The Ice Age postponed? Impacts of melting ice in a warming world
How is climate change affecting the world’s glaciers?
What changes have occurred so far?
Why do melting glaciers matter for people?
Compared with other types of environments, glacial environments are ‘the canary in the coalmine’ for detecting global warming. In other words, these environments are particularly sensitive to the recent phase of atmospheric warming that is being caused by rising levels of greenhouse gases in the atmosphere due to fossil fuel burning and the clearing of forests (mainly tropical deforestation).
Since the industrial revolution in the 18th century, the concentration of carbon dioxide in the atmosphere (an important greenhouse gas) has risen significantly above the level it would be naturally. It now stands at over 400 parts per million (ppm) in the atmosphere. Evidence from ice cores (see Lesson four) tells us that the normal level for CO2 in the atmosphere during ‘interglacial’ times (such as the Holocene in which we now live) is 270 to 290 ppm, and that at no time over the last 800,000 (the time covered by ice cores) has the CO2 level been as high as it is now. (CO2 is thought to be at its highest level for three to five million years.)
As CO2 and other greenhouse gases have increased and the Earth’s average surface air temperature has risen, the rate of ‘ablation’ (see Lesson two) for most glaciers has increased. In many glacial environments this has resulted in a ‘negative mass balance’ causing glaciers to shrink (leading to ‘deglaciation’ of glacial areas).
With this change, we can expect various impacts: sea level will continue to rise; some areas will lose a steady water supply as glaciers disappear, rock falls, floods, and avalanches will become more frequent in mountain regions, and economic activities will be affected.
Glaciers are sensitive to climatic changes because their sizes are controlled by the balance between ‘accumulation’ and ‘ablation’; and in turn, these processes are closely linked with snowfall and air temperature. For a refresher on this idea, see the interactive diagram in Lesson two that allows you to adjust these factors to see how a glacier responds.
Because of this, glaciers across the world are being studied and measured to help us understand how the climate is changing. Other parts of the ‘cryosphere’ (Lesson one) are also sensitive to climate change: for instance, the area of sea ice in polar seas and the area of permafrost on land are also declining.
In general, high-latitude and polar regions are experiencing more rapid warming than other parts of the world, and one of the reasons for this is the loss of ice. There is a ‘feedback’ at work: snow and ice makes a reflective surface that bounces much sunlight back to space. However, as warming melts ice and as ocean and land surfaces are exposed, reflection is reduced. More of the Sun’s energy is absorbed by the surface, causing further warming.
Download and look through the Cryosphere changes PowerPoint slides. Once you have done so, discuss the following questions in your class.
What changes have been happening to the cryosphere over recent decades?
How does the trend in global average air temperature compare with the trend in Arctic sea ice?
What is happening to most of the world’s glaciers? Comment on any exceptions, and can you think of reasons for the exceptions?
For those of us who live far from glaciers, the changes affecting them may seem a remote and minor problem with little relevance for our own lives. However, this is a misconception: shrinking glaciers will have affects far beyond the glacial environments where they are located, and there are important ways in which this will matter for us and our descendants.
Go to the BBC website and click on the ‘shrinking glaciers’ video clip.
Why is the Greenland ice sheet likely to continue melting?
How are most glaciers likely to change in years ahead?
These changes are affecting, and will continue to affect, people in many different ways. At the global scale, anyone living along the coast near sea level will be affected because melting glaciers contribute to sea level rise. While much of recent sea level rise has been due to the sea expanding as it warms, the contribution from melting glaciers is also important and set to increase.
Sea level rise is a slow process (about three mm per year at present) but one that could gradually have major impacts on many coastal cities. Already we are beginning to see how, with higher sea levels, storm-related coastal flooding is becoming more hazardous. On the 29th of October, 2012, Hurricane Sandy caused a sea surge to flood much of New York City, and the economic damage to the USA caused by this storm was second only to Hurricane Katrina in 2005.
Over the winter storms of 2013/2014 in England, the Thames Barrier had to be closed over 40 times to protect London from flooding due to a combination of heavy rains and high tides – when being designed in the 1970s, the barrier was only expected to be used two or three times a year!
The future for sea level rise depends mainly on what happens to the Antarctic and Greenland ice sheets, as together they account for the vast majority of the world’s glacier ice. Both the West Antarctic and Greenland ice sheets are losing mass, and the concern is that their retreat will become irreversible: even if the world could stop emitting greenhouse gases tomorrow, inertia from the sea level rise and warming already under way could make the shrinking of these ice sheets unstoppable for hundreds of years into the future.
Although uncertain, sea level could rise by a half metre to as much as a metre or so by AD 2100, with continued rise over many centuries to come. The survival of some low lying, island nations (such as the Maldives) is at stake, and huge sums of money will need to be spent to protect coastal cities around the world. Go to Discovering Antarctica website to learn more about parts of the world that are vulnerable to sea level rise.
If the Greenland ice sheet disappeared completely, a process that would take thousands of years, another seven metres would be added to sea level. Go to this website where you can visualise the changes to world coastlines caused by different amounts of sea level rise. Try ‘+60m’ to see what coastlines would be like if the Antarctic ice sheet didn’t exist.
Aside from global impacts, there are also regional and local impacts of melting ice. About a billion people around the world rely on water from mountain glaciers for home use and irrigating farmland. A good example is the city of Lima in Peru. This city of about eight million people is located in a hyper arid desert and is reliant on meltwater that flows down from the Quelccaya ice cap in the high Andes. Worryingly, this ice cap has shrunk by about 30% in the last 30 years. Glacial areas are the source of many major rivers of the world, and summer melt from mountain glaciers helps to sustain river flow during dry seasons.
Another impact of the shrinking of mountain glaciers is an increase in flash flooding and hazards of ‘mass movement’ (such as rock falls and landslides). Rapid flood events (called ‘glacial outburst floods’) can occur when glacial meltwater trapped behind a natural dam builds up and reaches a critical volume, causing the water to burst through the barrier and flood the valleys below. Thawing ground loosens rocks on mountain slopes, causing them to fail more easily.
At a more local level, shrinking glaciers can also mean shrinking revenue at places (such as in the Alps) where there is a tourist industry based around glaciers and winter sports.
Download the Human impacts task to review and learn more about the problems related to shrinking glaciers.
Not only is deglaciation a form of evidence of climate change, we have also seen how this process of glacier shrinking and retreat leads to a range of different types of impacts on people.
To finish this lesson, read these sources about wrapping glaciers and consider the following questions in class discussion:
Go to BBC News website
Go to Phys.org website
Go to Guardian website
Why are some glaciers being wrapped up in the summer?
What are the arguments for and against taking this approach towards preserving glaciers?
How far do you think deglaciation is a process that people can control as opposed to something people will have to adapt to?
||This resource has been developed as part of the Rediscovering London's Geography project, funded by the GLA through the London Schools Excellence Fund. It seeks to improve the quality of teaching and learning of geography in London’s schools, in addition to encouraging more pupils to study geography