ClimateStudyGroup

The IGPP Climate Study Group

The primary purpose of the Study Group is to provide a forum for scientists across the lab to exchange ideas and form new collaborations. The presentations are meant to be broad enough to engage the wide cross-section of scientists interested in climate change and its impacts.

The group presentations will focus on the following topics: climate change science, linkages between climate change and energy security, and linkages between climate change and socio-economic impacts. The presenters will be a mix of LANL scientists and invited guests.

A list of previous presentations (some of which include a pdf of the presentation) are available at the bottom of this page.

If you are interested in giving a presentation or would like more information about the series, please contact Todd Ringler or Gary Geernaert.

Upcoming Seminars

No seminars scheduled at this time.

Previous Seminars (Some presentations are available online.)

December 1, 2008, 10 AM

A new nonhydrostatic atmospheric model based on a hybrid vertical coordinate

Michael Toy, Department of Atmospheric Science, Colorado State University

Location: CNLS Conference Room

The isentropic system of equations has particular advantages in the numerical modeling of weather and climate. These include the elimination of the vertical velocity in adiabatic flow, which simplifies the motion to a two-dimensional problem and greatly reduces the numerical errors associated with vertical advection. Vertical resolution is enhanced in regions of high static stability which leads to better resolving of features such as the tropopause boundary. Also, sharp horizontal gradients of atmospheric properties found along frontal boundaries in traditional Eulerian coordinate systems are nonexistent in the isentropic coordinate framework.

The extreme isentropic overturning that can occur in fine-scale atmospheric motion presents a challenge to nonhydrostatic modeling with the isentropic vertical coordinate. A new nonhydrostatic atmospheric model based on a generalized vertical coordinate is presented here. The coordinate is specified in a similar manner as Konor and Arakawa, but elements of arbitrary Eulerian-Lagrangian methods are added to provide the flexibility to maintain coordinate monotonicity in regions of negative static stability and return the coordinate levels to their isentropic targets in statically stable regions. The model is mass-conserving and implements a vertical differencing scheme that satisfies two additional integral constraints for the limiting case of z coordinates.

The hybrid vertical coordinate model is tested with mountain wave experiments which include a downslope windstorm with breaking gravity waves. The results show that the advantages of the isentropic coordinate are realized in the model with regards to vertical tracer and momentum transport. Also, the isentropic overturning associated with the wave breaking is successfully handled by the coordinate formulation.

November 24, 2008, 11 AM

Arctic warming, rapid sea ice loss, and snow state changes: Influence on projected near-surface permafrost degradation

David Lawrence, National Center from Atmospheric Research

Location: Quantum Room (Bldg 40 , rm N101)

Projected climatic changes in the Arctic associated with increasing greenhouse gas concentrations are varied. Global climate models suggest that warming in the Arctic will be considerably stronger than the rest of the world. In the Community Climate System Model (CCSM3), 21st century terrestrial Arctic warming ranges from ~+4 to +8°C depending on emission scenario. This warming is non-linear, due in part, to periods of accelerated sea ice loss. Along with the warming, CCSM3 (and other global models) project an increase in winter snowfall and concomitant changes in snow depth, snow density, and snow-season length. Here, we evaluate the roles of Arctic warming, accelerated sea ice loss, and snow state changes on the rate and extent of soil warming and permafrost degradation. We utilize the Community Land Model (CLM) with improved permafrost dynamics to evaluate and compare the large-scale near-surface permafrost response to these climatic forcings. The strong projected warming is, not surprisingly the biggest contributor to permafrost degradation. However, we can attribute roughly 18% of the permafrost degradation to increasing snowfall and the resulting maintenance of the insulating snowpack even in the face of strong warming. We also find that a period of accelerated warming associated with rapid sea ice loss can accelerate soil warming and lead to rapid thaw of warmer permafrost and to increased vulnerability of colder permafrost.

November 13, 2008, 1 PM

The development of a second generation Global Dynamic Global Vegetation Model: New tools for constraining the terrestrial climate-carbon cycle feedback.

