Permafrost contains nearly twice the amount of carbon (approx. 1,000 billion metric tons) in the atmosphere.
Permafrost is the layer of soil that remains permanently frozen at or below 0 ºC, for a minimum of two consecutive years. Most permafrost regions usually occur in higher latitudes (areas closer to the North and South Pole) and comprise 24% of the total exposed area of land in the northern hemisphere. Although they are primarily found in higher elevations, permafrost regions are also found in alpine regions in lower latitudes.
The United Nations Environment Programme (UNEP) states that the permafrost regions are divided into different zones, depending on the amount of permafrost present below each land. Continuous permafrost zones are those areas of land which are almost entirely underlain by permafrost; discontinuous zones have underlying permafrost in 50-90% of the total area of land; and sporadic permafrost zones contain 10-50% of the same.
Now, with the rapid decline of the available permafrost cover, it is essential to know the reason behind it, and its consequent effect on climate and the ecosystem as a whole. Although no research has provided a conclusive report stating the exact cause of melting, various groups of scientists have postulated different possibilities that attribute to all melting regions. Before we discuss the causes that may be responsible for the melting of permafrost, let's get to know some of the essential factors that govern the existence of permafrost.
Factors Controlling the Permafrost
The surface layer of permafrost is called the active layer, which thaws every year during summer, and freezes over again during winter. It is in this layer that vegetation usually grows, where the organic matter of dead plants and animals is preserved, owing to annual refreezing.
The temperature of air plays a major role in the distribution of permafrost in any region. Any location having an annual mean temperature below 0 ºC, has the potential to help in developing permafrost. However, even the regions—depending on the amount of snowfall and other temperature conditions—with an average annual air temperature close to 2 ºC, have reported the presence of permafrost.
The ground temperature is highly regulated by the physical and chemical characteristics of snow, sunlight, and the amount of live vegetation present above the permafrost. The nature of the ground directly affects the nature of permafrost.
Surficial vegetation present in the active layer often helps in keeping the permafrost intact. According to Shur and Jorgensen (2007), in case of discontinuous permafrost, the shade that this vegetation offers is vital for the existence of permafrost, since it reduces the amount of sunlight that reaches the soil, thus, resulting in shallower active layers.
So, What Causes Permafrost to Melt?
Now that is a moot point; scientists have deliberated on several permutations and combinations as to what exactly is the cause. Since research is still underway, no concrete evidence or solution has been put forth so far.
After studying the active layers of different areas in several countries, it has been found out that no conclusive measurements were obtained. In some areas, the active layers had diminished to a great extent, whereas in others, there was no significant change.
Reports state that a rise in air temperature has resulted in warming up the ground, which has directly influenced the melting of discontinuous permafrost regions; especially the ones in Russia (Oberman, 2008; Romanovsky et al., 2010b).
While global warming is caused by a large amount of human contribution to the level of greenhouse gases, the consequent melting of glaciers and polar ice is definitely to be blamed for permafrost melting. Recent studies have suggested that in areas of glaciers and ice, there is a possibility for other causes. Hence, whether to blame climate change alone for the current thawing is the million-dollar question.
Along with ice sheets and glaciers, ground ice dominates the Arctic and Antarctic landscape. This ice mixes with the soil of active layers above the permafrost, incorporating a dark color. Thus, the sunlight that reaches the ground does not get reflected, and instead of bouncing back, it is absorbed by the surface layer that has mixed with the soil. The dark surface absorbs large amounts of solar radiation, thereby, insulating the underlying layers and causing them to melt.
Today, scientists are yet to reach a common understanding as to what is the real problem. Having more questions than answers in this particular area of study, they probably have a long way to go before they find a solution. But one thing is certain—even if there are additional factors that contribute to the melting of permafrost, the eventual outcome is definitely not going to be pretty.