TL: GREENPEACE BRIEFING: THE THREAT OF SEA LEVEL RISE
SO: GREENPEACE INTERNATIONAL, (GP)
DT: JULY 1997

INTRODUCTION

According to the world's leading scientists, sea level rise is
"arguably one of the most important potential impacts of global
climate change." 1 Global average sea level has been rising over
the last 100 years, and global warming is expected to increase
the annual rate of sea level rise by two to five times. By the
year 2100, sea level is projected to be approximately 19 inches
higher than it is today. 2 An increase of this magnitude could
inundate coastal areas, erode beaches and exacerbate coastal
flooding. The costs associated with protecting shorelines in the
U.S. alone would be enormous.

Most of the increase in global sea level is expected to come
from thermal expansion of ocean water, followed by increased
melting of glaciers and ice caps. A major source of uncertainty,
however, concerns the polar ice sheets. Not only is there a lack
of understanding of their current mass balance, but there is
also considerable uncertainty regarding the ice sheets' possible
dynamic response to climate change. These uncertainties,
according to the United Nations' Intergovernmental Panel on
Climate Change (IPCC), make a very large difference in the
estimates of future sea level rise. 3

HUMAN INFLUENCE ON CLIMATE

Last year, the IPCC issued its landmark finding that human
activities have begun to significantly modify global climate.
The global average surface temperature has increased
approximately 1 degree F over the past century. IPCC predictions
indicate that the Earth will warm by an estimated 3.6 degrees F
by 2100. Even under the best-case scenarios, the rate of future
warming will probably be "greater than any seen in the past
10,000 years," according to the IPCC. 4

A variety of human activities -- notably, the burning of fossil
fuels -- produce greenhouse gases, like carbon dioxide (CO2),
nitrous oxide (N20), hydrofluorocarbons (CFCs, HCFCs, and HFCs),
methane (CH4), and sulfur hexafluoride (SF6). These emissions
trap the sun's heat and warm the planet, adding to the earth's
natural greenhouse effect. Carbon dioxide is by far the dominant
greenhouse gas produced through human activity: since
pre-industrial times, the concentration of atmospheric CO2 has
increased by 30 percent, from 280 parts per million to more than
360 parts per million. Measurements taken since 1959 show more
than a 12 percent increase in only 35 years. CO2 concentrations
will double by the end of the next century if emissions trends
continue unabated. 5

POLAR REGIONS' KEY ROLE IN GLOBAL CLIMATE

The polar regions' response to human-induced change is
critically important, since both regions play a key role in
global climate. Air, water and ice interactions in the Arctic
and Antarctica drive patterns of ocean circulation around the
globe and help regulate the energy balance of the global climate
system. The regions' snow and ice reflect heat and radiation
from the sun. Arctic permafrost stores one quarter of the
Earth's soil carbon. 6 Deep waters of the North Atlantic and the
circumpolar Southern Ocean remove carbon from the atmosphere,
storing it at great depths and influencing the level of CO2 in
the atmosphere.

POLAR REGIONS: VULNERABLE TO CLIMATE CHANGE

Scientists have long predicted that human-induced climate change
will have its first and most severe impacts in the polar
regions. The regions could warm between 1.5 to 4 times the
global average, a change which could have a significant effect
on ocean temperatures, water circulation, precipitation,
seasonal sea ice cover, and stability of ice sheets. 7 Changes
now occurring in these regions appear to be somewhat consistent
with these predictions. 

In the Arctic, large fluctuations in wildlife populations,
thinning sea ice over once-stable areas, rising lake
temperatures thawing permafrost and regional warming are a few
of the recent signs of change. Annual temperatures have
increased by about 4.5 degrees F in recent decades -- many times
the global rate -- over parts of Canada's western Arctic,
Alaska, and eastern Siberia. The most pronounced warming has
occurred during winter and spring, in areas such as Canada's
Mackenzie River Basin, the Bering Strait, and Lake Baikal in
Siberia. At the same time, paradoxically, temperatures are
currently cooling in the North Atlantic, a trend that is
consistent with climate change predictions. 8

Significant warming has occurred along the Antarctic peninsula
since the 1950s, and temperature measurements taken in the west
part of the continent show one of the greatest warming trends in
the southern hemisphere. 9 Other changes observed include
massive increases and decreases in wildlife populations,
thinning ice over some Antarctic lakes, and dramatic
disintegration and retreat of ice shelves. 10

While the exact causes are still unknown, these variations may
be an early signal of an early polar response to climate change.

