Climate & Climate Change

NCAR-based climate model gets a significant upgrade

BOULDER, Colo. — The National Center for Atmospheric Research (NCAR) has released an updated version of its flagship climate model to include a host of new capabilities — from a much more realistic representation of Greenland's evolving ice sheet to the ability to model in detail how crops interact with the larger Earth system to the addition of wind-driven waves on the model's ocean surface.The Community Earth System Model version 2 (CESM2) is an open-source community computer model largely funded by the National Science Foundation, which is NCAR's sponsor, and the U.S. Department of Energy's Office of Science.Released publicly last week, CESM2 builds on a succession of climate models, each cutting edge for their day, stretching back decades to a time when their software only simulated atmospheric circulation. By comparison, CESM2 includes interactions among the land, ocean, atmosphere, land ice, and sea ice, representing the many important ways the different parts of the Earth system interact."The breadth of the science questions we can tackle just significantly expanded; that's very exciting to me," said Jean-François Lamarque, who led the effort to develop CESM2 until recently. "Every time we release a new model we're providing a better tool to do the science. It's a more complicated tool, but the world is very complicated."The new capabilities of CESM2 include:An atmospheric model component that incorporates significant improvements to its turbulence and convection representations, which open the way for an analysis of how these small-scale processes can impact the climate. Improved ability to simulate modes of tropical variability that can span seasons and affect global weather patterns, including extreme precipitation over the western United States. These more realistic representations will allow researchers to better understand those connections and could lead to improved seasonal predictions. A land ice sheet model component for Greenland that can simulate the complex way the ice sheet moves — sluggish in the middle and much more quickly near the coast — and does a better job of simulating calving of the ice into the ocean.  A global crop model component that can simulate both how cropland affects regional climate, including the impacts of increased irrigation, and how the changing climate will affect crop productivity. The component also allows scientists to explore the impacts of increased use of fertilizers and greater concentrations of atmospheric carbon dioxide, which can spur plant growth.  A wave model component that simulates how wind creates waves on the ocean, an important mechanism for mixing of the upper ocean, which in turn affects how well the model represents sea surface temperatures. An updated river model component that simulates surface flows across hillsides and into tributaries before entering the main river channel. It also simulates the speed of water as it moves through the channel, along with water depth. A new set of infrastructure utilities that provide many new capabilities for easier portability, case generation and user customization, testing functionality, and greatly increased robustness and flexibility.A full list of updates with more technical descriptions can be found at http://www.cesm.ucar.edu/models/cesm2/whatsnew.html. This image from a global CESM2 historical simulation shows key aspects of the Arctic climate system. The speed at which simulated glacier ice flows over Greenland is represented, with warmer colors indicating faster speeds. The September 2005 sea ice concentration is depicted in grayscale, with white indicating higher ice concentrations. The time series of September mean sea ice extent simulated by CESM2 is in good agreement with the satellite observations provided by the National Snow and Ice Data Center for the late 20th century and early 21st century, with both showing the recent sea ice decline. (©UCAR. Image courtesy of Alice DuVivier, Gunter Leguy, and Ryan Johnson/NCAR. This image is freely available for media & nonprofit use.)Community-driven, continuously improvedWork on CESM2 began in earnest about five years ago, but scientists began tinkering with how to improve the model as soon as CESM1 was released in 2010. It's no different with CESM2."We've already started to think about what we can improve for CESM3," Lamarque said. "We know, for example, that we want to make the ocean model better to expand the kind of scientific questions it can be used to answer."Collaboration and input from the broader Earth system science community has always been at the heart of the complex model development facilitated by NCAR. For example, the land model component of the new CESM2 tapped the expertise of more than 50 researchers at 16 different institutions.CESM, which is freely available, is an important tool for Earth system science researchers across the United States and the globe who are studying everything from the predictability of seasonal droughts to accelerating sea level rise. The NCAR-based model is one of about a dozen leading climate models around the globe that scientists use to research the changing climate and contribute what they find to the Intergovernmental Panel on Climate Change.Because the Earth system is so complicated, and computing resources are so limited, the computer models used to simulate how Earth's climate behaves use a mix of equations that actually represent the physics, biology, and chemistry behind the processes that unfold in the Earth system — from evaporation to ozone formation to deforestation to sea ice melt — and "parameterizations," which simplify small-scale processes and estimate their impacts."CESM2 is representing much more of the physics than past models, and we are doing a much better job of it," said CESM Chief Scientist Gokhan Danabasoglu, who is now leading the model development effort. "There are numerous new capabilities in all component models as well as significant infrastructure improvements for flexibility and easier portability.”These improved equations allow the model to do an even better job replicating the real world."The model is our lab — the only laboratory we get when studying the climate," Lamarque said. "So it has to be close enough to the real world to be relevant."

