Organization: National Aeronautics and Space Administration (NASA)

Research Title: Polar Programs

Funding Level (millions of dollars):

FY94	4.0
FY95	7.1
FY96	4.9

Committee on Environment and Natural Resources (CENR) Component:
(a) Subcommittee: Global Change Research Subcommittee (100%)
(b) Environmental Issue: Natural Variability and Long-Term Trends (90%) Compounding effects of environmental changes on natural hazards (10%)
(c) Research Activity: System Structure and Function: Observations (95%) Understanding (5%)

Organizational Component:
Science Division
Office of Mission to Planet Earth
NASA Headquarters
Washington, DC 20546

Point of Contact:
Robert H. Thomas
Phone: 202-358-1154
E-Mail: bthomas@hq.nasa.gov

Research Goals:
(a) To measure whether the major ice sheets (Antarctica, Greenland, and the Arctic ice caps) are growing larger or smaller. (b) To investigate the causes for observed changes.
(c) To estimate their current contribution to observed sea-level rise. (d) To develop models capable of providing reliable predictions of future ice-sheet response to prescribed changes in climate.

Program Interfaces:
The program has strong links with NASA's Crustal Dynamics & Physical Oceanography programs, with programs supported by other Agencies, particularly NSF, and with international primarily European programs. In addition, we enjoy excellent logistic support from the US Air National Guard and the Air Force. 1995: Survey of all major Canadian ice caps; established four Automatic Weather Stations on the Greenland ice sheet; airborne interferometric SAR measurements on the ice sheet; in situ measurements of ice velocity etc. along 1600 km transect of the ice sheet.

Program Milestones:
1991-1993: demonstration of a capability to measure ice-surface elevations over flight lines of up to 3000km; 1993/94, survey of the entire Greenland ice sheet at a flight-line separation of about 100km, and detection of short-term ice thickening over an active outlet glacier; 1993: demonstration of a capability for accurate aircraft measurement of ice thicknesses up to 3 km; 1994: 9-year time series showing a slight increase in melt extent over the Greenland ice sheet; Fall, 1994: international workshop to develop a long- term collaborative program of measurements to detect and interpret changes in the Greenland ice sheet.

Research Description:
This program three major components:

• Greenland ice-sheet surface topography surveys using precise airborne laser altimetry (45%). Repeat measurements after a 5-year interval will provide estimates of ice thickening/thinning rates. This work is done primarily by NASA/Wallops Flight Facility. A similar program in Antarctica is logistically unfeasible, and must await launch of a satellite laser altimeter, currently planned as part of EOS as the Geoscience Laser Altimeter System (GLAS) with a projected launch in 2002.

• Estimates of ice-sheet surface-elevation change from satellite radar altimetry (20%). Analysis of existing satellite data acquired since 1978 provides estimates of ice thickening/thinning over almost horizontal portions of the ice sheets; serious errors and ambiguities are introduced over sloping or undulating terrain. This work is done at Goddard Space Flight Center (GSFC) and at several universities.

• Mapping ice-sheet surface characteristics, such as melt zones and ice motion, and investigating associated processes (35%). Satellite data are used to map these zones, and surface measurements are made to develop sufficient understanding to model reliably the melt response to changing climate. This work is done at GSFC, Jet Propulsion Laboratory (JPL), and at universities. Within this program, we support a small modeling effort addressing overall ice-sheet response to climate. However, development of sophisticated models is premature until sufficient data have been acquired to support basic process studies and model validation.

Policy Payoffs:
Sea level is rising by about 2mm/yr, and we do not know why. Our uncertainty regarding ice-sheet mass balance is equivalent to a sea-level rise or fall of at least 2 mm/yr. Moreover, there are good reasons to suppose that parts of the big ice sheets are unstable, and could change rapidly regardless of climate change. Improved knowledge of present ice-sheet mass balance and an understanding of its causes will enable improvement both in predictive ice-sheet models and in initial conditions for model predictions, leading to more reliable estimates of future sea-level change. This has clear benefits for US coastal regions and for forewarning disasters abroad.