Research in CGD

Recent Publications

  • Investigating the climate impacts of global land cover change in the community climate system model.

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    Staff Author: P. Lawrence

    To further contribute to the understanding of the possible climatic impacts of anthropogenic land cover change, we have performed a series of land cover change experiments with the community land model (CLM) within the community climate system model (CCSM). To do this we have developed a new set of potential vegetation land surface parameters to represent land cover change in CLM. [article]

  • Mitigation implications of midcentury targets that preserve long-term climate policy options.

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    Staff Author: B. O'Neill

    Midcentury targets have been proposed as a guide to climate change policy that can link long-term goals to shorter-term actions. However no explicit mitigation analyses have been carried out of the relationship between midcentury conditions and longer-term outcomes. [article]

  • Influence of Bering Strait flow and North Atlantic circulation on glacial sea-level changes.

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    Staff Authors: A. Hu, G. Meehl, B.L. Otto-Bliesner, and N. Rosenbloom

    Sea-level fluctuations of about 20-30m occurred throughout the last glacial period. These fluctuations seem to have been derived primarily from changes in the volume of Northern Hemisphere ice sheets and cannot be attributed solely to ice melt caused by varying solar radiation. [article]

  • Simulation of present day and 21st century energy budgets of the southern oceans.

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    Staff Authors: K. Trenberth and J. Fasullo

    The energy budget of the modern-day southern hemisphere is poorly simulated in both state-of-the-art reanalyses and coupled global climate models. The ocean-dominated southern hemisphere has low surface reflectivity and therefore its albedo is particularly sensitive to cloud cover. [article]

  • Cloud influence on and response to seasonal Arctic sea ice loss.

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    Staff Authors: J. Kay and A. Gettelman

    Recent declines in Arctic sea ice extent provide new opportunities to assess cloud influence on and response to seasonal sea ice loss. This study combines unique satellite observations with complementary data sets to document Arctic cloud and atmospheric structure during summer and early fall. [article]

  • Evaluating Global Warming Potentials with historical temperature.

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    Staff Author: B. O'Neill

    Global Warming Potentials (GWPs) are evaluated with historical temperature by applying them to convert historical CH4 and N2O emissions to equivalent CO2 emissions. Our GWP analysis is based on an inverse estimation using the Aggregated Carbon Cycle, Atmospheric Chemistry, and Climate Model (ACC2). [article]

  • Analysis of Convective Transport and Parameter Sensitivity in a Single Column Version of the Goddard Earth Observation System, Version 5, General Circulation Model.

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    Staff Author: J. Bacmeister

    Convection strongly influences the distribution of atmospheric trace gases. General circulation models (GCMs) use convective mass fluxes calculated by parameterizations to transport gases, but the results are difficult to compare with trace gas observations because of differences in scale. [article]

  • Recent warming reverses long-term Arctic cooling.

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    Staff Authors: Caspar Ammann, Bette Otto-Bliesner and Dave Schneider

    The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60°N covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. [article]

  • Amplifying the Pacific Climate System Response to a Small 11-Year Solar Cycle Forcing.

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    Staff Authors: Gerald Meehl and Julie Arblaster

    One of the mysteries regarding Earth's climate system response to variations in solar output is how the relatively small fluctuations of the 11-year solar cycle can produce the magnitude of the observed climate signals in the tropical Pacific associated with such solar variability. [article]

  • The connection between Labrador Sea buoyancy loss, deep western boundary current strength, and Gulf Stream path in an ocean circulation model.

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    Staff Authors: Markus Jochum and Steve Yeager

    The sensitivity of the North Atlantic gyre circulation to high latitude buoyancy forcing is explored in a global, non-eddy resolving ocean general circulation model. [article]

  • Transient Simulation of Last Deglaciation with a New Mechanism for Bølling-Allerød Warming.

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    Staff Authors: B. Otto-Bliesner E. Brady, and R. Tomas

    We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Bølling-Allerød (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. [article] [abstract]

  • Cloud ice: A climate model challenge with signs and expectations of progress.

