NCAR

Pioneering NCAR Photochemist Passes

June 29, 2016 | Jack Calvert, a preeminent researcher in photochemistry, atmospheric chemistry, and air pollution, died on June 1 at the age of 93 in Tennessee.

Calvert joined NCAR as a senior scientist in 1981, after serving for more than three decades as a professor of chemistry at Ohio State University. His chosen specialty was the investigation of chemical reactions initiated by light.

While at NCAR, Calvert led the Atmospheric Kinetics and Photochemistry Group until he retired in 1993 and was appointed emeritus senior scientist.

Pioneering HAO research recognized by National Academy of Sciences

June 28, 2016 | Former HAO Senior Scientist Tim Brown has received a prestigious award from the National Academy of Sciences for landmark research that he conducted while at NCAR in the 1990s and early 2000s.

The James Craig Watson Medal is presented every two years for outstanding contributions to the science of astronomy. It recognizes Brown for pioneering instrument developments and observations, and for formulating a method to make extremely sensitive images of the Sun, which became key to the field of helioseismology.

Capping warming at 2 degrees

June 27, 2016 | Even if countries adhere to the Paris climate agreement hammered out last fall, capping global warming at 2 degrees Celsius would likely require net zero greenhouse gas emissions by 2085 and substantial negative emissions over the long term, according to an in-depth analysis by scientists at the National Center for Atmospheric Research (NCAR). More than 100 parties to the Paris Agreement submitted pledges to the United Nations Framework Convention on Climate Change outlining their individual commitments to cutting greenhouse gas emissions by 2025 or 2030.  The new study finds that, even if all the countries follow through on their commitments, steeper cuts would be necessary after 2030 to stay below 2 degrees of warming. And by the end of the century, total emissions would need to become negative, meaning more greenhouse gases would be removed from the air than are emitted into the atmosphere. These negative emissions would need to reach net minus 15 gigatons of "carbon dioxide equivalent," a measure that tabulates the global warming potential of all types of greenhouse gases in relation to carbon dioxide, according to model simulations created for the study. Worldwide, yearly greenhouse gas emissions now equal about 50 gigatons of carbon dioxide equivalent. "The emissions targets in the Paris Agreement are an important first step, and it's known that additional action will be required to meet the goal of limiting warming to 2 degrees," said NCAR scientist Benjamin Sanderson, lead author of the study. "This paper provides details of what the next steps would need to look like in order to actually hit that target." The study, published in Geophysical Research Letters, a journal of the American Geophysical Union, was funded by the U.S. Department of Energy and by the National Science Foundation, NCAR's sponsor.   This graph represents eight possible pathways that society could take to have a two-in-three chance of limiting warming to 2 degrees Celsius.  The blue line represents our current emissions trajectory. The red line represents the path that society will be on if countries adhere to the Paris Agreement. The gray lines represent other possibilities, all of which require more stringent emissions cuts in the near term but fewer negative emissions later. Click to enlarge. (©UCAR. This image is freely available for media & nonprofit use.) Small changes now equal big benefits later Even before the Paris agreement was finished, it was clear that the pledged emissions cuts by 2030 would not be sufficient on their own to meet the target of limiting warming to 2 degrees. This study gives a comprehensive look at the possible paths society could take to have a two-in-three chance of staying below the target. "We created a wide range of possible global emissions pathways that would allow us to have a decent shot at limiting warming to two degrees," said Sanderson. "We found that very small increases in the rate at which we cut greenhouse gases now could lead to very large decreases in the amount of negative emissions we need later."  Negative emissions in the future will require the massive deployment of technologies that are still hypothetical to draw down greenhouse gases from the atmosphere. That makes it difficult to know how capable society will be to implement large-scale carbon removal in the future. Sanderson and his colleagues, NCAR scientists Brian O'Neill and Claudia Tebaldi, also found that it is still possible to stay below 2 degrees of warming without net negative emissions, but to do so would require near-term cuts that are much more aggressive than those proposed in the Paris agreement. About the article Benjamin M. Sanderson, Brian C. O’Neill, and Claudia Tebaldi, What would it take to achieve the Paris temperature targets?, Geophysical Research Letters Writer/contact:Laura Snider, Senior Science Writer