Measuring snowfall in Antarctica

Antarctica is one of the snowiest and windiest places on Earth, making it difficult for researchers to measure the amount of snow that is falling, and then becoming part of, the Antarctic ice sheets. A team of researchers have set up the first advanced suite of snowfall measuring tools in this harsh environment. (Image: Scott Landolt.)June 5, 2018 | Less than a year ago, an iceberg the size of the state of Delaware calved off an Antarctic ice shelf into the Weddell Sea, taking the final step in the slow but inevitable march of the ice sheet toward the ocean.Observers have long tracked the ice sheets to the ocean's edge, but little is known about the origins of these frozen formations. Scientists are interested in determining how much snowfall is feeding the ice sheets, and whether that amount offsets the frozen water lost to the ocean each year. For researchers studying the impacts of global climate change on the polar ice sheets, this data could help predict the future of Antarctica’s ice — and the world's coastlines. According to the National Snow and Ice Data Center, if the Antarctic Ice Sheet ever fully melted without being replenished, global sea level would rise about 200 feet (60 meters)."We have a good idea of how much ice is being lost," said NCAR scientist Scott Landolt. "What we don’t have a good handle on is how much snow is accumulating to offset the ice loss."To find the answers, Landolt and his team have just set up the first suite of advanced snowfall measuring tools in Antarctica. The goal is to get a picture of the snowfall budget feeding the ice sheets that hold approximately 90 percent of the world’s ice. The project is funded by the National Science Foundation, which is NCAR’s sponsor.Going to the snowiest landscape on Earth was the research trip of a lifetime for Landolt, who has been conducting snowfall measurements in the United States for 20 years. "Antarctica is the holy grail of snowfall measurement," he said.Measuring falling snowWhen snow falls in Antarctica, a variety of factors can compress it into ice that then slowly crawls toward the ocean. To understand how much snow is contributing to the ice sheet, researchers must measure the amount of water actually frozen in the snowflakes, referred to as the liquid water equivalent. The liquid water equivalent is very challenging to measure, and until now there have been few attempts by Antarctic researchers to do so.The challenge arises as snow falls. It is lighter than rain and therefore more likely to fall along a path dictated by blowing wind. To make things more difficult, once a snowflake reaches the ground it could then be picked up by the wind and blown for miles before finally settling down.With collaborators Mark Seefeldt and Andrew Monaghan, both at the University of Colorado Boulder, Landolt had to design a system that can make the distinction between falling snow and blowing snow. The system also had to withstand hurricane-force winds and temperatures well below -40 degrees (Fahrenheit/Celsius). "We have refined our techniques over the years doing local research on snowfall measurement, and we know the cutting edge of technology for doing this," said Landolt. "Now we are going to take on the real challenge of doing this in ridiculously windy and ridiculously cold conditions and try to get meaningful data out of that."A snowfall data collecting station includes a bucket on a mass balance inside a precipitation gauge, surrounded by two concentric wind shields to help guide the snow into the mouth of the gauge. (Image: Scott Landolt.)Handling extreme conditionsIn November 2017, Landolt and his team, which included technical support from UNAVCO, set up a suite of specially tailored snow measurement tools at four precipitation monitoring stations in Antarctica. The tools measure snow height, snow mass (to determine the liquid water equivalent), snowflake size, wind speed, and the number of snowflakes that fall in a given amount of time. The researchers also set up a webcam to keep an eye on their weather stations. The entire suite runs on just three watts of power per year, the equivalent of powering a small light bulb for the same amount of time.Snow mass is the key measurement that helps researchers estimate the liquid water equivalent going into the ice sheet. These data are collected using a bucket inside a precipitation gauge that sits on a very sensitive mass balance. The precipitation gauge is encircled by two concentric wind shields designed to slow wind down, minimizing gusting winds that can blow the snow around and over the bucket. The shields help direct the snow to fall into the gauge. Once snow has accumulated in the bucket, the researchers can measure the mass and convert it to the liquid water equivalent.Preliminary measurements from the sites are already revealing more of the Antarctic’s story. Landolt’s team noticed that after a snowfall event, the measurement devices show signs of snow sublimating — the process of going directly from solid snowflakes to water vapor. Landolt pointed to an example of a snowfall that accumulated 0.2 inches of liquid water equivalent, but then slowly sublimated out over the course of two weeks. This could mean that less Antarctic snow may be feeding ice sheets than previously thought."This is one cool thing about the project that we did not set out to measure but we will report on," said Landolt. "There have been estimates of how much snow is sublimating, but to my knowledge, nobody has actually really measured this before."The team has two more trips to the Antarctic sites scheduled: a maintenance trip later this year, and a tentative sensor removal trip in 2019. If the data from the weather stations is sound, the next step would be to integrate the technology into existing Antarctic weather stations. Once the data is analyzed, the team expects this work to help climate scientists adjust models of climate change and sea level rise."If this works, the goal would be to get more stations across Antarctica, which would contribute to more accurate snowfall modeling," said Landolt. "There are worldwide impacts to the research we are doing."The team of researchers set up four precipitation measuring stations in Antarctica, complete with a suite of tools to measure snow height, snow mass, snowflake size, wind speed, and number of snowflakes falling in a time period. (Image: Scott Landolt.)Collaborators:Andrew Monaghan, University of Colorado BoulderMark Seefeldt, University of Colorado BoulderNikko Bayou, UNAVCO
Spenser Niebuhr, UNAVCO
Thomas Nylen, UNAVCOFunder:
National Science FoundationWriter/Contact:
Alexandra Branscombe

Hurricanes: A bit stronger, a bit slower, and a lot wetter in a warmer climate

BOULDER, Colo. — Scientists have published a detailed analysis of how 22 recent hurricanes would change if they instead formed near the end of this century. While each storm's transformation would be unique, on balance, the hurricanes would become a little stronger, a little slower moving, and a lot wetter.In one example, Hurricane Ike — which killed more than 100 people and devastated parts of the U.S. Gulf Coast in 2008 — could have 13 percent stronger winds, move 17 percent slower, and be 34 percent wetter if it formed in a future, warmer climate.Other storms could become slightly weaker (like Hurricane Ernesto) or move slightly faster (like Hurricane Gustav). None would become drier. The rainfall rate of simulated future storms in the study increased by an average of 24 percent.The study, led by the National Center for Atmospheric Research (NCAR) and published in the Journal of Climate, compares high-resolution computer simulations of more than 20 historical, named Atlantic storms with a second set of simulations that are identical except for a warmer, wetter climate that is consistent with the average outcome of scientific projections for the end of this century."Our research suggests that future hurricanes could drop significantly more rain," said NCAR scientist Ethan Gutmann, who led the study. "Hurricane Harvey demonstrated last year just how dangerous that can be."Harvey produced more than four feet of rain in some locations, breaking records and causing devastating flooding across the Houston area.The research was funded by the National Science Foundation, which is NCAR's sponsor, and by DNV GL (Det Norske Veritas Germanischer Lloyd), a global quality assurance and risk management company.This infographic shows how 22 named storms would change if they formed at the end of this century instead of toward the beginning. Each individual storm changed in a unique way, with some getting weaker or faster instead of stronger or slower. All became wetter. To see a larger version of this graphic, click here. (©UCAR. Graphic by Simmi Sinha. This image is freely available for media & nonprofit use.)  Tapping a vast data set to see stormsWith more people and businesses relocating near the coasts, the potential influence of climate change on hurricanes has significant implications for public safety and the economy. Last year's hurricane season, which caused an estimated $215 billion in losses according to Munich RE, was the costliest on record."This study shows that the number of strong hurricanes, as a percent of total hurricanes each year, may increase," said Ed Bensman, a program director in the National Science Foundation’s Division of Atmospheric and Geospace Sciences, which supported the study. "With increased development along coastlines, that has important implications for future storm damage."It's been challenging for scientists to study how hurricanes may change in the future as the climate continues to warm. Most climate models, which are typically run on a global scale over decades or centuries, are not run at a high enough resolution to "see" hurricanes.Most weather models, on the other hand, are run at a high enough resolution to accurately represent hurricanes, but they generally are not used to simulate long-term changes in climate due to the high cost of computational resources.For the current study, the researchers took advantage of a massive new data set created at NCAR by running the Weather Research and Forecasting (WRF) model at a high resolution (4 kilometers, or about 2.5 miles) over the contiguous United States over two 13-year periods. The simulations took about a year to run at the NCAR-Wyoming Supercomputing Center in Cheyenne.The first set of model runs simulates the weather as it unfolded between 2000–2013 and the second simulates the same weather patterns, but in a climate that is about 5 degrees Celsius (9 degrees Fahrenheit) hotter — the amount of warming expected by end of century if greenhouse gas emissions continue unabated.The scientists created an algorithm to detect and track hurricanes within the vast amount of data. They identified 22 named storms that appear with very similar tracks in both the historic and future simulations, allowing them to be more easily compared.As a group, the storms in the future simulation had 6 percent stronger average hourly maximum wind speeds than those in the past. They also moved at a 9 percent slower speed and had a 24 percent higher average hourly maximum rainfall rate.  Average storm radius did not change.But each storm was unique."Some past studies have also run WRF at a high resolution to study the impact of climate change on hurricanes, but those studies have tended to look at a single storm, like Sandy or Katrina," Gutmann said. "What we find looking at more than 20 storms is that some change one way, while others change in a different way. There is so much variability that you can't just study one storm and then extrapolate to all storms."Still, there was one consistent feature across storms: They all produced more rain.While the study sheds light on how a particular storm might look in a warmer climate, it doesn't provide insight into how global warming might affect storm genesis. That's because the hurricanes analyzed in this study formed outside of the region simulated by WRF and passed into the WRF simulation as fully formed storms.Other research has suggested that fewer storms may form in the future due to increasing atmospheric stability or greater high-level wind shear, though the storms that do form are apt to be stronger."It's possible that in a future climate, large-scale atmospheric changes would make it so that some of these storms might never be able to form," Gutmann said. "But from this study we get an idea of what we can expect from the storms that do form."The study co-authors include NCAR scientists Roy Rasmussen, Changhai Liu, Kyoko Ikeda, Cindy Bruyere, and James Done, as well as Luca Garrè, Peter Friis-Hansen, and Vidyynmala Veldore, all of DNV GL.About the articleTitle: Changes in Hurricanes from a 13-Yr Convection-Permitting Pseudo-Global Warming SimulationAuthors: Ethan D. Gutmann, Roy M. Rasmussen, Changhai Liu, Kyoko Ikeda, Cindy L. Bruyere, James M. Done, Luca Garrè, Peter Friis-Hansen, and Vidyunmala VeldoreJournal: Journal of Climate, DOI: 10.1175/JCLI-D-17-0391.1Writer:Laura Snider, Senior Science Writer