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    Staff Author: J. Bacmeister

    Present-day shortcomings in the representation of upper tropospheric ice clouds in general circulation models (GCMs) lead to errors in weather and climate forecasts as well as account for a source of uncertainty in climate change projections. [article]

  • Variations in the three dimensional structure of the atmospheric circulation with different flavors of El Niño.

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    Staff Author: K. Trenberth

    Two rather different flavors of El Niño are revealed when the full three-dimensional spatial structure of the temperature field and atmospheric circulation monthly mean anomalies is analyzed using the Japanese Reanalysis (JRA-25) temperatures from 1979 through 2004 for a core region of the tropics from 30°N to 30°S, with results projected globally onto various other fields. [article] [abstract]

  • A lagged warm event-like response to peaks in solar forcing in the Pacific region.

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    Staff Authors: G. Meehl and J. Arblaster

    The forced response coincident with peaks in the 11 year decadal solar oscillation (DSO) has been shown to resemble a cold event or La Niña-like pattern during DJF in the Pacific region in observations and two global coupled climate models. [article, early online release] [abstract]

  • Decadal Prediction: Can it be skillful?

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    Staff Authors: G. Danabasoglu and G. Meehl

    A new field called "decadal prediction" will use initialized climate models to produce time-evolving predictions of regional climate that will bridge ENSO forecasting and future climate change projections. [article, early online release] [abstract]

  • Sensitivity of CFC-11 uptake to physical initial conditions and interannually varying surface forcing in a global ocean model.

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    Staff Authors: G. Danabasoglu, K. Lindsay and S. Peacock

    Sensitivity of the oceanic chlorofluorocarbon CFC-11 uptake to physical initial conditions and surface dynamical forcing (heat and salt fluxes and wind stress) is investigated in a global ocean model used in climate studies. Two different initial conditions are used. [article] [abstract]

  • Evaluation of Forecasted Southeast Pacific Stratocumulus in the NCAR, GFDL and ECMWF Models.

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    Staff Authors: C. Hannay, J. Kiehl and D. Williamson

    We examine forecasts of Southeast Pacific stratocumulus at 20°S and 85°W during the East Pacific Investigation of Climate (EPIC) cruise of October 2001 with the ECMWF model, GFDL's AM , NCAR's CAM, and the CAM-UW (with a revised atmospheric boundary layer formulation). [article, early online release] [abstract]

  • Improving Oceanic Overflow Representation in Climate Models: The Gravity Current Entrainment Climate Process Team.

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    Staff Authors: B. Briegleb, G. Danabasoglu and W. Large

    Oceanic overflows are bottom-trapped density currents originating in semienclosed basins, such as the Nordic seas, or on continental shelves, such as the Antarctic shelf. Overflows are the source of most of the abyssal waters, and therefore play an important role in the large-scale ocean circulation, forming a component of the sinking branch of the thermohaline circulation. [article] [abstract]

  • Transient response of the MOC and climate to potential melting of the Greenland Ice Sheet in the 21st century.

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    Staff Authors: A. Hu and G. Meehl

    The potential effects of Greenland Ice Sheet (GrIS) melting on the Atlantic meridional overturning circulation (MOC) and global climate in the 21st century are assessed using the Community Climate System Model version 3 with prescribed rates of GrIS melting. [article] [abstract]

  • "Modes of Variability" and Climate Change.

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    Staff Author: G. Branstator

    A 62-member ensemble of coupled general circulation model (GCM) simulations of the years 1940-2080, including the effects of projected greenhouse gas increases, is examined. The focus is on the interplay between the trend in the Northern Hemisphere December-February (DJF) mean state and the intrinsic modes of variability of the model atmosphere. [article] [abstract]

  • Impact of latitudinal variations in vertical diffusivity on climate simulators.