Rosie Fisher, University of Sheffield

Location: CNLS Conference Room

The magnitude of the feedback between the terrestrial biosphere and the atmosphere represents a large uncertainty in climate predictions. Recent model inter-comparisons indicate that choice of Dynamic Global Vegetation Model (DGVM) alone can change the size of the climate-carbon cycle feedback such that the 2100 atmospheric CO2 concentration varies by as much as 227ppm. Existing DGVMs are skilled at simulating the contemporary carbon cycle, but differ significantly in their responses future climate and CO2 concentrations. To move on from this situation, we must intensify our efforts to interface existing ecological data and experiments with model construction and parameterisation. However this is not straightforward using existing DGVMs, as these typically require many parameters which are not easily linked to observations. I will discuss the development of a new DGVM based on the 'Ecosystem Demography' (ED) approach. Using the individual tree based ED allows for the first time, in a global context, the simulation of vertical competition for light between plant types, heterogeneity of the land surface resulting from disturbance and ultimately the mechanistic representation of timescales determining the velocity of biome shifts. This new 'second generation' DGVM, which is coupled to the land surface exchange scheme of the Hadley Centre family of climate models, is parameterised using observational data and as such represents a major shift in capacity for integration of ecological understanding into climate-relevant vegetation modelling.

November 10, 2008, 1 PM

Examining the effects of horizontal resolution on regional climate model simulations using a multi-model ensemble.

Sara Rauscher, Earth System Physics Section, The Abdus Salam International Centre for Theoretical Physic, Trieste, Italy

Location: CNLS Conference Room

High resolution climate information is needed for adaptation to and mitigation of the impacts of climate change and variability at a range of time scales. For both regional and global climate models (RCMs and GCMs), there is a general perception that increased horizontal resolution can improve the simulation of regional climate features. However, there have been relatively few systematic investigations of the sensitivity of climate model simulations to horizontal resolution. Here we make use of a unique multi-model ensemble produced by the European ENSEMBLES project. Participating institutions performed two reanalysis-driven RCM simulations at 50 km and 25 km grid spacings over a large European domain. In all other respects (e.g., lateral boundary conditions, common minimum domain, parameterization settings) the model simulations are the same at the two resolutions, thus providing an opportunity to assess resolution effects on RCM simulations. We focus on precipitation, likely the most sensitive variable to model resolution. A comparison of the seasonal spatial and temporal mean and variability of the modeled precipitation with high-resolution gridded climate data shows improvements at higher resolution for the summer season in most e regions, while the opposite is true in winter. Application of the Kolmogorov-Smirnov test indicates that the distributions of the 25 km and 50 km simulated daily precipitation are significantly different over most land areas, especially over areas of high topography. This difference is due to a better simulation of rainy day frequency and intensity at 25 km. Overall the results indicate that higher resolution yields improvements in some areas and in some seasons, but improved performance is not universal, indicating that increased resolution alone does not necessarily result in better simulations.

May 13, 2008, 12 Noon

Pictures of a Problematic Arctic: Pristine or Polluted, Prescriptive or Predictive

Manvendra K. Dubey (EES-6) and Claudio Mazzoleni (ISR-2)

Location: CNLS Conference Room

The Arctic is a beacon of global change. Recent observational trends show a rapid melt-ing of the Arctic ice sheets, with the possibility of an ice-free Arctic within our lifetime. This would abruptly tip our planet to a new climate state with extreme impacts. The Arc-tic has warmed twice as fast as the global mean in the last century, and the anthropogenic greenhouse gas forcing only accounts for about half of the observed Arctic warming. The Arctic vortex serves as an atmospheric receptor of air pollution from northern mid-latitude continental areas, as manifested by the thick aerosol layers. This Arctic Haze is a regular regional winter and springtime feature. Emission sources that contribute to it include anthropogenic black carbon (BC) and sulfate, smoke from massive boreal fires and dust from desert regions. These regional haze perturbations trigger unique regional responses, such the darkening of ice by deposition of BC, which promotes the melting of ice sheets. However, there are substantial uncertainties in our ability to quantify and pre-dict these regional Arctic forcing and impacts.