Record-breaking ocean heat fueled Hurricane Harvey

BOULDER, Colo. — In the weeks before Hurricane Harvey tore across the Gulf of Mexico and plowed into the Texas coast in August 2017, the Gulf's waters were warmer than any time on record, according to a new analysis led by the National Center for Atmospheric Research (NCAR).These hotter-than-normal conditions supercharged the storm, fueling it with vast stores of moisture, the authors found. When it stalled near the Houston area, the resulting rains broke precipitation records and caused devastating flooding."We show, for the first time, that the volume of rain over land corresponds to the amount of water evaporated from the unusually warm ocean," said lead author Kevin Trenberth, an NCAR senior scientist. "As climate change continues to heat the oceans, we can expect more supercharged storms like Harvey."Despite a busy 2017 hurricane season, Hurricane Harvey was more or less isolated in location and time, traveling solo over relatively undisturbed waters in the Gulf of Mexico. This gave Trenberth and his colleagues an opportunity to study in detail how the storm fed off the heat stored in that 930-mile wide ocean basin.The team compared temperatures in the upper 160 meters (525 feet) of the Gulf before and after the storm using data collected by Argo, a network of autonomous floats that measure temperature as they move up and down in the water. To measure rainfall over land, the scientists took advantage of a new NASA-based international satellite mission, dubbed Global Precipitation Measurement.The study appears in the journal Earth's Future, a publication of the American Geophysical Union. It was funded by the U.S. Department of Energy and by the National Science Foundation, which is NCAR's sponsor. Other co-authors of the paper are Yongxin Zhang and John Fasullo, also of NCAR; Lijing Cheng, of the Chinese Academy of Sciences; and Peter Jacobs, of George Mason University.An image of Hurricane Harvey taken by the GOES-16 satellite as the storm collided with the Texas coast. (Image courtesy NASA.) Matching evaporation and rainAs hurricanes move over the ocean, their strong winds strafe the sea surface, making it easier for water to evaporate. The process of evaporation also requires energy from heat, and the warmer the temperatures are in the upper ocean and at the ocean surface, the more energy is available.As the storm progresses over the ocean, evaporating water as it goes, it leaves a cold wake in its path. In the case of Hurricane Harvey, the scientists found the cold wake was not very cold. So much heat was available in the upper layer of the ocean that, as the surface temperature was cooled from the storm, heat from below welled up, rewarming the surface waters and continuing to feed the storm.The near-surface ocean temperature before the storm's passage was upward of 30 degrees Celsius (86 degrees Fahrenheit), and after passage the temperature was still around 28.5 C (83 F). Sea surface temperatures above 26 C (79 F) are typically needed for a hurricane to continue to grow.Even after Harvey made landfall, its arms reached out over the ocean, continuing to draw strength (and water) from the still-warm Gulf."The implication is that the warmer oceans increased the risk of greater hurricane intensity and duration," Trenberth said. "While we often think of hurricanes as atmospheric phenomena, it's clear that the oceans play a critical role and will shape future storms as the climate changes."The scientists were able to measure the total loss in ocean heat, mostly due to evaporation, as the storm moved over the Gulf. They also measured the latent heat released over land as the water vapor turned back into liquid water and fell as rain. They then compared those two measurements and found that they corresponded.The study highlights the increased threat of future supercharged hurricanes due to climate change, Trenberth said."We know this threat exists, and yet in many cases, society is not adequately planning for these storms," Trenberth said. "I believe there is a need to increase resilience with better building codes, flood protection, and water management, and we need to prepare for contingencies, including planning evacuation routes and how to deal with power cuts."About the studyTitle: Hurricane Harvey Links to Ocean Heat Content and Climate Change AdaptationAuthors: Kevin E. Trenberth, Lijing Cheng, Peter Jacobs, Yongxin Zhang, and John FasulloJournal: Earth's Future. DOI: 10.1029/2018EF000825Writer:Laura Snider, Senior Science Writer

