Melting glaciers: unexpected boost to rising oceans
- Melting glaciers: unexpected boost to rising oceans
By Peter N. Spotts
Staff writer of The Christian Science Monitor
Few effects from global warming raise more red flags than rising sea
levels. The topic has led to a growing pile of conflicting research
trying to answer the questions: How fast, and why?
Now, a pair of US scientists conclude that the oceans rose at a
global average rate of 1.5 to 2 millimeters a year (6 to 8 inches a
century), confirming a hotly debated, decade-old estimate. But their
work also points to the key driver of this change: water from melting
glaciers and not, as some have argued, a natural swelling of the
oceans caused by higher temperatures.
Pinpointing glacial melt as the leading source of the oceans' rise is
a new finding that contradicts several past studies.
The work "is a major contribution, and will go a long way toward
explaining some of the current enigmas in our understanding of the
earth's system," says Mark Meier, a glacier expert at the University
of Colorado at Boulder.
"This was a surprise to us," says Laury Miller, an oceanographer with
the National Oceanic and Atmospheric Administration's Laboratory for
Satellite Altimetry in Silver Spring, Md. "But it just popped out of
the data." And, he notes, it dovetails with studies that show oceans
now contain more fresh water than 40 years ago.
The difference between these findings and the findings of other
scientists who argue for a slower, 4-inch-per-century rise in sea
level may seem small, Dr. Miller notes, but it's significant. More
than 100 million people worldwide live within a mile of a coastline
and would be first affected by any rise.
"The estimate for the past 100 years forms the basis for future
predictions" of the impact of changing climate on the world's oceans,
he says. Miller and Bruce Douglas of Florida International University
conducted the study, which appears in Thursday's edition of Nature.
The debate over the rate of the oceans' rise emerged in the mid- to
late 1990s, researchers say. The Intergovernmental Panel on Climate
Change (IPCC), which distills the latest research and lays out
related policy issues for government leaders, noted in 1995 that the
best evidence argued for an increase of 6 to 8 inches a century. The
gains were measured at tide gauges worldwide.
Improved measurements of global ocean heat, however, indicated that
the ocean had not warmed nearly enough to rise at the rate the tide
gauges indicated. And glacial runoff was still thought to be a tiny
contributor to ocean mass.
The situation grew muddier with a study published in 2002 by French
researchers who compared satellite data with a new catalog of ocean
temperature and salinity estimates and concluded that tide gauges
overestimate the rate of sea-level rise.
Miller and Douglas, by contrast, used the tide gauges and raw
oceanographic measurements of temperature, salinity, and density to
reach their conclusions.
The tide gauges do not appear to be unduly influenced by local
conditions, and the combined sources of direct data argue for the
higher rate of increase, they say, and glacial melt as the leading
FRESHWATER SOURCE: New evidence shows oceans are rising 6 to 8 inches
per century, mainly because of melting glaciers, such as this one in