OVER THE PAST TWO DECADES THE GREENLAND ICE SHEET HAS BEEN LOSING MASS AT AN INCREASING RATE AND IS TODAY CONTRIBUTING 2 MM/YR TO GLOBAL SEA-LEVEL RISE. HOW MUCH MASS THE GREENLAND ICE SHEET IS GOING TO LOSE OVER THE NEXT CENTURY AND BEYOND HAS BECOME ONE OF THE MOST URGENT QUESTIONS IN UNDERSTANDING THE CONSEQUENCES OF CLIMATE CHANGE. NUMERICAL MODELING IS OUR BEST TOOL TO ADDRESS THIS QUESTION. YET PREDICTING HOW FAST THE ICE SHEET IS MELTING HAS PROVEN TO BE INCREDIBLY CHALLENGING PRIMARILY BECAUSE IMPORTANT INPUT PARAMETERS AND PHYSICAL PROCESSES SUCH AS BASAL FRICTION OR CALVING DYNAMICS ARE POORLY KNOWN. WE PROPOSE HERE TO USE DATA ASSIMILATION BY COMBINING THE NASA-FUNDED ICE SHEET SYSTEM MODEL WITH AVAILABLE REMOTE SENSING DATA IN ORDER TO CAPTURE THE PAST AND PRESENT-DAY STATE OF ONE OF THE MOST RAPIDLY CHANGING SECTORS OF THE GREENLAND ICE SHEET: THE NORTHEAST ICE STREAM. THIS APPROACH WILL MAKE IT POSSIBLE TO BETTER UNDERSTAND THE PROCESSES DRIVING THE GLACIER RESPONSE TO CLIMATE CHANGE AND ULTIMATELY CONSIDERABLY REDUCING THE UNCERTAINTY IN FUTURE PROJECTIONS OF THE ICE SHEET CONTRIBUTION TO SEA LEVEL RISE.