The 4th International Polar Year (IPY, April '07-08) just culminated with a concerted campaign of intense international research to gain new knowledge about Earth's polar regions, how those regions are changing, and how such changes are impacting the health of our planet. In April 2008 about 275 scientists from DOE, NASA, NOAA, and Europe converged in Alaska with 6 research aircrafts to perform the most comprehensive measurements of the polar environment: radiation, chemistry, aerosols, clouds and ice. Air-borne measurements were complemented by space-based measurements from the NASA-A Train satellite sensors.

Los Alamos deployed the world's first 3-laser photoacoustic instrument, which measures aerosol absorption and scattering at 405, 532 and 781 nm in situ for DOE's Indirect and Semidirect Effects of Aerosols (ISDAC) campaign (www.arm.gov). There were 42 complementary measurements of cloud micro-physics, aerosol chemistry, and ice composition (Our DOE instruments were deployed on a CONVAIR-580 aircraft operated by NRC Canada. We will share the excitement and collaborative spirit of the campaign. We will provide snapshots of the region and provide first blush glimpses of our results. We will share the breathtaking beauty of the Arctic region and signatures of anthropogenic perturbations using pictures taken during our field campaign. We intercepted intense pollu-tion from carbon from Siberian fires, Chinese dust and sulfate Eurasian energy production. Dubey has been asked to present ISDAC preliminary findings of the DOE-team this June at the GEWEX Cloud System Study meeting in Toulouse. IPY-2008 is an opportu-nity to educate and excite the public and help train the next generation of scientists, leaders, and educators. It is also an opportunity to link LANL expertise in ice modeling, in situ aerosol-ice measurements and remote sensing to strengthen LAN's contributions to our emerging energy security mission. This talk is aimed to excite and engage the climate researchers to catalyze this integration at LANL.

February 13, 2008, 12 Noon

Feedbacks between atmospheric moist convection and surface processes in semi-arid regions

J. Galewsky
Department of Earth and Planetary Sciences, University of New Mexico, Albuqueruqe, NM

Location: CNLS Conference Room

In a classic 1951 paper, Luna Leopold showed that the ratio of rainfall extrema to rainfall averages increases as the climate becomes more arid. This line of thinking has influenced much geomorphology research, but the basic meteorological mechanisms involved remain unknown. The potential for drought to increase both precipitation intensity and slope erodibility, which further decreases soil and vegetation cover, suggests the potential for previously unrecognized feedbacks between climate and landscape dynamics in semi-arid regions. We have used an idealized version of an atmospheric model to explore this phenomenon, and preliminary results show that the precipitation variability (defined here as the average of the 90th percentile of hourly rainfall rates divided by the average hourly rainfall rate) increases with the Bowen Ratio (ratio of sensible to latent heat fluxes) and is thus consistent with Leopold (1951). This modeling approach may therefore provide a useful framework for understanding how continental convection changes as a function of land surface state. The modeling framework is similar to that used for studies of oceanic radiative-convective equilibrium (e.g. Tompkins and Craig, 1998) but uses a land surface parameterization with a fixed moisture availability instead of an oceanic surface. The model is run for approximately 30 days until an equilibrium is established between radiative cooling and convective heating in the atmosphere. By varying the moisture availability, a range of climate states are accessible, ranging from humid (low Bowen Ratio) to arid (high Bowen Ratio) conditions. By carefully diagnosing the model output fields, we can gain substantial insight into the links between land surface conditions and convective precipitation.