Reconciling Paris Agreement goals for temperature, emissions

As society faces the challenge of limiting warming to no more than 2 degrees Celsius, new research finds an apparent contradiction: Achieving that goal doesn't necessarily require cutting greenhouse gas emissions to zero, as called for in the Paris Agreement. But under certain conditions, even zero emissions might not be enough.The Paris Agreement, a global effort to respond to the threats of human-caused climate change, stipulates that warming be limited to between 1.5 degrees C (2.7 degrees Fahrenheit) and 2 degrees C (3.6 degrees F). It also stipulates that countries achieve net-zero greenhouse gas emissions in the second half of this century. But the relationship between the two — is the emissions goal sufficient or even necessary to meet the temperature goal? — has not been well understood.In a new study published in the journal Nature Climate Change, scientists used a computer model to analyze a variety of possible future scenarios to better understand how emissions reductions and temperature targets are connected. The study, published March 26, was led by Katsumasa Tanaka at the National Institute for Environmental Studies in Japan and co-authored by Brian O'Neill at the U.S. National Center for Atmospheric Research."What we found is that the two goals do not always go hand in hand," Tanaka said. "If we meet temperature targets without first overshooting them, we don't have to reduce greenhouse gas emissions to zero. But if we do reduce emissions to zero, we still might not meet the temperature targets if we don't reduce emissions quickly enough."The team also found that whether temperatures overshoot the target temporarily has a critical impact on the scale of emissions reductions needed."If we overshoot the temperature target, we do have to reduce emissions to zero. But that won’t be enough," Tanaka said. "We'll have to go further and make emissions significantly negative to bring temperatures back down to the target by the end of the century."The research was supported by the Environment Research and Technology Development Fund (2-1702) of the Environmental Restoration and Conservation Agency in Japan and by the U.S. National Science Foundation, NCAR's sponsor.Drafted in 2015, the Paris Agreement has been ratified by more than 170 countries. President Donald Trump announced last year the intention to withdraw the United States from the agreement.Modeling the problem from both sidesFor the study, the researchers used a simplified integrated assessment model that takes into account the physical connections between greenhouse gases and global mean temperature in the climate as well as the economic costs of emissions reductions."We investigated the consistency between the Paris targets in two ways. First we asked, what happens if you just meet the temperature target in a least-cost way? What would emissions look like?" said O'Neill, an NCAR senior scientist. "Then we said, let's just meet the emissions goal and see what kind of temperatures you get."The team generated 10 different scenarios. They found that Earth's warming could be stabilized at 1.5 or 2 degrees C — without overshooting the goal — by drastically cutting emissions in the short term. For example, total greenhouse gas emissions would need to be slashed by about 80 percent by 2033 to hit the 1.5-degree target or by about two-thirds by 2060 to meet the 2-degree target. In both these cases, emissions could then flatten out without ever falling to zero.Due to the difficulty of making such steep cuts, the scientists also looked at scenarios in which the temperature was allowed to temporarily overshoot the targets, returning to 1.5 or 2 degrees by the end of the century. In the 1.5-degree overshoot scenario, emissions fall to zero by 2070 and then stay negative for the rest of the century. (Negative emissions require activities that draw down carbon dioxide from the atmosphere.) For the 2-degree temporary overshoot scenario, emissions fall to zero in 2085 and also become negative, but for a shorter period of time.On the flip side, the scientists also looked at scenarios where they set the emissions levels instead of the temperature. In those cases, they analyzed what would happen if emissions were reduced to zero around mid-century (2060) or at the end of the century (2100). In the first case, the global temperature peaked around the 2-degree target and then declined. But in the second case, the temperature rose above 2 degrees around 2043 and stayed there for a century or more."The timing of when emissions are reduced really matters," O'Neill said. "We could meet the goal set out in the Paris Agreement of reducing emissions to zero in the second half of the century and still wildly miss the temperature targets in the same agreement if we wait to take action."The new study is part of a growing body of research that seeks to better understand and define what it will take to comply with the Paris Agreement. For example, another recent study — led by Tom Wigley, a climate scientist at the University of Adelaide who holds an honorary appointment at NCAR — also looks at the quantity and timing of emissions cuts needed to stabilize global temperature rise at 1.5 or 2 degrees above preindustrial levels. This work focuses in particular on implications for emissions of carbon dioxide, the main component of the broader greenhouse gas emissions category that makes up the Paris emissions target.O'Neill and Tanaka believe their work might be useful as countries begin to report the progress they've made reducing their emissions and adjust their goals. These periods of reporting and readjusting, known as global stocktakes, are formalized as part of the Paris Agreement and occur every five years."Our study and others may help provide countries with a clearer understanding of what work needs to be done to meet the goals laid out in the agreement. We believe that the Paris Agreement needs this level of scientific interpretation," Tanaka said.

Cutting greenhouse gas emissions would help spare cities worldwide from rising seas

