The little
white shack at the water’s edge in Lower Manhattan is unobtrusive —
so much so that the tourists strolling the promenade at Battery
Park the other day did not give it a second
glance.
Up close, though, the roof of the shed
behind a Coast Guard building bristled with antennas and other
gear. Though not much bigger than a closet, this facility is
helping scientists confront one of the great environmental
mysteries of the age.
The equipment
inside is linked to probes in the water that keep track of the ebb
and flow of the tides in New York Harbor, its readings
beamed up to a satellite every six
minutes.
While the gear today is of the latest
type, some kind of tide gauge has been operating at the Battery
since the 1850s, by a government office originally founded
by Thomas Jefferson. That long data record has become invaluable to
scientists grappling with this question: How much has the ocean
already risen, and how much more will it go
up?
Scientists have spent decades examining
all the factors that can influence the rise of the seas, and their
research is finally leading to answers. And the more the scientists
learn, the more they perceive an enormous risk for the United
States.
Much of the population and economy of
the country is concentrated on the East Coast, which the
accumulating scientific evidence
suggests will be a global hot spot for a rising sea level over the
coming century.
The detective
work has required scientists to grapple with the influence of
ancient ice sheets, the meaning of islands that are sinking in the
Chesapeake Bay, and even the effect of a giant meteor that slammed
into the earth.
The work starts
with the tides. Because of their importance to navigation, they
have been measured for the better part of two centuries. While the
record is not perfect, scientists say it leaves no doubt that the
world’s oceans are rising. The best calculation
suggests that from 1880 to 2009, the global average sea level rose
a little over eight inches.
That may not
sound like much, but scientists say even the smallest increase
causes the seawater to eat away more aggressively at the shoreline
in calm weather, and leads to higher tidal surges during storms.
The sea-level rise of decades past thus explains why coastal towns
nearly everywhere are having to spend billions of dollars fighting
erosion.
The evidence suggests that the
sea-level rise has probably accelerated, to about a foot a century,
and scientists think it will accelerate still more with the
continued emission of large amounts of greenhouse
gases into the air. The gases heat the planet and cause
land ice to melt
into the sea.
The official
stance of the world’s climate scientists is that the
global sea level could rise as much as three feet by the end of
this century, if emissions continue at a rapid pace. But some
scientific evidence supports
even higher numbers, five feet and beyond in the worst
case.
Scientists say the East Coast will be
hit harder for many reasons, but among the most important is that
even as the seawater rises, the land in this part of the world is
sinking. And that goes back to the last ice age, which peaked some
20,000 years ago.
As a massive
ice sheet, more than a mile thick, grew over what are now Canada
and the northern reaches of the United States, the weight of it
depressed the crust of the earth. Areas away from the ice sheet
bulged upward in response, as though somebody had stepped on one
edge of a balloon, causing the other side to pop up. Now that the
ice sheet has melted, the ground that was directly beneath it is
rising, and the peripheral bulge is
falling.
Some degree of sinking is going on all
the way from southern Maine to northern Florida, and it manifests
itself as an apparent rising of the
sea.
The sinking is fastest in the
Chesapeake Bay region. Whole island communities that contained
hundreds of residents in the 19th century have already disappeared.
Holland Island, where the population peaked at nearly 400 people
around 1910, had stores, a school, a baseball team and scores of
homes. But as the water rose and the island eroded, the community
had to be abandoned.
Eventually just
a single, sturdy Victorian house, built in 1888, stood on a
remaining spit of land, seeming at high tide to rise from the
waters of the bay itself. A few years ago, a Washington Post
reporter, David A. Fahrenthold, chronicled
its collapse.
Aside from this general sinking of land
up and down the East Coast, some places sit on soft sediments that
tend to compress over time, so the localized land subsidence can be
even worse than the regional trend. Much of the New Jersey coast is
like that. The sea-level record from the Battery has been
particularly valuable in sorting out this factor, because the tide
gauge there is attached to bedrock and the record is thus immune to
sediment compression.
Perhaps the
weirdest factor of all pertains to Norfolk, Va., and points nearby.
What is now the Tidewater region of Virginia was slammed
by a meteor about 35 million years ago — a collision so
violent it may have killed nearly everything on the East Coast and
sent tsunami waves crashing against the Blue Ridge Mountains. The
meteor impact disturbed and weakened the sediments across a 50-mile
zone. Norfolk is at the edge of that zone, and some scientists
think the ancient cataclysm may be one reason it is sinking
especially fast, though others doubt it is much of a
factor.
Coastal flooding has already become
such a severe problem that Norfolk is spending millions to raise
streets and improve drainage. Truly protecting the city could cost
as much as $1 billion, money that Norfolk officials say they do not
have. Norfolk’s mayor, Paul Fraim, made headlines a couple of years
ago by acknowledging
that some areas might eventually have to be
abandoned.
Up and down the Eastern Seaboard,
municipal planners want to know: How bad are things going to get,
and how fast?
One of the most ambitious attempts to
take account of all known factors came just a few weeks ago from
Kenneth
G. Miller and Robert
E. Kopp of Rutgers University, and a handful of their
colleagues. Their calculations,
centered on New Jersey, suggest this is not just some problem of
the distant future.
People
considering whether to buy or rebuild at the storm-damaged Jersey
Shore, for instance, could be looking at nearly a foot of sea-level
rise by the time they would pay off a 30-year mortgage, according
to the Rutgers projections. That would make coastal flooding and
further property damage considerably more likely than in the
past.
Even if the global sea level rises only
eight more inches by 2050, a moderate forecast, the Rutgers group
foresees relative increases of 14 inches at bedrock locations like
the Battery, and 15 inches along the New Jersey coastal plain,
where the sediments are compressing. By 2100, they calculate, a
global ocean rise of 28 inches would produce increases of 36 inches
at the Battery and 39 inches on the coastal
plain.
These numbers are profoundly
threatening, and among the American public, the impulse toward
denial is still strong. But in towns like Norfolk — where
neighborhoods are already flooding
repeatedly even in the absence of storms, and where some
homes have become unsaleable — people are starting to pay
attention.
“In the last couple or three years,
there’s really been a change,” said William A. Stiles Jr., head of
Wetlands
Watch, a Norfolk environmental group. “What you get now
is people saying, ‘I’m tired of driving through salt water on my
way to work, and I need some solutions.’
”