February 4, 2008, 10 AM

The Sun, the Moon, and Central America

Robert F. Cahalan
Head of Climate & Radiation Branch,
NASA Goddard Space Flight Center

Location: CNLS Conference Room

On January 25, 2003, the Solar Radiation and Climate Experiment, SORCE, was launched from Cape Kennedy, and for 5 years 4 instruments onboard have been monitoring variations in the Sun's spectral and total irradiances (TSI and SSI) with high precision. I summarize what we’ve been learning of solar variability. Examples range over wavelengths from 1 to 2400 nanometers, and over timescales from minutes (solar flares) to years. For the Sun's total irradiance, or TSI, a comparison of SORCE results to the ACRIM series begun in 1980 shows improvements in knowledge of the absolute value of TSI, and its 11-year cycle of magnetic activity, but it also raises a conundrum: How might the Sun have changed since pre-industrial times, indeed since Galileo first observed sunspots and determined the Sun's rotation period, in 1610? The answer is crucial for distinguishing that part of global warming due to human activity, from that due to natural variability, since the principal external climate driver is the Sun. I show that the Moon holds the answer to this climate conundrum, since the pre-industrial solar scenarios used by IPCC can be distinguished using a high precision measurement of the temperature profile of the upper 10 meters of lunar regolith. The Lunar Borehole experiment would be a fitting follow-on to the legacy of Apollo's initial Heat Flux Experiment. Finally, changing our focus from the Sun and Moon to Central America, I describe recent field measurements and outreach activities in which the speaker was involved as a U.S. State Department "Embassy Science Fellow" during 2007. This work relates to NASA's Google partnership, to the NASA SERVIR project, to the July- August 2007 NASA TC4 field campaign, and to the international Group on Earth Observations, or GEO. GEO and related collaborative efforts will need to be intensified if society is to take optimal advantage of our Earth observations to manage resources and adapt to climate change.

December 17, 2007, 3 PM

Mostly Settled Science of Anthropogenic Influence on Earth's Climate
Chick Keller
Location: Physics Auditorium

"We are 90% confident that most of the warming in the past 50 years is due to humans." 4AR Policy Makers Summary. With the recent publication of the Fourth Assessment Report of the United Nations' Intergovernmental Panel on Climate Change (Working Group 1) there has been renewed interest and controversy about how certain the scientific community is of its conclusions: that humans are influencing the climate and that global temperatures will continue to rise rapidly in this century. This presentation attempts to update what is known and in particular what advances have been made in the past 5 years or so. It does not attempt to be comprehensive. Rather it focuses on the most controversial issues, which are actually few in number. They are:

o Is the surface temperature record accurate or is it biased by heat from cities, etc?
o Is that record significantly different from past warmings such as the Medieval Warming Period?
o Is not the sun's increasing activity the cause of most of the warming?
o Can we model climate and predict its future, or is it just too complex and chaotic?
o Are there any other changes in climate other than warming, and can they be attributed to the warming?

Finally there is a very brief discussion of the societal policy response to the scientific message.Despite continued uncertainties, the review finds an affirmative answer to these questions. Of particular interest are advances that seem to explain why satellites don't see as much warming as surface instruments, how we are getting a good idea of recent paleoclimates, and why the 20th century temperature record was so complex. It makes the point that in each area new information could come to light that would change our thinking on the quantitative magnitude and timing of anthropogenic warming, but it is unlikely to alter the basic conclusions.

November 20, 2007, 2 PM

ESSENCE: Ensemble Simulations of Extreme Weather Events under Nonlinear Climate Change
Henk Dijkstra, Professor of Dynamical Oceanography, Utrecht University
Center for Nonlinear Studies Conference Room (TA 3, 1690)

The ESSENCE project, carried out within the Distributed European Infrastructure for Supercomputing Applications (DEISA), aims at a better understanding of forced and internally generated climate variability. A relatively large (17 member) ensemble simulation of climate change in response to the SRES-1b scenario (over the period 1950-2100) has been carried out using the ECHAM5-OM1 (MPI) model. This standard ensemble is accompanied by a set of 4 experimental ensembles that address the effect of parameter sensitivities. In this presentation an overview of the project will be given and results from (i) the standard ensemble, focussing on the forced signal versus internal variability, and (ii) the special ensembles, in particular the ensemble where a collapse in the Atlantic meridional overturning is simulated, are presented. Focus will be on the changes in statistics of extreme events in temperature, precipitation and wind over Western Europe and the physical processes responsible for these changes.

