Glacier update: Andean glaciers melting faster due to climate change
- 22 Jan 2013, 15:00
- Roz Pidcock
A new study blames climate change for the retreat of glaciers in
the Andes. Glaciers in the region are losing ice faster than at any
time in the last 300 years. Some smaller glaciers are at risk of
disappearing altogether, the research concludes. So are glaciers
reaching a critical situation? We look at the new research in
context.
The Andes in South America are home to 99 per cent of the
world's tropical glaciers - those located high up in mountain
ranges around the equator. The new
study, published today in journal The Cryosphere, monitored
about half of all Andean glaciers across Colombia, Bolivia, Peru
and Ecuador to see how the volume of ice they contain has changed
since the 1970s.
The scientists used field measurments and satellite data to
survey an area of almost a thousand square kilometres, making the
new study the most comprehensive review of Andean glaciers so
far.
Andean meltdown
The research showed although there have been some "sporadic
gains" in ice mass for several glaciers in the survey region,
overall they are in decline. On average, the glaciers lost about 30
to 50 per cent of their mass since the 1970s, and the rate they are
shrinking is accelerating. According to the study, the rate of
melting is now unprecedented in the last 300 years.
The black line in the plot below shows the average percentage of
ice lost each year for all the Andean glaciers studied. The
different colours refer to the rate of ice loss for Bolivia,
Peru, Colombia, Venezuela and Ecuador.
Source: Rabatel et al., (2012)
Small glaciers at low altitudes are the most vulnerable to
melting, according to the study. Glaciers less than 5,400 metres
above sea level have lost about 1.35 meters in ice thickness every
year since the late 1970s - around twice the melt rate of those
higher up.
As Antoine Rabatel, researcher at the Laboratory for Glaciology
at the University of Grenoble and lead author of the study
explains, this rate of ice melt means smaller glaciers might not be
around for much longer:
"Because the maximum thickness of these
small, low-altitude glaciers rarely exceeds 40 metres, with such an
annual loss they will probably completely disappear within the
coming decades."
Temperature rise is to blame
Glaciers react quickly to changes in atmospheric conditions,
which means the amount of ice can be affected by either changes in
temperature or rainfall. It's this sensitivity that makes
glaciers good visible indicators of climate change, a point made in
the IPCC's
4th Assessment Report.
But as Rabatel explains in the paper, rainfall patterns are
unlikely to have caused the observed changes in the Andean
glaciers:
"Precipitation did not display a
significant trend in the tropical Andes in the 20th century, and
consequently cannot explain the glacier recession."
The researchers put the blame for the rapidly retreating
glaciers squarely on
rising global temperature, coming to the conclusion in the
paper that "atmospheric warming is the main factor explaining the
current glacier recession". Temperatures in the region rose by 0.15
degrees Celsius per decade between 1950 to 1994, equivalent to 0.7
degrees overall.
Global decline
As we said in a blog post
earlier this week, it's not enough to look at just one region
to find out what's going on globally. To get a more global picture,
scientists study glaciers in lots of different locations for a
number of decades.
But while scientists tend to be cautious about using data from a
single region to make general statements about the impact of
climate change on glaciers, it does seem that the situation in the
Andes reflects the declining global trend.
Last week, the World Glacier Monitoring Service (WGMS) released its
latest analysis of
108 glaciers across the globe. It found glaciers retreating
worldwide, losing a total of more than 15 metres of ice thickness
equivalent since 1980.
This news supports the IPCC's conclusion from its 2007
Fourth Assessment Report, which said:
"During the 20th century, glaciers and
ice caps have experienced widespread mass losses and have
contributed to sea level rise ... This is expected to continue
during the next 100 years."
The new Andean study also found that the rate of ice loss varied
a lot from year to year, depending on prevailing weather and ocean
circulation conditions. Some glaciers temporarily gained ice for
one or two years.
This is why its important to look at changes over successive
decades rather than just a few years to avoid getting a misleading
picture. You can read more
here.
Water shortages
Retreating glaciers aren't just a visible indication of climate
change - there are practical consequences, too. Another author of
the new study, Alvaro Soruco, says the Andean glaciers are an
important source of fresh water for nearby populations:
"Glaciers provide about 15 per cent of
the La Paz water supply throughout the year, increasing to about 27
per cent during the dry season."
Rabatel explained to Carbon Brief today that as well as
domestic consumption, the supply of water from mountain glaciers is
important for agriculture and hydropower. So water
shortages could become more problematic for local communities if
the ice melt doesn't stop soon.
Successive studies show that glaciers are melting in response to
climate change. But there are still relatively few studies like
this one, with data spanning several decades. Such research is
invaluable to climate scientists looking to get an idea of the full
impact of rising temperatures are having on the world's glaciers -
and what to expect in the future.