Climate modeling 101: Explanations without equations

A new book breaks down climate models into easy-to-understand concepts. (Photo courtesy Springer.) June 21, 2016 | Climate scientists tell us it's going to get hotter. How much it rains and where it rains is likely to shift. Sea level rise is apt to accelerate. Oceans are on their way to becoming more acidic and less oxygenated. Floods, droughts, storms, and other extreme weather events are projected to change in frequency or intensity.  But how do they know what they know? For climate scientists, numerical models are the tools of the trade. But for the layperson — and even for scientists in other fields — climate models can seem mysterious. What does "numerical" even mean? Do climate models take other things besides the atmosphere into account?How do scientists know if a model is any good? * Two experts in climate modeling, Andrew Gettelman of the National Center for Atmospheric Research and Richard Rood of the University of Michigan, have your answers and more, free of charge. In a new open-access book, "Demystifying Climate Models," the pair lay out the fundamentals. In 282 pages, the scientists explain the basics of climate science, how that science is translated into a climate model, and what those models can tell us (as well as what they can't) — all without using a single equation. *Find the answers on pages 8, 13, and 161, respectively, of the book. AtmosNews sat down with Gettelman to learn more about the book, which anyone can download at http://www.demystifyingclimate.org.   NCAR scientist Andrew Gettelman has written a new book on climate modeling with Richard Rood of the University of Michigan. (Courtesy photo. This image is freely available for media & nonprofit use.) What was the motivation to write this book? There isn't really another book that sets out the philosophy and structure of models. There are textbooks, but inside you'll find a lot of physics and chemistry: information about momentum equations, turbulent fluxes — which is useful if you want to build your own model. And then there are books on climate change for the layperson, and they devote maybe a paragraph to climate modeling. There's not much in the middle. This book provides an introduction for the beginning grad student, or someone in another field who is interested in using model output, or anyone who is just curious how climate works and how we simulate it. What are some of the biggest misperceptions about climate models that you hear? One is that people say climate models are based on uncertain science. But that's not true at all. If we didn't know the science, my cellphone wouldn't work. Radios wouldn't work. GPS wouldn't work. That's because the energy that warms the Earth, which radiates from the Sun, and is absorbed and re-emitted by Earth's surface — and also by greenhouse gases in the atmosphere — is part of the same spectrum of radiation that makes up radio waves. If we didn't understand electromagnetic waves, we couldn't have created the technology we rely on today. The same is true for the science that underlies other aspects of climate models. (Learn more on page 38 of the book.) But we don't understand everything, right? We have understood the basic physics for hundreds of years. The last piece of it, the discovery that carbon dioxide warms the atmosphere, was put in place in the late 19th, early 20th century. Everything else — the laws of motion, the laws of thermodynamics — was all worked out between the 17th and 19th centuries. (Learn more on page 39 of the book.) We do still have uncertainty in our modeling systems. A big part of this book is about how scientists understand that uncertainty and actually embrace it as part of their work. If you know what you don't know and why, you can use that to better understand the whole climate system. Can we ever eliminate the uncertainty? Not entirely. In our book, we break down uncertainty into three categories: model uncertainty (How good are the models at reflecting how the Earth really works?), initial condition uncertainty (How well do we understand what the Earth system looks like right now?), and scenario uncertainty (What will future emissions look like?) To better understand, it might help to think about the uncertainty that would be involved if you had a computer model that could simulate making a pizza. Instead of trying to figure out what Earth's climate would look like in 50 or 100 years, this model would predict what your pizza would look like when it was done.  The first thing you want to know is how well the model reflects the reality of how a pizza is made. For example, does the model take into account all the ingredients you need to make the pizza, and how they will each evolve? The cheese melts, the dough rises, and the pepperoni shrinks. How well can the model approximate each of those processes? This is model uncertainty. The second thing you'd want to know is if you can input all the pizza's "initial conditions" into the model. Some initial conditions — like how many pepperoni slices are on the pizza and where — are easy to observe, but others are not. For example, kneading the pizza dough creates small pockets of air, but you don’t know exactly where they are. When the dough is heated, the air expands and forms big bubbles in the crust. If you can't tell the model where the air pockets are, it can't accurately predict where the crust bubbles will form when the pizza is baked. The same is true for a climate model. Some parts of the Earth, like the deep oceans and the polar regions, are not easy to observe with enough detail, leaving scientists to estimate what the conditions there are like and leading to the second type of uncertainty in the model results.  Finally, the pizza-baking model also has to deal with "scenario uncertainty," because it doesn't know how long the person baking the pizza will keep it in the oven, or at what temperature. Without understanding the choices the human will make, the model can't say for sure if the dough will be soft, crispy, or burnt. With climate models, over long periods of time, like a century, we've found that this scenario uncertainty is actually the dominant one. In other words, we don't know how much carbon dioxide humans around the world going to emit in the years and decades to come, and it turns out that that's what matters most.  (Learn more about uncertainty on page 10 of the book.) Any other misperceptions you frequently hear? People always say, "If we can't predict the weather next week, how can we know what the climate will be like in 50 years?" Generally speaking, we can't perfectly predict the weather because we don't have a full understanding of all the current conditions. We don't have observations for every grid point on a weather model or for large parts of the ocean, for example. But climate is not concerned about the exact weather on a particular day 50 or 100 years from now. Climate is the statistical distribution of weather, not a particular point on that distribution. Climate prediction is focused on the statistics of this distribution, and that is governed by conservation of energy and mass on long time scales, something we do understand. (Learn more on page 6 of the book. Read more common misperceptions at http://www.demystifyingclimate.org/misperceptions.) Did you learn anything about climate modeling while working on the book? My background is the atmosphere. I sat down and wrote the whole section on the atmosphere in practically one sitting. But I had to learn about the other aspects of models, the ocean and the land, which work really differently. The atmosphere has only one boundary, a bottom boundary. We just have to worry about how it interacts with mountains and other bumps on the surface. But the ocean has three hard boundaries: the bottom and the sides, like a giant rough bathtub. It also has a boundary with the atmosphere on the top. Those boundaries really change how the ocean moves. And the land is completely different because it doesn't move at all. Writing this book really gave me a new appreciation for some of the subtleties of other parts of the Earth System and the ways my colleagues model them. (Learn more on page 13 of the book.) What was the most fun part of writing the book for you? I think having to force myself to think in terms of analogies that are understandable to a variety of people. I can describe a model using a whole bunch of words most people don't use every day, like "flux." It was a fun challenge to come up with words that would accurately describe the models and the science but that were accessible to everyone.

