A world without photosynthesisIn past studies, researchers have estimated the amount of soot that might have been produced by global wildfires by measuring soot deposits still preserved in the geologic record. For the new study, Bardeen and his colleagues used the NCAR-based Community Earth System Model (CESM) to simulate the effect of the soot on global climate going forward. They used the most recent estimates of the amount of fine soot found in the layer of rock left after the impact (15,000 million tons), as well as larger and smaller amounts, to quantify the climate's sensitivity to more or less extensive fires.In the simulations, soot heated by the Sun was lofted higher and higher into the atmosphere, eventually forming a global barrier that blocked the vast majority of sunlight from reaching Earth's surface. “At first it would have been about as dark as a moonlit night," Toon said.While the skies would have gradually brightened, photosynthesis would have been impossible for more than a year and a half, according to the simulations. Because many of the plants on land would have already been incinerated in the fires, the darkness would likely have had its greatest impact on phytoplankton, which underpin the ocean food chain. The loss of these tiny organisms would have had a ripple effect through the ocean, eventually devastating many species of marine life.The research team also found that photosynthesis would have been temporarily blocked even at much lower levels of soot. For example, in a simulation using only 5,000 million tons of soot — about a third of the best estimate from measurements — photosynthesis would still have been impossible for an entire year.In the simulations, the loss of sunlight caused a steep decline in average temperatures at Earth's surface, with a drop of 50 degrees Fahrenheit (28 degrees Celsius) over land and 20 degrees Fahrenheit (11 degrees Celsius) over the oceans.While Earth's surface cooled in the study scenarios, the atmosphere higher up in the stratosphere actually became much warmer as the soot absorbed light from the Sun. The warmer temperatures caused ozone destruction and allowed for large quantities of water vapor to be stored in the upper atmosphere. The water vapor then chemically reacted in the stratosphere to produce hydrogen compounds that led to further ozone destruction. The resulting ozone loss would have allowed damaging doses of ultraviolet light to reach Earth's surface after the soot cleared.The large reservoir of water in the upper atmosphere formed in the simulations also caused the layer of sunlight-blocking soot to be removed abruptly after lingering for years, a finding that surprised the research team. As the soot began to settle out of the stratosphere, the air began to cool. This cooling, in turn, caused water vapor to condense into ice particles, which washed even more soot out of the atmosphere. As a result of this feedback loop — cooling causing precipitation that caused more cooling — the thinning soot layer disappeared in just a few months.Challenging the modelWhile the scientists think the new study gives a robust picture of how large injections of soot into the atmosphere can affect the climate, they also caution that the study has limitations.For example, the simulations were run in a model of modern-day Earth, not a model representing what Earth looked like during the Cretaceous Period, when the continents were in slightly different locations. The atmosphere 66 million years ago also contained somewhat different concentrations of gases, including higher levels of carbon dioxide.Additionally, the simulations did not try to account for volcanic eruptions or sulfur released from the Earth's crust at the site of the asteroid impact, which would have resulted in an increase in light-reflecting sulfate aerosols in the atmosphere.The study also challenged the limits of the computer model's atmospheric component, known as the Whole Atmosphere Community Climate Model (WACCM)."An asteroid collision is a very large perturbation — not something you would normally see when modeling future climate scenarios," Bardeen said. "So the model was not designed to handle this and, as we went along, we had to adjust the model so it could handle some of the event's impacts, such as warming of the stratosphere by over 200 degrees Celsius."These improvements to WACCM could be useful for other types of studies, including modeling a "nuclear winter" scenario. Like global wildfires millions of years ago, the explosion of nuclear weapons could also inject large amounts of soot into the atmosphere, which could lead to a temporary global cooling."The amount of soot created by nuclear warfare would be much less than we saw during the K-Pg extinction," Bardeen said. "But the soot would still alter the climate in similar ways, cooling the surface and heating the upper atmosphere, with potentially devastating effects."Writer:Laura Snider, Senior Science Writer