POLAR CONTRIBUTIONS TO SEA LEVEL RISE

Just how much the polar regions will contribute to future sea
level rise is, as the IPCC indicates, a matter of great
uncertainty. Ocean levels have always fluctuated with changes in
global temperatures. During the ice ages, for example, when the
Earth was 9 degrees F colder than today, much of the ocean's
water was frozen in glaciers, and sea level was much lower than
its current level. During the last interglacial period (120,000
years ago) when the average temperature was 1.8 to 3.6 degrees
F warmer than today, sea level was significantly higher. 11

Over the past 100 years, the observed increase in global mean
sea level is an estimated 7 inches (within a range of 4 to 10
inches) according to the IPCC. The increase is largely
attributed to warmer global temperatures, which have expanded
ocean waters and melted glaciers, and ice caps. 12 The world's
areas of snow, ice and permafrost will continue to retreat; by
2100, between one-third and one-half of all mountain glaciers
could disappear. 13

There is one problem with predicting future retreat or melting
rate of the Greenland and Antarctic ice sheets: the ice sheets'
current mass balance largely remains a mystery. Scientists do
not yet understand how the ice sheets have contributed to
historical sea level, so it is difficult to predict a future
contribution with any certainty. Nevertheless, scientists do
know that relatively small changes in the ice sheets could have
a significant effect on sea level. 14 The Antarctic ice sheet is
particularly important, due to its sheer size -- 450 million
cubic miles.

GREENLAND 

Already, the margin of the Greenland ice sheet appears to have
retreated significantly over the past century, despite a
short-lived "thickening" of the ice during the 1970s and early
1980s. 15 Even under today's climate, in some places the ice
sheet is melting at a rate greater than the annual snowfall. 16 

Greenland's likely contribution to future sea level will depend
upon the amount of eventual warming in the region, and the
increases in precipitation and melting anticipated under higher
temperatures. The region may warm less than the global average,
or perhaps even cool, if the Gulf Stream weakens due to a "shut
down" in North Atlantic deep water formation. Nevertheless, most
experts expect Greenland temperatures to warm by more than the
global average. 17 

According to IPCC estimates, melting rates in Greenland should
add about 2.5 inches to global sea level by 2100. 18 Studies
show that sea level would rise 25 feet if the Greenland Ice
Sheet melted completely. 19 This scenario is highly unlikely,
but it illustrates the potential sea level impact caused by
changes in Greenland alone.

ANTARCTICA

Predictions about future Antarctic melting are much more
speculative. In Antarctica, air temperatures are expected to
warm by approximately 1.8-5.4 degrees F in the next century.
Warmer temperatures are not expected to cause significant
melting in the region, at least in the short-term. Instead,
warmer temperatures will bring increased precipitation and
snowfall, adding to the ice sheet mass and effectively slowing
sea level rise. 20 The IPCC's "best estimate" of projected
Antarctic ice sheet contribution to future sea level (by 2100)
thus remains slightly negative. 21 While short-term changes
cannot be ruled out, many experts believe that any Antarctic
melting, if it occurs, would take place over a substantially
longer time frame -- anywhere from 100 years to several
centuries -- lagging behind melting of glaciers and the
Greenland ice sheet. 22

 These long-term estimates notwithstanding, the Antarctic ice
sheet contains enough ice to raise global sea level over 180
feet, should it all melt. While it is unlikely that a major part
of the ice will disappear rapidly, shorter-term changes in ice
processes and dynamics induced by atmospheric warming could
still have world-wide effects on sea level. Warmer water
temperatures could have even further effects on the ice sheet.
Antarctica's contribution to sea level change over the next
century could vary from a slight decrease (-3.9 inches) to a
greater increase (+40 inches). 23

RECENT CHANGES ALONG THE ANTARCTIC PENINSULA

Since 1968, the rapid break-up of ice shelves along the
Antarctic peninsula has been considered as a sign that
"dangerous" warming has begun in Antarctica. 24 Capped in ice
and surrounded by floating ice shelves, the Antarctic peninsula
is more sensitive to climate change than the high, dry interior
Antarctic ice sheet. 25 Indeed, the Antarctica peninsula shows
a pattern of warming, with temperatures already increasing 4.5
degrees F since 1945. At the same time, five northerly shelves
have dramatically retreated as the region has warmed. 26
Glaciologists are not certain whether warming along the
peninsula is due to climate change or other factors. But given
the ice sheets' behaviour, some scientists believe that there
may
be an abrupt thermal limit on ice shelf viability, and that
regional atmospheric warming has moved this limit progressively
southward. 27 