BOULDER, Colo. — Coastal cities worldwide would face a reduced threat from sea level rise if society reduced greenhouse gas emissions, with especially significant benefits for New York and other U.S. East Coast cities, new research indicates.The study, by scientists at the National Center for Atmospheric Research (NCAR), used a powerful computer model to tease out the ways that winds and currents in a warming world push ocean water around, lifting it in some regions and lowering it in others. The scientists examined how these variations in sea level rise would change under two conditions: if emissions continue on their current trajectory, or if they are sharply reduced.The results showed that, if society can implement cuts soon on emissions of carbon dioxide and other heat-trapping gases, the projected increases in sea level around the globe would be significantly less toward the end of the century. This would help coastal cities in much of the world as they try to fend off rising waters, with the benefits most pronounced for cities on parts of the Atlantic and Indian oceans.Projected sea level rise for major cities worldwide will vary significantly later this century, depending on whether society continues to increase emissions of greenhouse gases at the current rate (a scenario known as RCP 8.5) or begins to sharply reduce them (RCP 4.5). Some cities, such as New York and London, would see particularly pronounced benefits if society cuts emissions. For more details on the range of projected sea level rise for major cities, click on the graphic or see table below. (Graphic by Simmi Sinha, ©UCAR. Click to enlarge. This graphic is freely available for media & nonprofit use.)  "Mitigating greenhouse gases will reduce sea level rise later this century, with some regions seeing especially significant benefits," said NCAR scientist Aixue Hu, the lead author of the new study. "As city officials prepare for sea level rise, they can factor in the compounding effect of local conditions, which are due to the winds and currents that cause internal variability in the oceans."Hu and his co-author, NCAR scientist Susan Bates, caution that the modeling study presents an incomplete picture, because it does not include runoff from melting ice sheets and glaciers — two factors that scientists are just now incorporating into computer models. Instead, it simulates the influence of climate change on variations in sea level worldwide to reveal which coastlines will benefit most from emission reductions associated with the additional heat absorbed by the ocean.The study, published this month in the journal Nature Communications, was funded by the U.S. Department of Energy and by the National Science Foundation, which is NCAR's sponsor.Global changes with local impactsSea level rise is one of the most consequential impacts of climate change, threatening to swamp low-lying islands and major coastal cities. Sea levels in some regions are expected to rise by several feet by the end of this century, due to a combination of melting ice sheets and glaciers (which account for about two-thirds of sea level rise) along with thermal expansion, or ocean waters expanding as they warm (which accounts for the remaining one-third).To study how changes in emissions would affect global sea level rise and local variations, Hu and Bates used two sets of computer simulations that are based on two different greenhouse gas scenarios.In the business-as-usual scenario, with emissions from human activity continuing to increase at current rates, global temperatures by late this century would rise by about 5.4 degrees Fahrenheit (3 degrees Celsius) over late 20th century levels. In the moderate mitigation scenario, with society taking steps to reduce greenhouse gases, warming would be held to about 3.2 degrees F (1.8 degrees C).The scientists found that reducing greenhouse gas emissions would not significantly restrain sea level rise for the next two decades. The reason, in part, has to do with the inertia of the climate system (once heat enters the oceans, it is retained for a period of time). In addition, winds and currents are naturally variable from year to year, pushing ocean water in different directions and making it hard to discern the full impact of planet-scale warming over the span of a decade or two.But the scientists found that later in the century, from 2061 to 2080, reduced emissions would have a significant impact across almost the entire world. The simulations showed that the extent of mean global sea level rise from thermal heat expansion (but not runoff from melting ice) was reduced by about 25 percent, from about 17.8 centimeters (7 inches) in the business-as-usual scenario to 13.2 centimeters (5.2 inches) in the moderate mitigation scenario.Locally, winds and currents make a differenceFor some cities, the benefits of the lower-emission scenario would be especially significant. New York City, where sea levels this century are expected to rise more than almost anywhere else in the world, would see a difference of 9.8 centimeters (3.9 inches). Other cities that would see a greater-than-average reduction include Boston (9.3 cm/3.7 in), London (8.3 cm/3.3 in), Dar es Salaam (6.8 cm/2.7 in), Miami (6.5 cm/2.6 in), and Mumbai (5.8 cm/2.3 in).On the other hand, some cities in South America (such as Buenos Aires), Asia (such as Bangkok and Jakarta), Australia (such as Melbourne), and the west coast of North America (such as Vancouver and San Francisco) would see lower-than-average benefits. And reducing greenhouse gases would have no statistically significant effect on sea level rise along the western coasts of Australia and the Philippines.The reason for the local differences in sea level rise has to do with the influence (or lack thereof) of a changing climate on major currents and on atmosphere-ocean interactions around the globe.In the northern Atlantic, for example, warming temperatures are expected to weaken the Gulf Stream that transports warmer water from the subtropics to the Arctic. The powerful current draws water away from much of the east coast of the United States, and scientists have warned that a weakening current would send those waters back toward the coastline and significantly raise sea levels. If actions taken by society resulted in reduced emissions, the Gulf Stream would be less affected and, therefore, sea level rise in the north Atlantic would be less substantial.In contrast, the currents in some other ocean basins appear to be less sensitive to climate change. Across much of the Pacific, for example, sea levels are influenced by the Pacific Decadal Oscillation, a phenomenon related to winds and sea surface temperatures. Although climate change is affecting winds and causing sea surface temperatures to rise in the Pacific, it is not disrupting currents there as much as it is in the northern Atlantic. As a result, climate change mitigation that reduces thermal expansion would generally have a less significant effect on Pacific sea levels.The study also found greater variations in future sea level rise in different regions, including some cities where local sea levels are influenced by the Pacific Decadal Oscillation or by an Atlantic climate pattern known as the North Atlantic Oscillation. As a result, the projected sea level rise in the model varied more for London and Tokyo than for New York."City planners in some places will be able to make decisions based on more certain sea level projections, but for other places it's going to be more difficult to know what the sea levels will be," Bates said.About the paperTitle: Internal climate variability and projected future regional steric and dynamic sea level rise
Authors: Aixue Hu and Susan BatesJournal: Nature CommunicationsNew research estimates the extent to which sea level rise would be reduced for major cities worldwide by later this century if society cuts emissions of greenhouse gas emissions. These tables incorporates projections based on the thermal expansion of ocean water as well as on the localized impacts of winds and currents, but they do not include additional sea level rise caused by the melting of ice sheets and glaciers. (Data produced by Aixue Hu and Susan Bates, NCAR. Graphic by Simmi Sinha, UCAR. Click to enlarge. This graphic is freely available for media & nonprofit use.)

The rate of sea level rise is accelerating, a new study finds

NCAR scientist John Fasullo is a co-author of a new study appearing in the Proceedings of the National Academies of Science. The study finds that the rate of sea level rise is accelerating. The following is an excerpt from a news release by the Cooperative Institute for Research in Environmental Sciences. February 13, 2018 | Global sea level rise is not cruising along at a steady 3 mm per year. It’s accelerating a little every year, according to a new study that harnessed 25 years of satellite data to calculate that the rate is increasing by about 0.08 mm/year every year — which could mean an annual rate of sea level rise of 10 mm/year, or even more, by 2100.“This acceleration, driven mainly by accelerated melting in Greenland and Antarctica, has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate—to more than 60 cm instead of about 30.” said lead author Steve Nerem, a scientists at the Cooperative Institute for Research in Environmental Sciences. "And this is almost certainly a conservative estimate," he added. "Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years. Given the large changes we are seeing in the ice sheets today, that's not likely."If the oceans continue to change at this pace, sea level will rise 65cm (26 inches) by 2100—enough to cause significant problems for coastal cities, according to the new assessment by Nerem and several colleagues from CU Boulder, the University of South Florida, NASA Goddard Space Flight Center, Old Dominion University, and the National Center for Atmospheric Research. The team, driven to understand and better predict Earth’s response to a warming world, published their work today in the journal Proceedings of the National Academy of Sciences.Rising concentrations of greenhouse gases in Earth’s atmosphere increase the temperature of air and water, which causes sea level to rise in two ways. First, warmer water expands, and this "thermal expansion" of the oceans has contributed about half of the 7 cm of global mean sea level rise we've seen over the last 25 years, Nerem said. Second, melting land ice flows into the ocean, also increasing sea level across the globe.These increases were measured using satellite altimeter measurements since 1992, including the U.S./European TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 satellite missions. But detecting acceleration is challenging, even in such a long record. Episodes like volcanic eruptions can create variability: the eruption of Mount Pinatubo in 1991 decreased global mean sea level just before the Topex/Poseidon satellite launch, for example. In addition, global sea level can fluctuate due to climate patterns such as El Niños and La Niñas (the opposing phases of the El Niño Southern Oscillation, or ENSO) which influence ocean temperature and global precipitation patterns.Read the full news release here. 

