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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.

Andean _glaciers
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.

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