Latest update on the world’s glaciers: Still shrinking
Last week provided a timely reminder that global temperatures – although important – are by no means the only sign of climate change. A preliminary report released by the World Glacier Monitoring Service shows a swathe of the planet’s glaciers are in retreat.
The new analysis, which provides the latest data for 2011, shows glaciers around the world are losing ice. But it also shows plenty of natural variation between different regions and from year to year.
This year’s report from the World Glacier Monitoring Service (WGMS) – just released – examined data from a selection of 108 glaciers including the Alps and the Andes, as well as others across North and South America, Europe and Asia.
As well as looking at year to year changes, the WGMS also monitors how glaciers are responding to rising global temperatures, which means looking at how glaciers change over successive decades.
Global decline
Let’s start by looking at what this year’s data show. Scientists at WGMS have been measuring 37 of the 108 glaciers continuously since about 1980. These ‘reference glaciers’ have the longest complete data record.
The scientists found that, on average, each reference glacier lost a volume of ice equivalent to one metre of thickness during 2011. This brings the total amount of ice lost up to more than 15 metres since 1980, with the rate of loss speeding up since about 2000.
The amount lost varied considerably between glaciers. According to the data, the Sarenne glacier in the French Alps lost the equivalent of four metres of thickness during 2011 – the biggest loss from a single glacier.
Glaciers lost ice across the rest of the world too, according to the data. Two of Greenland’s glaciers lost more than three metres between them. Twenty-three glaciers in Norway and Sweden lost about 28 metres in total. Another four glaciers in China, Japan, Russia and Spain also shrank during 2011.
In the southern hemisphere, eight glaciers across Argentina, Bolivia, Chile, Colombia, Kenya, New Zealand and Peru lost ice during 2011. One glacier in Bolivia called Chacaltaya vanished altogether.
Ups and downs
But looking at one year in isolation doesn’t tell us much about what’s happening to glaciers overall – a topic we’ve written more about this week in relation to global temperature. To find out what impact climate change is having on glaciers, scientists look at data over longer time periods.
For example, although nearly 80 per cent of glaciers monitored by WGMS lost ice during 2011, 25 glaciers across Canada, Iceland, the United States and Antarctica gained ice.
But WGMS data show that over a longer time period, glacier ice volume is decreasing overall in each of those countries. Here are the charts for Canada and six glaciers in the US showing culumative ice loss – you can see the others here.
Image - USA_glaciers (note)Image - Canada _glaciers (note)
Source: World Glacier Monitoring Service 2011 Bulletin
So why such variation? Glaciers react quickly to changes in atmospheric conditions, mainly temperatures, but also rainfall. This means the amount of ice that a glacier gains or loses can vary considerably from year to year and between different locations – depending on prevailing weather conditions.
Whenever a new scientific study finds that a glacier is growing, you can pretty much guarantee news stories questioning whether climate change is happening. But the new report shows why it’s important to look at more than one glacier for longer than a few years to avoid getting a misleading picture.
We’ve talked about this before when the media have jumped on a particular study without looking at whether or not it is representative of the longer term trend for that particular glacier and, more importantly, the global trend.
Long term decline
The graph below combines all the data collected since 1980 for the 108 WGMS glaciers in blue and the reference glaciers in red. Although there are wobbles reflecting the year to year fluctuations, both lines clearly show a decrease in glacier ice volume worldwide in the last three decades. The data also show that the rate of ice loss has accelerated since about 2000.
Image - Glaciers _decline (note)
Source: World Glacier Monitoring Service (WGMS)
In the same way as climate scientists analyse changes over short and long time scales – which is the difference between weather and climate – glaciologists are interested in looking at year to year fluctuations as well as the trend over several decades.
The WGMS is the most comprehensive ongoing study of glaciers worldwide. Next year will see a more detailed report from the body, which will discuss this year’s data further. But one thing that appears clear from the research is that on a global scale glaciers are shrinking, even with individual glaciers subject to year-to-year variation.