November 8, 2007, 11 AM

Climate change over two mid-Pleistocene glacial cycles in the Valles Caldera, New Mexico
Peter Fawcett, University of New Mexico
Center for Nonlinear Studies Conference Room

A long-lived middle Pleistocene lake formed in the Valle Grande, a large moat valley of the Valles Caldera in northern New Mexico, when a post-caldera eruption (South Mountain rhyolite) dammed the drainage out of the caldera. The deposits of this lake were cored in May 2004 (GLAD5 project, hole VC-3) and 81 m of mostly lacustrine silty mud was recovered. A tentative chronology has been established for VC-3 with a basal tephra Ar-Ar date of 552 +/- 3 kyr, a correlation of glacial terminations V and VI in the core with other long Pleistocene records (SPECMAP) and the recognition of two geomagnetic field polarity events in the core (14a and 11a) which can be correlated with globally recognized events. This record spans a critical interval of the middle Pleistocene from MIS 14 (552 kyr B.P.) to MIS 10 (~350 kyr B.P.), at which time the lacustrine sediments filled the available accommodation space in the caldera moat. Multiple analyses including core sedimentology and stratigraphy, sediment density and rock magnetic properties, organic carbon content and carbon isotopic ratios, C/N ratios, and pollen content reveal two glacial/interglacial cycles in the core (MIS 14 to MIS 10). Glacial terminations V and VI and complete sections spanning interglacials MIS 13 and MIS 11 are captured at a high resolution. In the VC-3 record, both of these interglacials are relatively long compared with the intervening glacials (MIS 14 and MIS 12), and interglacial MIS 13 is significantly muted in amplitude compared with MIS 11. These features are similar to several other mid-Pleistocene records. Of particular interest is relatively large amplitude hydrologic variability evident in the interglacial MIS 11 section. Here, prominent wet-dry cycles with a ~11 ka duration are shown by correlative changes in sedimentology (laminated vs. mudcracked horizons) and in lake productivity (organic carbon, biogenic silica). We hypothesize that this variability arises from a split-precessional cycle that modulates the strength of the southwest North American summer monsoon and hence summer rainfall amounts during this extended interglacial period. Similar periodicities are not found during the glacial periods, as the lake moisture source is dominated by westerly frontal systems and a southerly deflected polar jet stream.

September 13 , 2007 , 10 AM

Error Reduction and Convergence in Climate Prediction
Charles Jackson, University of Texas at Austin
Center for Nonlinear Studies Conference Room

Although climate models have steadily improved their ability to reproduce the observed climate, over the years there has been little change to the wide range of sensitivities exhibited by different models to a doubling of atmospheric CO2 concentrations. Stochastic optimization is used to mimic how six independent climate model development efforts might use the same atmospheric general circulation model, set of observational constraints, and model skill criteria to choose different settings for parameters thought to be important sources of uncertainty. As compared to the default model sensitivity of 2.4ºC, each optimized model improved global skill scores by a similar 7% and had nearly identical 3ºC sensitivities, but with different regional responses. The implication is that current generation models are close to a critical level of skill enabling more convergent predictions of change at the largest scales even though regional differences persist.

June 26 , 2007 , 12 Noon

An open discussion of LANL's climate strategy, Part I
Gary Geernaert, IGPP
TA-03, SM 200 (Advanced Computing Lab), CCS Conference Room, Room 116

A summary of proposed changes to the funding model used by OBER will be provided. The discussion will also explain the "Science Focus Areas" (SFAs) that will likely accompany this new model. The new model will likely also include discretionary funds held back at DOE for high impact innovative ideas from across the DOE Lab complex. This discussion will include new projects and ideas developed at LANL over the past year. Comments, suggestions, and reasearch ideas that can be used to inform and develop the LANL climate strategy are welcome. These ideas should be sent to Gary and, if possible, posted to the climate email list.