Drier and wetter: The future of precipitation variability

January 17, 2018 | Precipitation variability — the swing from dry to wet and back again — will continue to increase across the majority of the world's land area as the climate warms, according to a new study led by scientists at the National Center for Atmospheric Research.The researchers expect precipitation variability to become greater from day to day, year to year, and even decade to decade. The new research, published in the Nature journal Scientific Reports, provides results from sophisticated computer simulations that predict that there will be both more droughts and more floods within the same areas as the climate warms. The findings are relevant for water managers who need to make long-range plans."When it's dry, it will be drier. When it's wet, it will be wetter — in the same place," said NCAR scientist Angeline Pendergrass, lead author of the study. "There will be a broader range of conditions that will become 'normal.'"The research was funded by the National Science Foundation, which is NCAR's sponsor, and by the U.S. Department of Energy.As the climate continues to warm, the range of precipitation that is "normal" in a particular place is likely to grow, meaning a single location can become both wetter and drier. The image on the left shows a flood in Colorado. The image on the right shows a droughtin Texas. (Images courtesy the U.S. Department of Defense and U.S. Department of Agriculture.)New tools to study changes in precipitationHistorically, changes in precipitation variability have been difficult to pin down because the amount of rain or snow a particular region gets can vary a great deal naturally.But in recent years, the availability of large ensembles of climate model runs has allowed scientists to begin separating some of the more subtle impacts of climate change from the natural chaos in the climate system. These ensembles may include 30 or 40 runs of a single climate model over the same time period with slightly different, but equally plausible, initial conditions.Pendergrass and her colleagues, NCAR scientists Flavio Lehner, Clara Deser, and Benjamin Sanderson, along with ETH-Zürich professor Reto Knutti, took a closer look at precipitation variability using large ensembles of runs from the NCAR-based Community Earth System Model (CESM) and from the Geophysical Fluid Dynamics Laboratory (GFDL) climate model. They also looked at a collection of individual runs taken from many different climate models and known as the Climate Model Intercomparison Project Phase 5, or CMIP5.The team found that precipitation variability will likely increase substantially over two-thirds of the world's land areas by the end of the century if greenhouse gas emissions continue unabated. They also found that, on average, variability increases 4 to 5 percent over land per degree Celsius of warming and that variability increases across all time scales, from days to decades."This increase in variability is arising due to more moisture in the atmosphere and a weakening of global atmospheric circulation," Pendergrass said. "That's important because it means that changes in precipitation variability are not just linked to changes in El Niño and La Niña events, as some previous work implied."Helping water managers plan for the futurePendergrass hopes the study's findings will be used by water managers in their future planning. Models used today by water managers often assume that the change in precipitation variability in the future will track with the expected increase in average precipitation.But the new study finds that the increase in precipitation variability will outstrip the increase in average precipitation, which means that water managers may be miscalculating the magnitude of future swings from wet to dry or vice versa."Water managers may be underestimating how much heavy events — floods or droughts — will change," Pendergrass said.About the articleTitle: Precipitation variability increases in a warmer climateAuthors: Pendergrass, A. G., R. Knutti, F. Lehner, C. Deser, and B. M. SandersonJournal: Scientific Reports, DOI: 10.1038/s41598-017-17966-yWriter/contact:Laura Snider, Senior Science Writer