Days of our lives are getting longer

June 16, 2016 | With the days at their longest this time of year, consider this: They're lingering a tiny bit more because of climate change. That's because the runoff from melting ice sheets and glaciers is indirectly slowing the planet's rotation. As the water makes its way to the tropics, it redistributes a fraction of Earth's mass from the poles to the equator. The gradual shifting of mass to the planet's widest circumference, where it has to be moved more than 20,000 miles for a full rotation, has the effect of almost imperceptibly slowing Earth's spin. Figure skaters use the same approach, lifting their arms above their heads to accelerate into a spin and extending them outward to slow down. An iceberg floats in Disko Bay, near Ilulissat, Greenland, on July 24, 2015. Runoff from melting ice sheets and glaciers is shifting the mass of the planet and slightly slowing Earth's rotation. (Photo by Saskia Madlener, NASA.) To be sure, this change in Earth's rotation is not something that most of us would notice, adding no more than about a couple of thousandths of a second to the length of a day over the course of a century. And it's just one contributor to a long-term slowdown in Earth's spin, which is also affected by the moon's gravitational influence on tides. The 24-hour day may be something we take for granted, but it averaged only about 23 hours during the time of the dinosaurs. Still, the slowing of Earth's rotation is a sign of climate change's far-reaching and sometimes surprising impacts on our environment.  "The components of our Earth system are connected in ways that are not obvious at first glance," said NCAR climate scientist John Fasullo. "The idea that the warming of the surface can be connected to the length of the day can seem very esoteric. But when you think about it, the strong physical ties become apparent. "One of the great challenges for scientists is to make these connections and understand how aspects of our environment that seem so different are, in fact, connected with each other," he added. Indeed, much of the research around NCAR has highlighted unexpected connections among different parts of our physical world. Some examples: The heat generated by everyday activities in large cities alters the jet stream, affecting temperatures across thousands of miles Proliferating populations of pine beetles that are devastating Rocky Mountain forests may also be influencing local temperature and precipitation patterns The opening and closing of the Bering Strait may have helped drive global climate patterns during ice ages over the past 100,000 years The peak of the solar cycle and its aftermath appear to have impacts on Earth's climate that resemble La Niña and El Niño events, influencing weather around the world Fast-growing coastal cities alter weather patterns, making it easier for air pollutants to accumulate during warm summer weather instead of being blown out to sea. "Understanding how these seemingly disparate processes are connected with each other is critically important to advancing Earth system science," said NCAR Director Jim Hurrell. "Equally important, however, is that this improved understanding is vital for anticipating events that can have enormous consequences for society." Writer/contact:David Hosansky, Manager of Media Relations