In 1995, a prominent ice shelf on the peninsula, the North
Larsen ice shelf (Larsen-A), dramatically collapsed, casting
enormous icebergs into the Southern Ocean. The collapse followed
a period of steady ice shelf retreat, which coincided with a
regional atmospheric warming trend. Further south, the Larsen-B
shelf shows signs of imminent progressive retreat and other
dynamic changes. 28 The peninsula's Wordie ice shelf has
retreated so much in the past three decades that in 1989 all
that remained were two glacial remnants. 29 The Filchner and
Ross ice shelves have recently cast off huge icebergs. 30 

The reason for these changes is likely to be temperature
changes, but cannot be conclusively linked to global climate
change. Nevertheless, the Larsen collapse is at the very least
cause for concern. British Antarctic Survey scientists have
observed that "the temperature rise (on the Antarctic Peninsula)
is the fastest we have on record ... What we are seeing now are
changes only just working through to the glaciers and ice
sheets." 31

A POTENTIAL "STEPPED RESPONSE?" THE WEST ANTARCTIC ICE SHEET 

These recent events could indicate that there may be sensitive
thresholds which can lead to unstable ice sheet behaviour, to
sudden growth or collapse. Geologic and geomorphic studies of
ice sheets have long pointed to the importance of thresholds and
the way they lead to stepped growth and decay. Marine ice sheets
are particularly susceptible to sudden collapse, and some
scientists argue that there is a threshold which, if crossed,
might precipitate break-up of the Western Antarctic Ice Sheet.
Although the IPCC predicts a very low likelihood of collapse in
the next century, the consequences would be massive and
irreversible. 32

THE IMPACTS OF SEA LEVEL RISE

While much remains uncertain about Greenland and Antarctica,
future sea levels will rise as a result of global warming even
without any contribution from the world's great ice sheets.
Future changes in sea level will not occur uniformly around the
globe: locally and regionally, the rate, magnitude and direction
of sea level changes will vary substantially, due to different
patterns of ocean circulation, wind and pressure patterns, and
vertical movement of the land. 33

Current projections of sea level rise "should be of major
concern" for coastal zones and small islands, according to the
IPCC. Higher sea levels and warmer ocean temperatures are
expected to increase the chances of coastal flooding and storm
damage, erode shorelines and contaminate fresh water supplies.
Many of the world's beaches already suffer from erosion due to
sea level rise; future increases in sea level will erode shores
even further, affecting stable shorelines, as well. A rise in
sea level would also inundate coastal wetlands and coastal
barrier islands, and increase the salinity of estuaries. With
more than 70 percent of the world's population living on coastal
plains, the human and socioeconomic costs of rising seas could
be considerable. 34

In the U.S., a sea level rise consistent with IPCC's estimates
could drown up to 43 percent of coastal wetlands, erode beaches
100 to 200 feet, and inundate more than 5,000 square miles of
dry land -- an area the size of Connecticut -- by the year 2100.
The highest risk areas are those currently experiencing rapid
erosion rates and those at low elevation, particularly parts of
the Atlantic and Gulf coasts where sea level is already rising
by small amounts each year. By 2100, sea levels could rise 13
inches in Los Angeles, 20 inches in Miami Beach, 22 inches in
Boston, 38 inches in Galveston, and 55 inches in Grand Isle,
Louisiana. 35 Louisiana and Texas are already experiencing the
highest rates of relative sea level rise in the U.S. 36
Louisiana loses 25 square miles of wetlands per year, due to
subsidence. Sea level near Galveston is steadily increasing
Though the city was designed to withstand moderate sea level
rise, it could not withstand the levels predicted to result from
global warming. Along the Chesapeake Bay, where many beaches
have already been lost, the sea is rising more than an inch per
decade. 37 

