Global Sea Level Rise Sandra Ashhab & Ram Fishman December 5th 2006

Why is GSL rising ? Volume increase – Warmer water expands in volume in proportion to its initial volume and the temperature change.

2. Mass increase- Precipitation continually transports water mass from the oceans and land locks them in continental glaciers and ice sheets over Greenland and Antarctica (8mm a year) Melting (glaciers) and Iceberg discharge returns water to the oceans. Global warming affects temperature and precipitation patterns and can change this mass balance. Melting sea ice does not raise sea level (Archimedes’ principle) Both mass increases and volume increases are due to increasing temperatures.

20th century GSLR - Measurements Tide Gauges Average rate of 1.5-2 mm/yr over 20th century Satellite altimeters ~2.5 mm/yr since 1992 ref: IPCC & Miller et al 2004

20th century GSLR - Estimates Volume- 0.5 (0.3 -0.7) mm/yr (Based on T-S measurements). Mass- 0.2-0.4 mm/yr from glaciers and ice caps - 0.1-0.5 from Greenland and Antarctica Other evidence suggests 1.4 mm/year freshening ref: IPCC

21st century GSLR Projection – Volume increase IPCC: 0.11-0.43 meters Depending on the Emission scenarios and the model. Example: Scenario – corresponding 21st C. GSLR B1- 13-18 cm A1B- 18-25 cm A2 – 19-30 cm Meehl et al 2005

21st century GSLR Projection – Mass Increase IPCC: Glaciers: 1 to 23 cm Greenland: -2 to 9 cm Antarctica: -17 to 2 cm Glaciers melting sensitive to temperature Antarctica – sensitive to increased precipitation

Take-home points Accelerating rates of GSLR (from both mass and volume increase) are related to anthropogenic factors i.e. GHG emissions and global warming Conventional projections of GSLR during the 21st century are in the order of 50 cm due to mass and volume increase together. Future estimates are subject to uncertainty because they depend on different temperature projection which depend in the first place on different GHG emission scenarios. Other factors can cause uncertainty such as glaciers sliding to the ocean that contribute to glacier mass loss but not necessarily contribute to SLR The Greenland and Antarctic ice sheets together have the potential to raise sea level by as much as 70 m, so that only a small fractional change in their volume would have a significant effect on the GSL. GSL will continue to rise for centuries even after GHG concentrations stabilize, so that its eventual effect can be significantly larger than might seem during this century.