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The secret of global glacier retreat: How does it reveal surprising evidence of climate change?
The retreat of glaciers around the world since 1850 has become important evidence of climate change. The rapid disappearance of glaciers, especially in mountainous areas, is a clear sign of the rise in global temperatures since the late 19th century. Among them, the mountain glaciers in western North America, the glaciers in Asia, the Alps in central Europe, and even the glaciers in tropical and subtropical regions of South America and Africa have all become witnesses of this change. The sensitivity of glacier mass to climate change over time makes it an important indicator for observing climate change.
From 1993 to 2018, the total loss of glaciers worldwide reached 5500 gigatons, an average of 210 gigatons per year.
Excluding the outer glaciers of the ice sheets, 99% of the Earth's glacial ice is stored in the huge polar ice sheets. These glaciers are found in mountain ranges on every continent, with the exception of Australia itself, which has no glaciers. Typically, glaciers larger than 50,000 square kilometres (19,000 square miles) are called ice sheets, and they can be several kilometres thick, obscuring the underlying terrain. While the natural retreat of glaciers is normal at the end of ice ages, the current retreat is being accelerated by human-caused greenhouse gas emissions.
Since the Industrial Revolution, human activities have significantly increased the concentration of heat-diffusing greenhouse gases such as carbon dioxide in the air, causing the current global warming phenomenon. Human impact is considered the main driver of change in the cryosphere, of which glaciers are an important component. The mass balance of a glacier - the difference between the amount of snow condensing in its accumulation zone and the amount of ice lost in its ablation zone - is a key metric for assessing its health.
If the accumulation is less than the ablation, the glacier will retreat, otherwise it will advance.
Mid-latitude mountain ranges such as the Himalayas, Rockies, and Andes have seen a high rate of glacier loss. As glaciers melt, the impact on local water sources is becoming increasingly apparent, especially for residents in the Andes and the Himalayas, who will face a shortage of drinking water and irrigation in the future.
In addition, the retreat of glaciers directly contributes to rising sea levels. According to the Intergovernmental Panel on Climate Change (IPCC), the potential for sea level rise depends primarily on large-scale melting of the Greenland and Antarctic ice sheets. Melting in these areas could raise global sea levels by more than 70 meters.
If the polar ice caps melt completely, the world's oceans will rise by about 70 meters.
However, it cannot be ignored that glacier retreat has also had a significant impact on the ecological environment. Many freshwater fish species depend on cold water for their survival, and some species, such as salmon and cuttail trout, require these cold water environments to reproduce. As glacial water flows decrease, the survival of these fish will face great challenges.
Another impact observed is an increased risk of glacial lake outburst floods (GLOFs). As retreating glaciers form unstable terminal moraines, these moraines may collapse under the influence of earthquakes, landslides or avalanches, causing localized flooding hazards. Historically, this disaster has caused huge loss of life and property, especially in villages and towns located downstream of glacial lakes, which are at greatest risk.
Recent studies show that Europe's glaciers are retreating at an accelerated rate. For example, the Gross Allech glacier in Switzerland lost 2.8 kilometers between 1880 and 2009, and according to a 2009 University of Zurich report, glaciers in the Alps have shown an alarming retreat over the past few decades.
Two glaciers in the Alps are expected to disappear completely by the end of the 21st century.
Regarding the future state of glaciers, climate change experts say that almost all glaciers currently have a negative mass balance. If the climate does not change significantly in the next few decades, glaciers will likely continue to be consumed. This phenomenon not only affects local water resources, but will also affect human life.
Faced with the rapid retreat of glaciers around the world, how can we actively respond to the challenges of climate change?