Some parts of Florida's Everglades could disappear, as other
areas flood with salt water. Competition for diminishing
freshwater resources in southern Florida will surely result in
a "no-win situation" for the Everglades and the surrounding
human population, says the IPCC. 38  In California, rising sea
levels around San Francisco could further worsen salinity
problems in the San Joaquin Valley, the world's most productive
farming region. Groundwater pumping in the valley now exceeds
natural replenishment by more than a half trillion gallons a
year, forcing saltier water to seep into the delta from San
Francisco Bay. 39 

A significant and growing proportion of the U.S. population
lives within the coastal zone, with nearly half of all
construction between 1970 and 1989 occurring in coastal areas.
Protecting coastal property from the combined effects of erosion
and inundation could cost anywhere from $100 to $300 billion. 40

Impacts will be severe in other parts of the world, as well.
Many low-lying areas such as the Marshall Islands could be
completely inundated and made inhabitable. Seventeen percent of
Bangladesh could disappear with a three foot rise in sea level.
Up to 140 million people could be affected in China and
Bangladesh -- countries which regularly suffer heavy death tolls
from flooding. 41

Coral atolls and reef islands remain among the most sensitive
environments to long-term climate change and sea level rise,
according to the IPCC. 42 In the Pacific, there are growing
fears that rising seas could totally submerge whole island
nations such as Kiribati, the Marshall Islands, and Tuvalu,
whose land masses consists primarily of coral atolls. Other
island countries -- including Palau, Tonga, and the Federated
States of Micronesia -- could face severe freshwater shortages,
or lose much of their territory. Indeed, studies indicate that
islands in the South Pacific region will be "devastated" if
projected rises in sea level occur, their relatively small
economies effectively prohibiting the costs of adaptation. Faced
with the threat, over 35 island nations formed the Alliance of
Small Island States, which has argued for immediate reductions
in greenhouse gas emissions.

SEA LEVEL WILL CONTINUE TO RISE

Nearly all projections show that sea level will continue to rise
unabated beyond the year 2100 due to lags in climate response,
even if global greenhouse gas emissions are stabilized.
Estimates vary, but sea level could rise anywhere from 3 to 10
feet over the next few centuries. 43

CONCLUSION

The implications of warming on the Arctic and Antarctica are
complex and not yet fully understood. Yet they extend well
beyond these immediate areas, and may have dramatic global
repercussions, including dramatic increases in sea level. Local
warming may, in fact, accelerate global warming and its effects.
Potentially drastic changes in these regions serve as a wake-up
call to governments and individuals alike to take action now.
Greenpeace fully supports deep reductions in greenhouse gas
emissions, and a shift away from a fossil fuel-based economy to
one based on clean, renewable energy sources. These alternatives
have the potential to meet the world's energy needs, create
jobs, encourage world trade in clean technologies, and reduce
energy costs while protecting the planet. The barriers to these
solutions are not technical, but political. As nations seek ways
to cut greenhouse gases, Greenpeace calls on world leaders to
invest in, and implement, renewable energies and efficiency now,
for a sustainable planet tomorrow.

ENDNOTES

1 Intergovernmental Panel on Climate Change, Working Group I
Report, The Science of Climate Change, 1996, p. 364-365.

2 Ibid. The estimated range of sea level rise by 2100 is 5.1-37
inches, with a best estimate of 20 inches.

3 Ibid.

4 Ibid, p. 15.

5 Ibid, pp. 13-46.

6 Gunter Weller, Chapter on Arctic, in Encyclopedia of Earth
System Science, vol 1, Academic Press, Inc., San Diego, 1992.
See also W. Dwight Billings and Kim Moreau Peterson, Some
Possible Effects of Climate Warming on Arctic Tundra Ecosystems
of the Alaskan North Slope, in Robert L. Peters and Thomas E.
Lovejoy, Global Warming and Biological Diversity, Yale
University Press, New Haven, 1992, p. 236.

7 Colin Harris and Bennett Stonehouse, eds., Antarctica and
Global Climate Change, Belhaven Press, London (in association
with Scott Polar Research Institute, Cambridge), 1991, p. 90.

8 Arctic Research Consortium of the United States (ARCUS),
People and the Arctic: The Human Dimensions of the Arctic
System, Prospectus for Research, University of Alaska,
Fairbanks, 1997. See also Stewart J. Cohen, et. al., The
Mackenzie Basin Impact Study - Final Report, Environment Canada
and the University of British Columbia, Vancouver, BC, 1997; and
The Vulnerability and Role of the Arctic in Global Climate
Change, in Oil in Arctic Waters: The Untold Story of Offshore
Drilling in Alaska, publication of Greenpeace Alaska Field
Office, Anchorage, AK, 1996.