July 17, 2007 , 12 Noon

An open discussion of LANL's climate strategy, Part II
Gary Geernaert, IGPP
TA-03, SM 200 (Advanced Computing Lab), CCS Conference Room, Room 116

June 5 , 2007 , 12 Noon

Vulnerability to climate changes in the Himalaya region: A preliminary discussion of the upper Brahmaputra Basin
Li Zheng, T-7
TA-03, SM 200 (Advanced Computing Lab), CCS Conference Room, Room 116

In the talk I will provide a general overview on the existing field evidences on the warming of Himalaya region and its changing environment as well as some projected trends. I will also briefly discuss the potential impacts of climate change on the regional social-ecosystem and its global consequences. I will then use case studies from upper Brahmaputra Basin to focus on possible local impacts, and introduce our research of spatial vulnerability mapping in this context. In quantifying the vulnerability, we adopt the generic IPCC definition and formulas. I will discuss the practical and theoretical difficulties in operationalizing these formulas. I will also borrow from the adaptive cycle theory to demonstrate the necessity for expanding the scope of vulnerability assessment, and illustrate that, in order to improve system resilience and its adaptive capacity, there is a strong need for in-depth coupled social-ecosystem dynamics studies.

May 22, 2007 , 12 Noon

Physical characteristics of energy technologies and their innovation potential
Jessika Trancik, Santa Fe Institute
TA-03, SM 200 (Advanced Computing Lab), CCS Conference Room, Room 116

Innovation is critical for developing low-cost and low-carbon energy technologies to mitigate climate change. Due to the long lifetime of CO2 in the atmosphere and the projected increase in global energy demand, stabilizing CO2 atmospheric concentration at an acceptable level will become increasingly more difficult with time. In addition, because technologies tend to improve with investment, we risk becoming locked into suboptimal technologies. For these reasons we are faced with an unprecedented technological innovation challenge. This talk will focus on innovation in the energy sector from an engineering perspective. I will discuss ongoing work on how physical characteristics of technologies, such as unit scale and degrees of freedom, affect innovation rates. This work aims to address the following questions. What types of energy technologies should we invest in? How should we design energy technologies for rapid innovation?

May 8, 2007 , 12 Noon

Interactions between climate and ecosystem dynamics
Nate McDowell, EES-2
TA-03, SM 200 (Advanced Computing Lab),CCS Conference Room, Room 116

Terrestrial ecosystems play a significant role in regional and global climate. Terrestrial gross primary production is arguably the single largest flux of CO2 out of the atmosphere, a fraction of which is sequestered into biomass with the remainder released back to the atmosphere via autotrophic and heterotrophic respiration. These fluxes are an order of magnitude greater than fossil fuel emissions, and thus slight perturbations to their balance can have large impacts on atmospheric CO2. Terrestrial ecosystems are currently a "sink" for atmospheric CO2, though this sink is threatened by climate change impacts on terrestrial ecosystems. In addition, terrestrial ecosystems have a significant impact on radiative forcing (e.g. albedo), regional precipitation recycling, and are crucial to managing our water resources. In this talk I will present the state of the knowledge regarding the role of terrestrial ecosystems on climate and the impact of climate on terrestrial ecosystem structure and function. I will then describe in current activities funded by Office of Science, LDRD and IGPP that address these issues. Lastly, I will describe a path forward that may allow an increased rate of knowledge gain towards understanding and solving climate-terrestrial ecosystem impacts.

