1. Sea Level Rise The Coast to Come

2. What We Know  Only a few centimeters of sea level rise can produce major changes for coasts.  In low-lying areas, a half a meter vertically can translate to inundation far from the present shoreline.  On the scale of centuries, a few degrees of global warming could generate 10s of centimeters of global sea level rise.

3. What We Know (cont’d)  The oceans' influx of water is caused by thermal expansion of warmer water, and terrestrial meltwater.  Scientists understand thermal expansion and glacial and small ice cap melting fairly well.  These sources of meltwater were responsible for the majority of 20th century sea level rise, and they will continue to be critically important.

4. The Unknowns  Scientists face more of a challenge to understand the ice sheets on Antarctica and Greenland and all of the factors affecting how, where, and how much the ice sheets will melt and how much of that will reach the ocean.

5. The Unknowns  That isn't the only difficulty. As the weight of ice is lifted off land, the land tends to rise, counteracting the effect of melting in the vicinity of the sheet.  There also seems to be an uncorking effect that comes when ice shelves - the rafts of floating sea ice that formerly blocked up coastal glacier outlets - disappear.  Once these protective dams collapse or melt, rivers of glacial ice seem to accelerate toward the sea, though scientists do not yet fully understand these dynamics.

6. The Unknowns (cont’d)  Some recent data suggest sea levels may be trending toward the higher end of IPCC estimates (or even beyond), because meltwater contributions from Greenland and Antarctica have increased in recent years.  Some models that have incorporated these new data project that sea level could rise by 3 to 4 ft. (0.9 to 1.2 m.) by 2100.

7. The Unknowns (cont’d)  However, scientists do not yet agree on which models will be the most accurate on this point, as research on ice sheet behavior is still in its early stages.  As a result, most guidance calls for planners and policy makers to plan for a range of possibilities, noting that the risk of global mean sea level rising by more than 1 m by 2100 cannot be excluded.

8. Rates of Rise  Sea level rise will not rise at the same pace everywhere.  Depending on local conditions, sea level rise could be much less than a meter, or much more.

9.  Sea levels rose unevenly along the coasts of the United States between 1958 and 2008.  On the Mid-Atlantic coast and parts of the Gulf coast, sea levels rose noticeably, by as much as 8 inches.  In Alaska and the Pacific Northwest, on the other hand, sea levels fell in many places, because the land is rising faster than the sea in this region. Rates of Rise

10. Cost of Rising Seas  The consequences of sea-level rise may be expensive.  In 1991, the Federal Emergency Management Agency calculated that a one-foot sea level rise by 2100 would increase annual flood damage to insured property by 36- 58%.

11.  A separate study more recently calculated that a rise of almost 20 in. (0.5 m) by 2100 would cause $23- 170 billion in damage.  It is also worth remembering that sea level rise will not stop in 2100. Without significant deviation from our present course of greenhouse gas emissions, sea level rise will continue for several thousand years. Cost of Rising Seas