Future summers could regularly be hotter than the hottest on record

BOULDER — In 50 years, summers across most of the globe could regularly be hotter than any summer experienced so far by people alive today, according to a study by scientists at the National Center for Atmospheric Research (NCAR).  If climate change continues on its current trajectory, the probability that any summer between 2061 and 2080 will be warmer than the hottest on record is 80 percent across the world's land areas, excluding Antarctica, which was not studied. If greenhouse gas emissions are reduced, however, that probability drops to 41 percent, according to the study. "Extremely hot summers always pose a challenge to society," said NCAR scientist Flavio Lehner, lead author of the study. "They can increase the risk for health issues, but can also damage crops and deepen droughts. Such summers are a true test of our adaptability to rising temperatures." The study, which is available online, is part of an upcoming special issue of the journal Climatic Changethat will focus on quantifying the benefits of reducing greenhouse gas emissions. The research was funded by the U.S. National Science Foundation (NSF) and the Swiss National Science Foundation. If greenhouse gas emissions remain unabated. virtually every summer between 2061-2080 could be hotter than any in the historical record. (Image is in the public domain.) Simulating a range of summers The research team, which includes NCAR scientists Clara Deser and Benjamin Sanderson, used two existing sets of model simulations to investigate what future summers might look like. Both had been created by running the NCAR-based Community Earth System Model 15 times, with one assuming that greenhouse gas emissions remain unabated and the other assuming that society reduces emissions. The Community Earth System Model is funded by NSF and the U.S. Department of Energy. The simulations were run on the Yellowstone system at the NCAR-Wyoming Supercomputing Center. By using simulations that were created by running the same model multiple times, with only tiny differences in the initial starting conditions, the scientists could examine the range of summertime temperatures we might expect in the future for the "business-as-usual" and reduced-emissions scenarios. "This is the first time that the risk of record summer heat and its dependence on the rate of greenhouse gas emissions has been so comprehensively evaluated from a large set of simulations with a single state-of-the-art climate model," Deser said. The scientists compared the results to summertime temperatures recorded between 1920 and 2014 as well as to 15 sets of simulated summertime temperatures for the same historic period. By simulating past summers — instead of relying solely on observations — the scientists established a large range of temperatures that could have occurred naturally under the same conditions, including greenhouse gas concentrations and volcanic eruptions. "Instead of just comparing the future to 95 summers from the past, the models give us the opportunity to create more than 1,400 possible past summers," Lehner said. "The result is a more comprehensive and robust look at what should be considered natural variability and what can be attributed to climate change." Emissions cuts could yield big benefits The scientists found that between 2061 and 2080, summers in large parts of North and South America, central Europe, Asia, and Africa have a greater than 90 percent chance of being warmer than any summer in the historic record if emissions continue unabated. This means that virtually every summer would be as warm as the hottest to date. In some regions, the likelihood of summers being warmer than any in the historical record remained less than 50 percent, but in those places — including Alaska, the central U.S., Scandinavia, Siberia, and continental Australia — summer temperatures naturally vary a great deal, making it more difficult to detect the impact of climate change. Reducing emissions would lower the global probability that future summers will be hotter than any in the past, but the benefits would not be spread uniformly. In some regions, including the U.S. East Coast and large parts of the tropics, the probability would remain above 90 percent, even if emissions were reduced. But it would be a sizable boon for other regions of the world. Parts of Brazil, central Europe, and eastern China would see a reduction of more than 50 percentage points in the chance that future summers would be hotter than the historic range. Since these areas are densely inhabited, a large part of the global population would benefit significantly from climate change mitigation. “We've thought of climate change as 'global warming'; among what matters is how this overall warming affects conditions that hit people where they live,” said Eric DeWeaver, program director in NSF’s Division of Atmospheric and Geospace Sciences, which funds NCAR.  “Extreme temperatures pose risks to people around the globe. These scientists show the power of ensembles of simulations for understanding how these risks depend on the level of greenhouse gas emissions.” Lehner recently published another study looking at the overlay of population on warming projections. “It's often overlooked that the majority of the world's population lives in regions that will see a comparably fast rise in temperatures," he said.  About the article Title: Future risk of record-breaking summer temperatures and its mitigation Authors: Flavio Lehner, Clara Deser, and Benjamin M. Sanderson Publication: Climatic Change, DOI: 10.1007/s10584-016-1616-2 Writer:Laura Snider, Senior Science Writer

Bayes in Space! — NASA’s CO2 Measurements and Uncertainty Quantification

NASA's Orbiting Carbon Observatory-2 (OCO-2) mission is now actively collecting space-based measurements of atmospheric carbon dioxide (CO2). Data are collected with high spatial and temporal resolution and the data product includes both an estimate of column averaged CO2 dry air mole fraction (XCO2) and an estimate of uncertainty. In this talk we will take a look at how these estimates are obtained. As with any remote sensing method, the measurements are indirect. The OCO-2 instrument measures reflected sunlight in three spectral bands that make a single "sounding”.

Oceanography Brown Bag - Busecke

Time variable eddy mixing in the global Sea Surface Salinity maxima

Julius Busecke

Lamont-Doherty Earth Observatory

Abstract:

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