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Observations
Temperature increases are not the only effects of climate change that are currently being observed. With the help of instrumentally recorded data, satellites and a range of other observational tools, we are able to monitor and identify many other changes occurring around the planet. Examples of these effects range from sea level rise, to melting sea ice and glaciers, to thawing permafrost. The effects of climate change are not limited to these examples alone, but we will limit our discussion here to these widely observed and discussed effects.
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Sea level
The global average sea level rise over the course of the twentieth century has been approximately 0.17 meters (1). The global sea level rose approximately 1.8 mm per year between 1961 and 2003 and rose about 3.1 mm per year between 1993 and 2003. As with the global average temperature trends, the global average sea level is rising at an accelerated rate in recent years.
Figure 2: Global average sea level change in mm relative to 1961-1990 levels. Sea level change obtained from tide gauge data (blue) and satellite data (red). (after IPCC3)
There are various factors responsible for contributing to sea level rise, such as thermal expansion, glacier melt contribution, and the Greenland and Antarctic ice sheet melt contribution.
Thermal expansion
When heated, water expands. As the Earth’s atmosphere warms, so do the oceans. Simply put: the atmosphere is warming, causing the oceans to warm. Because the oceans are warming, they are expanding, which causes the sea levels to rise.
The fact that sea levels rise in response to ocean warming is not good news, considering that global average temperatures are expected to continue to rise in the future. Another problem is that the oceans experience a lag in warming, due to their strong thermal inertia. This means that even if temperatures were to stop rising and stabilize, sea levels will continue to rise for some time into the future.
Glacier and ice sheet melt
Melt water from the Greenland ice sheet, the Antarctic ice sheet and from glaciers are all contributing factors to rising sea levels. As temperatures warm, ice sheet and glacier melt increases. The world’s ice sheets and glaciers hold an enormous amount of water, and thus have the potential to contribute significantly to future sea level rise.
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Arctic sea ice
Sea ice is an important part of the Arctic landscape. It provides habitat space for many species of birds and animals, as well as important hunting and breeding space. Sea ice also plays an important role in the climate, due to its highly reflective properties (albedo). As sea ice diminishes in extent, so does its ability to reflect radiation back from the surface. This speeds the warming experienced in the area, as more solar radiation is absorbed by lower albedo surfaces (such as open water).
Sea ice extent in the Arctic is measured by satellite. Since 1979, it has been observed that Arctic sea ice that survives through the summer has decreased by approximately 7.4% per decade (2). At the current rate of disappearance, it is expected that the Arctic seas will experience almost completely ice free summers by the end of this century.
Figure 3: Summer minimum Arctic sea ice extent from 1979-2005. (IPCC4)
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Glaciers
The retreat of mountain glaciers is among one of the most visible effects of climate change that we are able to observe today (see Figure 4), although instrumental measurement of such retreat is difficult due to the difficulty in accessing most glaciers and the expense involved in such studies.
Glaciers provide an important fresh water source for many parts of the world. A loss of mountain glaciers can impact fresh water availability for many, including parts of Western Canada.
Melting glaciers are an important contributing factor to sea level rise. As the climate warms, glaciers retreat at an accelerated rate, thus compounding the problem of rising sea levels.
Figure 4: McCarty Glacier, Alaska. The McCarty Glacier in Alaska as observed in 1909 and in 2004. (3)
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Permafrost
Permafrost is the layer of soil or rock that remains at below freezing (0°C) throughout the year. Permafrost is found at higher latitudes, where average surface temperatures are low enough to support the persistence of this frozen layer.
Because permafrost is dependent on surface temperatures, warming in the high latitudes greatly affects permafrost stability (see Figure 5). Thawing permafrost has grave implications for the regions affected, from the collapse of structures built on the permafrost to vegetation changes. As a result, thawing permafrost greatly affects all those who inhabit these regions, from people to animals to vegetation.
Figure 5: The sensitivity of Canadian permafrost regions to climate warming. (4)