9 Olga Balashova and Bill Hare, Polar Meltdown: The Changing
Climate in Antarctica, a report prepared for Greenpeace
International, Stichting Greenpeace Council, Amsterdam,1997 p.
9.

10 Ibid, pp. 13-14. Ice "shelves" should not be confused with
ice "sheets." Ice shelves are masses of floating ice extending
into the ocean from glaciers or ice sheets. When they melt, they
do not directly contribute to sea level rise. Ice sheets are
grounded, and if they were to melt, they would increase sea
level. For example, when the great ice sheets of North America
and Eurasia melted at the end of the last ice age, sea levels
rose by about 300 feet.

11 James G. Titus and Vijay K. Narayanan, The Probability of Sea
Level Rise, U.S. Environmental Protection Agency, 1995, p. 138.

12 IPCC I 1996, op. cit., p. 363.

13 IPCC Working Group II Report, Impacts, Adaptations and
Mitigation of Climate Change: Scientific - Technical Analyses,
Climate Change Impacts on the Cryosphere (chapter 7), 1996. For
more information on glacial retreat, see also remarks of Ellen
Moseley-Thompson, Ohio State University/Byrd Polar Research
Center, in "Current Effects of Climate Change," An Ozone Action
Roundtable, Washington, D.C., June 24, 1996.

14 IPCC I 1996, op. cit., p. 374.

15 IPCC II 1996, op. cit., chapter 7.

16 Titus and Narayanan 1995, op. cit., p. 65.

17 Ibid, p. 124.

18 IPCC I 1996, op. cit., p. 381.

19 Titus and Narayanan 1995, op. cit., p. 65.

20 Ibid, p. 124-125.

21 IPCC I 1996, op. cit., p. 378.

22 Harris and Stonehouse 1991, op. cit., pp 17-18.

23 Ibid, p. 91.

24 Balashova and Hare 1997, op. cit., p. 15. For original
research see J.H. Mercer, Antarctic ice and Sangamon Sea level,
International Association of Scientific Hydrology, Snow and Ice
Commission, IAHS Publication no. 79:217-225 (1968).

25 Ellen Moseley-Thompson 1996, op. cit.

26 Balashova and Hare 1997 op. cit., p. 15. For original
research see D.G. Vaughan and C.S.M. Doake, Recent atmospheric
warming and retreat of ice shelves on the Antarctic Peninsula,
Nature, January 25, 1996, 379: 328-330. 

27 Ibid, p. 16.

28 Ibid.

29 Harris and Stonehouse 1991, op. cit., p. 61.

30 IPCC I 1996, op. cit., p. 374.

31 Jeremy Leggett, ed., Climate Change and the Financial Sector,
Gerling Akademie Verlag, Munich, 1996, p. 36.

32 Harris and Stonehouse 1991, op. cit., p. 16 and pp. 107-113.
See also Balashova and Hare 1997, op. cit., p. 21.

33 IPCC II 1996, op. cit., p. 297. See also Robert J. Nicholls
and Stephen P. Leatherman, Adapting to Sea-Level Rise: Relative
Sea-Level Trends to 2100 for the United States, Coastal
Management, 24:301-324, 1996.

34 IPCC II 1996, op. cit., Coastal Zones and Small Islands
(chapter 9).

35 Statement of David Gardiner, Assistant Administrator, Office
of Policy, Planning and Evaluation, U.S. Environmental
Protection Agency, before the U.S. House of Representatives
Science Committee/Energy and Environmental Subcommittee,
November 16, 1995

36 Nicholls and Leatherman 1996, op. cit., p. 309.

37 "Fragile Beaches Being Replaced by Armored Shore," Baltimore
Sun, May 25, 1997.

38 IPCC II 1996, op. cit.

39 Henry Vaux, Global Climate Change and California's Water
Resources, in Joseph B. Knox, ed., Global Climate Change and
California: Potential Impacts and Responses, University of
California Press, Berkeley, 1991.

40 Gardiner 1995, op. cit.

41 IPCC II 1996, op. cit., chapter 9.

42 Ibid.

43 IPCC I 1996, op. cit., p. 388; and Titus and Narayanan 1995,
op. cit.