April 24, 2007, 12 Noon

Global and Greenland Climate: Past, Present, and Future
Petr Chylek, ISR-2
TA-03, SM 200 (Advanced Computing Lab), CCS Conference Room, Room 116

Using the DOE MTI (Multispectral Thermal Imager) experience and NASA MODIS (Moderate Resolution Imaging Spectroradiometer) radiances we have developed a remote sensing method to detect Greenland ice sheet melt area with a spatial resolution of 0.25 or 1 km2 (compared to 625 km2 of the current microwave method). We have obtained time series of the Greenland melt for the year 2000-2006 and found a high correlation with the average summer air temperature at nearby coastal station. Using summer air temperature as a proxy, we have reconstructed the melt area for the years 1880-2005. We found a high interannual variability with the maximum of the melt in 1930s when melt area was about 50% larger than during the first decades of this century. Using satellite retrieval of aerosol optical depth and increasing concentration of carbon dioxide we show that increasing carbon dioxide and decreasing aerosol atmospheric loading (solar brightening) contribute about equally to the current rate of global warming. From the satellite and surface observation we deduce the climate sensitivity to be 0.4 plus or minus 0.1K/Wm-2, which corresponds to global warming due to doubling of carbon dioxide of 1.6K plus or minus 0.4K. The IPCC, 2007 report (4AR) suggests the range of 1.5 to 4.5K. The reported research was done in collaboration with M. Dubey (LANL), M. McCabe (LANL), J. Dozier (UC Santa Barbara), U. Lohmann (ETH Zurich), M. Mishchenko (NASA GISS) and R. Kahn (NASA, JPL).

April 10, 2007, 12 Noon

Three-dimensional radiative transfer: What it is? & Why it matters? (.mov of WAIL)
Anthony Davis, ISR-2
TA-03, SM 200 (Advanced Computing Lab), CCS Conference Room, Room 116

I will start with a semi-technical statement of the general 3D radiative transfer problem and project onto scale-space the broad categories of radiation problems in atmospheric science that are impacted by 3D variability. This leads to very different flavors of solutions. I will then survey my current work funded by NASA's Radiation Science and DOE's Atmospheric Radiation Measurement (ARM) programs. It typically involves statistical characterization of cloud variability and modeling radiative transfer in such 3D media. However, there is also a spin-off in instrument development: the Wide-Angle Imaging Lidar (WAIL), a new concept in cloud probing from ground.

March 29, 2007, 12 Noon

Seasonal Acceleration of Inland Ice via Longitudinal Coupling to Marginal Ice
Steve Price, Bristol Glaciology Centre, University of Bristol
CNLS, Conference Room

We use an ice-flow model with appropriate physics to demonstrate that seasonal flow variations in the marginal region of an ice sheet can be transmitted upstream via longitudinal coupling. This finding suggests that previous observations of seasonal flow acceleration near the western flank of the Greenland ice sheet, which have been attributed to local changes in basal lubrication and sliding, require a broader interpretation. We demonstrate that these same observations can be explained by seasonal accelerations that are initiated up to ~12 km closer to the margin where, (1) the ice is up to 40% thinner, (2) the ice is likely to be warmer, (3) the ice is heavily crevassed due to extending flow over a bedrock bump, and (4) the ablation rate and meltwater flux is higher. All four conditions imply that a traditional, ice-sheet marginal environment may be adequate for explaining previous observations of seasonal acceleration farther upstream, on the ice sheet flank.

March 6, 2007, 12 Noon

The Melting of Greenland
Bill Lipscomb, T-3, Climate, Ocean, and Sea Ice Modeling Group
TA-03, SM 200 (Advanced Computing Lab), CCS Conference Room, Room 116

The Greenland ice sheet appears to be losing mass, with outlet glaciers thinning and accelerating in response to recent warming. Models suggest that regional warming of a few degrees could initiate melting of the entire ice sheet, raising global sea level by 7 m over a number of centuries. As emphasized in the recent IPCC report, the rate of melting is extremely uncertain, because ice sheet models are crude and physical understanding is limited. I will summarize recent observations which suggest that the Greenland ice sheet could retreat significantly during the next several decades. I will then discuss observational and modeling challenges that must be overcome to make credible predictions of ice sheet melting and sea level rise, highlighting potential roles for LANL.