Sea level may rise more than 1m by 2100
Julio Godoy | Berlin, Germany
31 December 2006 06:00
Ocean levels will rise faster than expected if greenhouse-gas
emissions continue to rise, a leading German researcher warns.
Using Nasa data, Stefan Rahmstorf, professor of physics of the oceans
at the University of Potsdam near Berlin, estimates that the sea
level could rise by 140cm by 2100.
Rahmstorf, a member of the German Advisory Council on Global Change,
is considered a leading European researcher on global warming and its
effect on oceans.
"The semi-empirical model we used to process Nasa data showed a
proportional constant sea level rise of 3,4mm per year per degree
Celsius," Rahmstorf said. "Then we applied this constant
proportionality to future earth-surface warming scenarios of the
Intergovernmental Panel on Climate Change [IPPC], and came to
estimate that by the year 2100, sea level could rise between 50cm and
140cm above the level measured in 1990."
Through the 20th century, global warming led to an average 20cm rise
in sea level. But most computer models of climate change used at
present significantly underestimate sea-level rise, Rahmstorf
said. "Future projections of sea level based on these climate models
are therefore unreliable."
Currently, sea level is rising at 3cm per decade, faster than
projected in the scenarios of the IPCC third assessment report,
The IPCC, an intergovernmental team of scientists carrying out a wide
range of research related to climate change, was established in 1988
by the World Meteorological Organisation and the United Nations
Environmental Programme. It aims to assess scientific, technical and
socio-economic information relevant for understanding of climate
change, its potential impact and options for adaptation and
Scientific research has found that industrial activities have
produced greenhouse-gas emissions considerably higher than levels
observed before the industrial revolution.
Concentration of carbon dioxide, the most potent of greenhouse gases,
has risen from about 280 parts per million (ppm) in the atmosphere in
the year 1750 to about 380 ppm today.
This rise is primarily due to the burning of fossil fuels and, to a
lesser extent, deforestation. Scientists estimate that if the present
emissions trend continues, the atmosphere could heat up by about five
degrees Celsius by 2100.
Studies by the Potsdam Institute for Climate Impact Research suggest
that this would roughly be the temperature difference between an ice
age and a warm stage. But while the rise of average temperatures by
about five degrees between the last great ice age and today took 5
000 years, the new global warming would need only 100 years.
Rahmstorf acknowledged that forecasts of global warming and its
effects on sea levels continue to be marked by uncertainty. "The fact
that we get such different estimates using different methods shows
how uncertain our sea level forecasts still are," Rahmstorf said.
A major reason for the uncertainty is the behaviour of the large ice
sheets in Greenland and Antarctica.
A likely consequence of a massive melting of the ice masses on the
North Pole could be the breakdown of the North Atlantic Current. The
current is the northern extension of the Gulf Stream, and constitutes
a warm-water current flowing between Britain and Iceland. This has
considerable effect in moderating the north European and Scandinavian
"One critical factor for the continuation of this current is the
amount of fresh water that enters the northern Atlantic region in the
future," Rahmstorf said. "This will depend in large part on the speed
at which Greenland's ice sheet melts."
Rahmstorf, who earlier this year co-authored a research paper titled
The Future Oceans: Warming Up, Rising High, Turning Sour, said
reliable prediction on the risk of a total stoppage of deepwater
formation in the northern Atlantic is not possible given present
But he pointed out that experts have evaluated that risk at more than
50% if global warming is between three and five degrees Celsius.
Rahmstorf said greenhouse-gases emissions are also increasing the
acidity of oceans. "In the atmosphere, carbon dioxide does not react
with other gases, but in the ocean it dissolves, contributing to the
acidification of seawater," he said. This acidity is a serious threat
to marine biodiversity.
"There is a good chance to avoid such dangerous climate change if
global warming caused by human activities is limited to two degrees
in the coming decades," Rahmstorf said. -- IPS