A. Permafrost is any ground that remains completely frozen—at or below 0°C (32°F)—for at least two consecutive years. It is a vast, frozen layer of soil, rock, and organic matter found in polar regions and at high altitudes, covering nearly a quarter of the land area of the Northern Hemisphere. This frozen ground acts like a massive natural freezer, storing vast amounts of ancient, un-decomposed organic material. However, as global temperatures rise due to climate change, this once-permanently frozen ground is beginning to thaw.
B. The thawing of permafrost has profound and alarming consequences for both the local and global environment. Locally, as the ice-rich ground thaws, it can become unstable and collapse, a process known as thermokarst. This can damage infrastructure like buildings, roads, and pipelines built on top of it, and dramatically alter the landscape. It also disrupts ecosystems that are adapted to the frozen conditions.
C. On a global scale, the most significant threat is the release of greenhouse gases. The organic matter trapped in the permafrost—the remains of plants and animals that have been frozen for millennia—begins to decompose as the ground thaws. This decomposition process, carried out by microbes, releases massive quantities of carbon dioxide and methane into the atmosphere. Methane is a particularly potent greenhouse gas, with a much stronger warming effect than CO2 in the short term.
D. This release of greenhouse gases creates a dangerous feedback loop. The gases released from the thawing permafrost contribute to further global warming, which in turn causes more permafrost to thaw, releasing even more gases. This "permafrost carbon feedback" has the potential to significantly accelerate the pace of climate change. Understanding the rate and extent of permafrost thaw is now a critical area of climate science, as it represents a major tipping point in the Earth''s climate system.
IELTS Practice Tests Practice Test / Part 1 #176
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