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    Staff Author: M. Jochum

    The currently available theoretical and observational evidence for a latitudinal structure of thermocline vertical diffusivity is synthesized and included in a state of the art coupled climate model. [article] [abstract]

  • Examining the Interaction of Growing Crops with Local Climate Using a Coupled Crop-Climate Model.

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    Staff Author: D. Lawrence

    Crop impact assessments currently use climate model output offline to drive process-based crop models. However, in regions where local climate is sensitive to land surface conditions more consistent assessments may be produced with the crop model embedded within the land surface scheme of the climate model. [article] [abstract]

  • Comparisons of satellites liquid water estimates to ECMWF and GMAO analyses, 20th century IPCC AR4 climate simulations, and GCM simulations.

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    Staff Author: J. Bacmeister

    To assess the fidelity of general circulation models (GCMs) in simulating cloud liquid water, liquid water path (LWP) retrievals from several satellites with passive sensors and the vertically-resolved liquid water content (LWC) from the CloudSat are used. [article]

  • Changes in Continental Freshwater Discharge from 1948-2004.

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    Staff Authors: A. Dai, T. Qian, and K. Trenberth

    A new data set of historical monthly streamflow at the farthest downstream stations for world's 925 largest ocean-reaching rivers has been created for community use. Available new gauge records are added to a network of gauges that covers ~80 × 106 km2 or ~80% of global ocean-draining land areas and accounts for about 73% of global total runoff. [article, early online release] [abstract]

  • Equilibrium Climate Sensitivity: Is It Accurate to Use a Slab Ocean Model?

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    Staff Authors: G. Danabasoglu and P. Gent

    The equilibrium climate sensitivity of a climate model is usually defined as the globally averaged equilibrium surface temperature response to a doubling of carbon dioxide. This is virtually always estimated in a version with a slab model for the upper ocean. The question is whether this estimate is accurate for the full climate model version, which includes a full-depth ocean component. [article] [abstract]

  • How much climate change can be avoided by mitigation?

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    Staff Authors: W. Washington, G. Meehl, H. Teng, C. Tebaldi, D. Lawrence, L. Buja and W. Strand

    Avoiding the most serious climate change impacts will require informed policy decisions. This in turn will require information regarding the reduction of greenhouse gas emissions required to stabilize climate in a state not too much warmer than today. [article] [abstract]

  • Spatiotemporal patterns of changes in maximum and minimum temperatures in multi-model simulations.

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    Staff Author: A. Dai

    This paper analyzes and attributes spatial and temporal patterns of changes in the diurnal cycle of land surface air temperature in 20 simulations from 11 global coupled atmosphere-ocean general circulation models during the 20th century and the 21st century under the SRES A1B scenario. [abstract] [article]

  • Decadal Climate Prediction: Opportunities and Challenges.

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    Staff Authors: J. Hurrell, G. Danabasoglu, G. Meehl, K. Trenberth & J. Tribbia

    The scientific understanding of Earth's climate system is now sufficiently developed to show that climate change from anthropogenic greenhouse gas forcing is already upon us, and the rate of change as projected exceeds anything seen in nature in the past 10,000 years. Uncertainties remain, however, especially regarding how climate will change at regional and local scales. [article]

  • North Pacific Climate Response to Freshwater Forcing in the Subarctic North Atlantic: Oceanic and Atmospheric Pathways.

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    Staff Authors: C. Deser and A. Hu

    Sudden changes of the Atlantic meridional overturning circulation (AMOC) are believed to have caused large, abrupt climate changes over many parts of the globe during the last glacial and deglacial period. [article] [abstract]

  • Global warming due to increasing absorbed solar radiation.

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    Staff Authors: K. Trenberth and J. Fasullo

    Global climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are examined for the top-of-atmosphere radiation changes as carbon dioxide and other greenhouse gases build up from 1950 to 2100. [article] [abstract]

  • The contribution of snow condition trends to future ground climate.