The climate secrets of southern clouds

BOULDER, Colo. — This month, an international team of scientists will head to the remote Southern Ocean for six weeks to tackle one of the region's many persistent mysteries: its clouds.What they discover will be used to improve climate models, which routinely underestimate the amount of solar radiation reflected back into space by clouds in the region. Accurately simulating the amount of radiation that is absorbed or reflected on Earth is key to calculating how much the globe is warming.The field campaign, called the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study, or SOCRATES, could also help scientists understand the very nature of how clouds interact with aerosols — particles suspended in the atmosphere that can be from either natural or human-made sources. Aerosols can spur cloud formation, change cloud structure, and affect precipitation, all of which affect the amount of solar radiation that is reflected.During the mission, which will run from mid-January through February, the scientists will collect data from a bevy of advanced instruments packed onboard an aircraft and a ship, both of which are specially designed for scientific missions."SOCRATES will allow for some of the best observations of clouds, aerosols, radiation, and precipitation that have ever been collected over the Southern Ocean," said Greg McFarquhar, a principal investigator and the director of the University of Oklahoma Cooperative Institute for Mesoscale Meteorological Studies (CIMMS). "These data will provide us with critical insight into the physics of cloud formation in the region, information we can use to improve global climate models."The U.S. portion of SOCRATES is largely funded by the National Science Foundation (NSF).“The Southern Ocean is famously remote and stormy and it's hard to imagine a worse place to do a field campaign. But a vast, stormy ocean is a great laboratory for studying clouds, and it's clear from our models that we have a lot to learn about them,” said Eric DeWeaver, program director for Climate and Large-Scale Dynamics in NSF’s Geoscience directorate."I'm excited about this campaign because I think it will answer some fundamental questions about clouds and their dependence on atmospheric conditions," DeWeaver said. "We'll be able to use this information to understand cloud behavior closer to home and how clouds are likely to adjust to changing climatic conditions."Critical observing and logistical support for SOCRATES is being provided by the Earth Observing Laboratory (EOL) at the National Center for Atmospheric Research (NCAR). Other U.S. principal investigators are based at the University of Washington.The Australian portion of SOCRATES is largely funded by the country's government through the Australian Marine National Facility, which is owned and operated by CSIRO.A supercooled mysteryMcFarquhar and his colleagues think the reason that climate models are not accurately capturing the amount of radiation reflected by clouds above the Southern Ocean is because they may not be correctly predicting the composition of the clouds. In particular, the models may not be producing enough supercooled water — droplets that stay liquid even when the temperature is below freezing.One possible explanation for the problem is the way models represent how clouds interact with aerosols, a process that affects the amount of supercooled water in a cloud. These representations were developed from atmospheric observations, largely in the Northern Hemisphere, where most of the world's population lives.But the atmosphere over the Northern Hemisphere — even over the Arctic — contains many more pollutants, including aerosols, than the atmosphere over the Southern Ocean, which is relatively pristine."We don't know how appropriate the representations of these processes are for the Southern Hemisphere," McFarquhar said. "SOCRATES will give us an opportunity to observe these cloud-aerosol interactions and see how much they differ, if at all, from those in the Northern Hemisphere."Flying through hazardous cloudsThe NSF/NCAR HIAPER Gulfstream V has been modified to serve as a flying laboratory. (©UCAR. This figure is freely available for media & nonprofit use.)For the SOCRATES field campaign, observations will be taken from the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research, or HIAPER, a highly modified Gulfstream V aircraft, and the R/V Investigator, an Australian deep-ocean research vessel."Much of what we currently know about Southern Ocean cloud, aerosol, and precipitation properties comes from satellite-based estimates, which are uncertain and have undergone few comparisons against independent data," said co-investigator Roger Marchand, a scientist at the University of Washington. "The data collected during SOCRATES will also enable us to evaluate current satellite data over the Southern Ocean, as well as potentially help in the design of better satellite-based techniques."The research aircraft will be based out of Hobart, Tasmania, and will make about 16 flights over the Southern Ocean during the course of the campaign. The many high-tech instruments on board will measure the size and distribution of cloud droplets, ice crystals, and aerosols, as well as record the temperature, winds, air pressure, and other standard atmospheric variables.The instruments include NCAR's HIAPER Cloud Radar (HCR) and High Spectral Resolution Lidar (HSRL). The wing-mounted HCR is able to "see" inside clouds and characterize the droplets within, while the HSRL can measure air molecules and aerosols. Together, the two highly advanced instruments will give scientists a more complete picture of the wide range of particles in the atmosphere above the Southern Ocean.The nature of the research — flying a plane in search of supercooled water —presents some challenges with aircraft icing."Oftentimes, the cleaner the air, the more probable large drops and severe icing conditions become," said Cory Wolff, the NCAR project manager who is overseeing aircraft operations for SOCRATES. "We have a number of precautions we're taking to mitigate that risk."First, a mission coordinator whose sole job is to monitor icing conditions will join each flight. Second, the design of the flights themselves will help the crew anticipate icing conditions before they have to fly through them. On the flight south from Tasmania, the HIAPER GV will fly high above the clouds — and the icing danger. During that leg of the flight, the scientists will collect information about the clouds below, both with onboard radar and lidar as well as with dropsondes — small instrument packages released from the aircraft.With that information, the scientists can determine whether it's safe to pilot the aircraft through the clouds on the return trip, collecting detailed information about the cloud composition.Sailing the stormiest seasThe Australian R/V Investigator will take measurements of the atmosphere and ocean during its six-week voyage. (Image courtesy CSIRO.)The measurements taken from the sky will be complemented by data collected from instruments on board the Australian R/V Investigator, including the NCAR Integrated Sounding System. The ISS gathers extensive data by using a radar wind profiler, surface meteorology sensors, and a balloon-borne radiosonde sounding system. The team will launch soundings every six hours, and sometimes more often, throughout the campaign."Observations from the ship will help us understand the background state of the atmosphere — how it's behaving," said NCAR scientist Bill Brown, who traveled to Australia in late November to prepare the ISS for the voyage.The ship will be deployed for the entire six weeks and will face its own challenges, notably the notorious roughness of the Southern Ocean, sometimes called the stormiest place on Earth."There are no land masses to break up the winds down there," Brown said. "So the ocean can be quite rough."SOCRATES investigators will also draw on measurements from another Australian ship as it travels between Tasmania and Antarctica on resupply missions, the R/V Aurora Australis, as well as observations from buoys and some land-based instruments on Macquarie Island."I am excited that we will have such a comprehensive suite of observations," McFarquhar said. "If we just had the cloud observations we wouldn’t have the appropriate context. If we just had the aerosols and measurements below the clouds, we wouldn't be able to understand the complete picture."For more about the SOCRATES campaign, visit the project website.Collaborating institutions:Australian Antarctic DivisionAustralian Bureau of MeteorologyAustralian Department of Environment and EnergyColorado State UniversityCooperative Institute for Mesoscale Meteorological StudiesCSIROKarlsruhe Institute of TechnologyMonash UniversityNational Center for Atmospheric ResearchNational Science FoundationNorthWest Research AssociatesQueensland University of TechnologyUniversity of California San DiegoUniversity of Colorado BoulderUniversity of Illinois at Urbana-ChampaignUniversity of MelbourneUniversity of OklahomaUniversity of Washington

