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Research in CGD

Recent Publications

• 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]

• 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]

• 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: 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

Climate change and other factors are drying up many of the world's rivers.
Many of the world's big rivers are drying out, with no sign of relief. Kevin Trenberth of the National Center for Atmospheric Research and his colleagues analyzed 925 rivers around the globe, from 1948 to 2004. Trenberth says a third of these rivers showed significant changes in annual flow into the ocean. And the majority of those that changed have gotten drier. [radio interview] [related]

Community Ice Sheet Model Will Aid Understanding of Sea Level Rise
Recently, scientists modified the Community Land Model (CLM), a component of CCSM, to compute ice sheet surface mass balance - the net accumulation of snow minus melting or evaporation. But to obtain a full picture on ice sheet behavior, they must pair information on surface mass balance with estimates of dynamic changes in ice flow.
[highlight] [CCSM] [CISM] [CLM] [GLIMMER]

Projecting Emperor Penguin Population in a Warming World
"Information from climate models is more reliable on larger spatial and longer temporal scales because of the natural variability that occurs from year-to-year." explains Marika Holland, a co-author of the penguin population study. [highlight] [article] [CCSM]

CGD in the News

Emissions Linked to End of 2,000-Year Arctic Trend
Staff: [story] [press release] [study] [related] [related]

Sun's Cycle Alters Earth's Climate
Staff: Gerald Meehl [story] [press release] [study]

Panelists at McCain-Udall hearing detail state's grim climate future
Staff: David Schimel [story] [related]

Rising acidity erodes Alaska's fisheries
Staff: Joanie Kleypas [story]

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