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    Staff Author: D. Lawrence

    Global climate models predict that terrestrial northern high-latitude snow conditions will change substantially over the twenty-first century. Using the Community Land Model, we isolate how trends in snowfall, snow depth, and snow-season length affect soil temperature trends. [article] [abstract]

  • Coordinated Ocean-ice Reference Experiments (COREs).

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    Staff Authors: F. Bryan, G. Danabasoglu, W. Large and S. Yeager

    Coordinated Ocean-ice Reference Experiments (COREs) are presented as a tool to explore the behaviour of global ocean-ice models under forcing from a common atmospheric dataset. We highlight issues arising when designing coupled global ocean and sea ice experiments, such as difficulties formulating a consistent forcing methodology and experimental protocol. [article] [abstract]

  • Earth's Global Energy Budget.

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    Staff Authors: K. Trenberth, J. Fasullo and J. Kiehl

    An update of the Earth's global annual mean energy budget is given in the light of new observations and analyses. Changes over time and contributions from the land and ocean domains are also detailed. [article]

  • A comparison of PMIP2 model simulations and the MARGO proxy reconstruction...

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    Staff Authors: B. Otto-Bliesner and E. Brady

    Results from multiple model simulations are used to understand the tropical sea surface temperature (SST) response to the reduced greenhouse gas concentrations and large continental ice sheets of the last glacial maximum (LGM). [article] [abstract]

  • A regional perspective on trends in continental evaporation.

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    Staff Author: C. Ammann

    Climate models suggest that enhanced greenhouse gas concentrations and aerosols have major impacts on the land energy and water cycles, and in particular on evapotranspiration (ET). We analyze how the main external drivers of ET vary regionally, using recent data FLUXNET and GSWP-2. [article] [abstract]

  • Cause of the widening of the tropical belt since 1958.

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    Staff Authors: C. Deser and J. Lu

    Previous studies have shown that the width of the tropical belt has been increasing since at least the late 1970s based on a variety of metrics. One such metric, the frequency of occurrence of a high-altitude tropopause characteristic of the tropics, is used here... [article] [abstract]

  • Differences in the Indonesian seaway in a coupled climate model and their relevance to Pliocene climate and El Niño.

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    Staff Authors: M. Jochum and C. Shields

    A fully coupled general circulation model is used to investigate the hypothesis that during Pliocene times tectonic changes in the Indonesian seas modified the Indo-Pacific heat transport and thus increased the zonal sea surface temperature gradient in the equatorial Pacific to its large, current magnitude. [article]

  • The computational future for climate and Earth system models: on the path to petaflop and beyond.

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    Staff Authors: W. Washington, L. Buja and A. Craig

    The development of the climate and Earth system models has had a long history, starting with the building of individual atmospheric, ocean, sea ice, land vegetation, biogeochemical, glacial and ecological model components. [abstract]

  • Atmospheric Circulation Trends, 1950-2000:

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    The Relative Roles of Sea Surface Temperature Forcing and Direct Atmospheric Radiative Forcing

    Staff Authors: C. Deser and A. Phillips

    The relative roles of direct atmospheric radiative forcing and observed sea surface temperature forcing of global December-February atmospheric circulation trends during the second half of the twentieth century are investigated using CAM3 experiments. [article] [abstract]

  • Predicting 21st-century polar bear habitat distribution from global climate models.

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    Staff Authors: M. Holland and D. Bailey

    Projections of polar bear (Ursus maritimus) sea ice habitat distribution in the polar basin during the 21st century were developed to understand the consequences of anticipated sea ice reductions on polar bear populations. [article] [abstract]

  • Demographic models and IPCC climate projections predict the decline of an emperor penguin population.

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    Staff Author: M. Holland

    Studies have reported important effects of recent climate change on Antarctic species, but there has been to our knowledge no attempt to explicitly link those results to forecasted population responses to climate change. [article] [abstract]

  • Effect of the Atlantic hurricanes on the oceanic meridional overturning circulation and heat transport.