Groundbreaking data set gives unprecedented look at future weather

Dec. 7, 2017 | How will weather change in the future? It's been remarkably difficult to say, but researchers are now making important headway, thanks in part to a groundbreaking new data set at the National Center for Atmospheric Research (NCAR).Scientists know that a warmer and wetter atmosphere will lead to major changes in our weather. But pinning down exactly how weather — such as thunderstorms, midwinter cold snaps, hurricanes, and mountain snowstorms — will evolve in the coming decades has proven a difficult challenge, constrained by the sophistication of models and the capacity of computers.Now, a rich, new data set is giving scientists an unprecedented look at the future of weather. Nicknamed CONUS 1 by its creators, the data set is enormous. To generate it, the researchers ran the NCAR-based Weather Research and Forecasting model (WRF) at an extremely high resolution (4 kilometers, or about 2.5 miles) across the entire contiguous United States (sometimes known as "CONUS") for a total of 26 simulated years: half in the current climate and half in the future climate expected if society continues on its current trajectory.The project took more than a year to run on the Yellowstone supercomputer at the NCAR-Wyoming Supercomputing Center. The result is a trove of data that allows scientists to explore in detail how today's weather would look in a warmer, wetter atmosphere.CONUS 1, which was completed last year and made easily accessible through NCAR's Research Data Archive this fall, has already spawned nearly a dozen papers that explore everything from changes in rainfall intensity to changes in mountain snowpack."This was a monumental effort that required a team of researchers with a broad range of expertise — from climate experts and meteorologists to social scientists and data specialists — and years of work," said NCAR senior scientist Roy Rasmussen, who led the project. "This is the kind of work that's difficult to do in a typical university setting but that NCAR can take on and make available to other researchers."Other principal project collaborators at NCAR are Changhai Liu and Kyoko Ikeda. A number of additional NCAR scientists lent expertise to the project, including Mike Barlage, Andrew Newman, Andreas Prein, Fei Chen, Martyn Clark, Jimy Dudhia, Trude Eidhammer, David Gochis, Ethan Gutmann, Gregory Thompson, and David Yates. Collaborators from the broader community include Liang Chen, Sopan Kurkute, and Yanping Li (University of Saskatchewan); and Aiguo Dai (SUNY Albany).Climate and weather research coming togetherClimate models and weather models have historically operated on different scales, both in time and space. Climate scientists are interested in large-scale changes that unfold over decades, and the models they've developed help them nail down long-term trends such as increasing surface temperatures, rising sea levels, and shrinking sea ice.Climate models are typically low resolution, with grid points often separated by 100 kilometers (about 60 miles). The advantage to such coarse resolution is that these models can be run globally for decades or centuries into the future with the available supercomputing resources. The downside is that they lack detail to capture features that influence local atmospheric events,  such as land surface topography, which drives mountain weather, or the small-scale circulation of warm air rising and cold air sinking that sparks a summertime thunderstorm.Weather models, on the other hand, have higher resolution, take into account atmospheric microphysics, such as cloud formation, and can simulate weather fairly realistically. It's not practical to run them for long periods of time or globally, however — supercomputers are not yet up to the task.As scientific understanding of climate change has deepened, the need has become more pressing to merge these disparate scales to gain better understanding of how global atmospheric warming will affect local weather patterns."The climate community and the weather community are really starting to come together," Rasmussen said. "At NCAR, we have both climate scientists and weather scientists, we have world-class models, and we have access to state-of-the-art supercomputing resources. This allowed us to create a data set that offers scientists a chance to start answering important questions about the influence of climate change on weather."Weather models are typically run with a much higher resolution than climate models, allowing them to more accurately capture precipitation. This figure compares the average annual precipitation from a 13-year run of the Weather Research and Forecasting (WRF) model (left) with the average annual precipitation from running the global Community Earth System Model (CESM) to simulate the climate between 1976 and 2005 (right). (©UCAR. This figure is courtesy Kyoko Ikeda. Ite is freely available for media & nonprofit use.)Today's weather in a warmer, wetter futureTo create the data set, the research team used WRF to simulate weather across the contiguous United States between 2000 and 2013. They initiated the model using a separate "reanalysis" data set constructed from observations. When compared with radar images of actual weather during that time period, the results were excellent."We weren't sure how good a job the model would do, but the climatology of real storms and the simulated storms was very similar," Rasmussen said.With confidence that WRF could accurately simulate today's weather, the scientists ran the model for a second 13-year period, using the same reanalysis data but with a few changes. Notably, the researchers increased the temperature of the background climate conditions by about 5 degrees Celsius (9 degrees Fahrenheit), the end-of-the-century temperature increase predicted by averaging 19 leading climate models under a business-as-usual greenhouse gas emissions scenario (2080–2100). They also increased the water vapor in the atmosphere by the corresponding amount, since physics dictates that a warmer atmosphere can hold more moisture.The result is a data set that examines how weather events from the recent past — including named hurricanes and other distinctive weather events — would look in our expected future climate.The data have already proven to be a rich resource for people interested in how individual types of weather will respond to climate change. Will the squall lines of intense thunderstorms that rake across the country's midsection get more intense, more frequent, and larger? (Yes, yes, and yes.) Will snowpack in the West get deeper, shallower, or disappear? (Depends on the location: The high-elevation Rockies are much less vulnerable to the warming climate than the coastal ranges.) Other scientists have already used the CONUS 1 data set to examine changes to rainfall-on-snow events, the speed of snowmelt, and more.Running the Weather Research and Forecasting (WRF) model at 4 kilometers resolution over the contiguous United States produced realistic simulations of precipitation. Above, average annual precipitation from WRF for the years 2000-2013 (left) compared to the PRISM dataset for the same period (right). PRISM is based on observations. (©UCAR. This figure is courtesy Kyoko Ikeda. Ite is freely available for media & nonprofit use.) Pinning down changes in storm trackWhile the new data set offers a unique opportunity to delve into changes in weather, it also has limitations. Importantly, it does not reflect how the warming climate might shift large-scale weather patterns, like the typical track most storms take across the United States. Because the same reanalysis data set is used to kick off both the current and future climate simulations, the large-scale weather patterns remain the same in both scenarios.To remedy this, the scientists are already working on a new simulation, nicknamed CONUS 2.Instead of using the reanalysis data set — which was built from actual observations — to kick off the modeling run of the present-day climate, the scientists will use weather extracted from a simulation by the NCAR-based Community Earth System Model (CESM).  For the future climate run, the scientists will again take the weather patterns from a CESM simulation — this time for the year 2100 — and feed the information into WRF.The finished data set, which will cover two 20-year periods, will likely take another year of supercomputing time to complete, this time on the newer and more powerful Cheyenne system at the NCAR-Wyoming Supercomputing Center. When complete, CONUS 2 will help scientists understand how expected future storm track changes will affect local weather across the country.Scientists are already eagerly awaiting the data from the new runs, which could start in early 2018. But even that data set will have limitations. One of the greatest may be that it will rely on a single run from CESM. Another NCAR-based project ran the model 40 times from 1920 to 2100 with only minor changes to the model's starting conditions, showing researchers how the natural chaos of the atmosphere can cause the climate to look quite different from simulation to simulation.Still, a single run of CESM will let scientists make comparisons between CONUS 1 and CONUS 2, allowing them to pinpoint possible storm track changes in local weather. And CONUS 2 can also be compared to other efforts that downscale global simulations to study how regional areas will be affected by climate change, providing insight into the pros and cons of different research approaches."This is a new way to look at climate change that allows you to examine the phenomenology of weather and answer the question, 'What will today's weather look like in a future climate?'" Rasmussen said. "This is the kind of detailed, realistic information that water managers, city planners, farmers, and others can understand and helps them plan for the future."Get the dataHigh Resolution WRF Simulations of the Current and Future Climate of North America, DOI: 10.5065/D6V40SXPStudies that relied on the CONUS data setExtreme downpours could increase fivefold across parts of the U.S.Slower snowmelt in a warming worldNorth American storm clusters could produce 80 percent more rainWriter/contact:Laura Snider, Senior Science Writer

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