|
 Sea level rise has been one of the clearest signs of climate
change — water expands as it warms and parts of Greenland and
Antarctica are thawing, along with glaciers from the Himalayas to
the Alps.
But in a puzzle to climate scientists, the rate slowed to 2.4
millimeters (0.09 inch) a year from 2003 to 2011 from 3.4 mm from
1994-2002, heartening skeptics who doubt that deep cuts are needed
in mankind's rising greenhouse gas emissions.
Writing in the journal Nature Climate Change on Sunday, experts said
the rate from 2003-2011 would have been 3.3 mm a year when excluding
natural shifts led by an unusually high number of La Nina weather
events that cool the surface of the Pacific Ocean and cause more
rain over land.
"There is no slowing in the rate of sea level rise" after accounting
for the natural variations, lead author Anny Cazenave of the
Laboratory for Studies in Geophysics and Spatial Oceanography in
Toulouse, France, told Reuters.
In La Nina years, more rain fell away from oceans, including over
the Amazon, the Congo basin and Australia, she said. It is unclear
if climate change itself affects the frequency of La Ninas.
Rainfall over land only temporarily brakes sea level rise.
"Eventually water that falls as rain on land comes back into the
sea," said Anders Levermann, a professor at the Potsdam Institute
for Climate Impact Research, who was not involved in the study.
"Some of it goes into ground water but most of it will drain into
rivers, or evaporate."
HIATUS IN WARMING
The apparent slowing of sea level rise coincided with what the U.N.
panel of climate experts calls a hiatus in global warming at the
Earth's surface, when temperatures have risen less sharply despite
record emissions of greenhouse gases.
"The slowdown in sea level rise ... is due to natural variability in
the climate and is not indicative of a slowdown in the effects of
global warming," Nature Climate Change said.
[to top of second column] |
Many scientists suspect that the "missing heat" from a build-up
greenhouse gases in the atmosphere is going into the deep oceans as
part of natural variations in the climate.
But, because water expands as it warms, that theory had been hard to
reconcile with the apparent slowdown in sea level rise.
Sea levels have risen almost 20 cms since 1900. The U.N. panel of
climate experts expects an acceleration, with gains of between 26
and 82 cms over 100 years to the late 21st century.
Melting an ice cube with sides 7 kms (4.3 miles) long is roughly the
equivalent of adding a millimeter of water to the world's oceans.
Last year, another study said that unusually heavy downpours over
Australia in 2010 and 2011 had curbed sea level rise, before a
rebound reaching a rate of about 1 centimeter a year globally,
partly as water flowed back into the sea.
"It has tailed off in the past 12 months or so" to above 3 mm a
year, said John Fasullo of the U.S. National Center for Atmospheric
Research who was lead author of the Australia study.
For the Nature Climate Change study:
http://dx.doi.org/10.1038/nclimate2159
(Reporting by Alister Doyle; editing by Rosalind Russell)
[© 2014 Thomson Reuters. All rights
reserved.] Copyright 2014 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
 |