UCAR statement on U.S. withdrawal from Paris climate agreement

BOULDER, Colo. — President Donald Trump today announced he is withdrawing the United States from the Paris Agreement on climate change, a global pact signed by more than 190 countries to cut carbon dioxide emissions. He also said he would seek to renegotiate it or forge a new agreement. Antonio J. Busalacchi, the president of the University Corporation for Atmospheric Research (UCAR), issued the following statement:Today's decision to begin withdrawing from the Paris Agreement under its current terms creates new uncertainties about the future of our climate. At a time when our economic well-being and national security depend increasingly on accurate predictions of the impacts of greenhouse gas emissions, investments in climate research are even more necessary so scientists can project climate change in the new policy environment.Climate change poses major risks to food and water supplies, transportation systems, and other resources in the United States and worldwide. Rising temperatures and their impacts on weather patterns are creating additional stress at a time of international conflicts, endangering our economic and military security. If average global temperatures rise more than 2 degrees Celsius — the target of the Paris Agreement — research indicates that damaging impacts, such as sea level rise, intense heat waves and droughts, and shifts in weather patterns and storms will become more severe. With today’s decision, scientists will need to focus more attention on the potential ramifications of failing to curb emissions sufficiently to meet the 2-degree target.Nations are amassing information about future climate conditions as a necessary precondition for competing in the global marketplace. Multinational corporations are seeking to mitigate their exposure to climate risks, and if they cannot get the needed information from U.S.-funded research they will go elsewhere to get the most authoritative information. U.S. rivals, including China, are conducting vigorous climate research projects that support their economic and military investments and expand their influence worldwide. Even if the United States no longer participates in climate agreements, it cannot afford to cede climate knowledge to overseas competitors.Climate research is fundamentally nonpartisan. The work under way at the National Center for Atmospheric Research, in collaboration with our partners at government agencies, the university community, and the private sector, builds an evidence-based picture of the possible future impacts of climate change. As always, we stand ready to provide the results of our scientific inquiry to Congress and the administration in order to keep our nation secure and prosperous.Today's decision does not mean that climate change will go away. To the contrary, the heightened potential for increased greenhouse gas emissions poses a substantial threat to our communities, businesses, and military. The work by U.S. researchers — to understand and anticipate changes in our climate system and determine ways to mitigate or adapt to the potential impacts — is now more vital than ever.

Decades of data on world's oceans reveal a troubling oxygen decline

NCAR scientist Matthew Long is a co-author of a new study appearing in Geophysical Research Letters. This is an excerpt from a news release by Georgia Tech, a UCAR member institution. May 11, 2017 | A new analysis of decades of data on oceans across the globe has revealed that the amount of dissolved oxygen contained in the water – an important measure of ocean health – has been declining for more than 20 years.Researchers at Georgia Institute of Technology looked at a historic dataset of ocean information stretching back more than 50 years and searched for long term trends and patterns. They found that oxygen levels started dropping in the 1980s as ocean temperatures began to climb.“The oxygen in oceans has dynamic properties, and its concentration can change with natural climate variability,” said Taka Ito, an associate professor in Georgia Tech’s School of Earth and Atmospheric Sciences who led the research. “The important aspect of our result is that the rate of global oxygen loss appears to be exceeding the level of nature's random variability.”The study, which was published April in Geophysical Research Letters, was sponsored by the National Science Foundation and the National Oceanic and Atmospheric Administration. The team included researchers from the National Center for Atmospheric Research, the University of Washington-Seattle, and Hokkaido University in Japan.Read the full news release from Georgia Tech.Global map of the linear trend of dissolved oxygen at the depth of 100 meters. (Image courtesy Georgia Tech.) About the articleTitle: Upper ocean O2 trends: 1958–2015Authors: Takamitsu Ito, Shoshiro Minobe, Matthew C. Long, and Curtis DeutschJournal: Geophysical Research Letters, DOI: 10.1002/2017GL073613

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