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    Staff Authors: A. Hu and G. Meehl

    Hurricanes have traditionally been perceived as intense but relatively small scale phenomena, with little effect on the large scale climate system. However, recent evidence has suggested that hurricanes could play a much more significant role in global climate. [article] [abstract]

  • A new sea surface temperature & sea ice boundary data set for CAM.

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    Staff Authors: J. Hurrell, J. Hack, D. Shea, and J. Caron

    A new surface boundary forcing dataset for uncoupled simulations with the Community Atmosphere Model is described. It is a merged product based on the monthly mean Hadley Centre sea ice and SST dataset version 1 (HadISST1) and version 2 of the National Oceanic and Atmospheric Administration (NOAA) weekly optimum interpolation (OI) SST analysis.[article]

  • The Mid-1970s Climate Shift in the Pacific and the Relative Roles of Forced versus Inherent Decadal Variability.

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    Staff Authors: A. Hu and G. Meehl

    A significant shift from cooler to warmer tropical Pacific sea surface temperatures (SSTs), part of a pattern of basinwide SST anomalies involved with a transition to the positive phase of the Interdecadal Pacific Oscillation (IPO), occurred in the mid-1970s with effects that extended globally. [article] [abstract]

  • Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss.

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    Staff Authors: D. Lawrence, R. Tomas, M. Holland and C. Deser

    Coupled climate models and recent observational evidence suggest that Arctic sea ice may undergo abrupt periods of loss during the next fifty years. Here, we evaluate how rapid sea ice loss affects terrestrial Arctic climate and ground thermal state in the Community Climate System Model. [article] [abstract]

  • Virtual Field Campaigns on Deep Tropical Convection in Climate Models.

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    Staff Author: J. Bacmeister and C. Hannay

    High-resolution time-height data over warm tropical oceans are examined, from three global atmosphere models [GFDL's AM2, NCAR's CAM3, and a NASA GMAO model], field campaign observations, and observation-driven cloud model outputs. [abstract] [article]

Research Highlights

The hydrologic link between land use changes and climate. A new study led by NCAR scientist Peter Lawrence has found that impacts to Earth's hydrological cycle - not changes in the reflection or absorption of solar radiation - are the most important driving force in how human-caused land use changes affect climate. The findings contradict previous research and suggest that land cleared of forest for agriculture could have a greater warming impact on regional temperatures than previously thought. Staff: Peter Lawrence [highlight] [paper] [TSS]

Through the past, meticulously. In a bright, quiet, air-conditioned room in eastern Tennessee, a portrait of Earth's progression from ice age to present is taking shape in unprecedented detail. Each day, up to 100 years of climatic history unfolds. By early this year, the story will be complete, thanks to some five million processing hours on two successive supercomputers at the U.S. Department of Energy (DOE) Oak Ridge National Laboratory. Staff: Bette Otto-Bliesner [highlight] [CCR]

What's With This Weather? Brrr: The AO is way low. No matter how you slice it, the last few weeks have been consistently wintry across large chunks of North America and Eurasia. "Most winters are not dominated by any particular regime," note Hurrell and Deser in a recent overview of the NAO for the Journal of Marine Systems. In other words, February could flip into a positive NAM mode just as easily as it could stay largely negative. Staff: Clara Deser and James Hurrell. [highlight] [study] [related] [CAS]

The Arctic heats up. The Arctic is on thin ice-literally as well as figuratively. New research shows that temperatures were warmer there in the 1990s than any decade in at least 2,000 years. Arctic sea ice has been dwindling for the past few decades, with 2009 levels well below normal. Greenland's melting ice sheets have the potential to dramatically raise sea levels, and thawing permafrost threatens to release massive amounts of methane into the atmosphere. [highlight] [CCSM] [OCE]

Upcoming Events

CGD Seminar
Speaker: Amy Clement, University of Miami
Topic: Low Clouds and Climate Change
Date/Time: 19 February 2010, 3:30 pm
Location: NCAR Mesa Lab, Main Seminar Room [abstract] [schedule] [seminar info]