The polar circle is a geographic term for a circular line that marks the boundary of the polar regions on Earth. There are two polar circles: the Arctic Circle in the north and the Antarctic Circle in the south. These are two of the five major circles of latitude that divide the Earth into zones based on the angle of sunlight they receive throughout the year.

The polar circle is important because it defines the area where the Sun can remain continuously above or below the horizon for 24 hours at least once a year. This phenomenon is known as the polar day or the midnight sun in summer, and the polar night or the darkness in winter. The duration and intensity of these effects vary depending on how far north or south one is from the polar circle. For example, in Murmansk, Russia, which is three degrees above the Arctic Circle, the Sun does not rise for 40 days in midwinter.

The position of the polar circle is not fixed and depends on the Earth’s axial tilt, which changes slightly over time due to gravitational forces from the Moon and other planets. The current average tilt is about 23.4 degrees, which means that the polar circle is at about 66.6 degrees north or south of the equator. The polar circle is currently drifting northwards or southwards at a speed of about 14.5 meters per year.

The area north or south of the polar circle is called the frigid zone, and covers about 4% of Earth’s surface. It is mostly covered by ice and snow, and has a harsh climate with low temperatures and strong winds. The frigid zone is home to some unique plants and animals that have adapted to survive in these extreme conditions, such as polar bears, penguins, seals, mosses, and lichens. It is also inhabited by some human communities that belong to different cultures and traditions, such as the Inuit, Sami, Nenets, and Antarctic researchers.

The polar circle is a fascinating and important feature of our planet that affects its climate, ecology, and human history. By learning more about it, we can appreciate its beauty and significance.

Climate change is having a profound impact on the polar circle and its ecosystems. The polar regions are warming faster than any other area on Earth, with the Arctic ocean and air temperatures rising twice as much as elsewhere. The Greenland and Antarctic ice sheets are both losing net mass to the ocean, mostly through increased melting from the atmosphere and the ocean. This contributes to global sea level rise and alters ocean currents and salinity.

One of the most visible effects of climate change in the polar circle is the decline of sea ice, which covers less area and thickness than before. Sea ice is critical for many species that depend on it for hunting, resting, breeding, and migrating, such as polar bears, seals, walruses, penguins, and whales. Sea ice also reflects sunlight back to space, helping to cool the planet. When sea ice melts, it exposes more dark ocean water that absorbs more heat, creating a feedback loop that accelerates warming.

Another consequence of climate change in the polar circle is the shift of vegetation and animal ranges. As the climate becomes warmer and wetter, more woody plants are growing in areas that used to be dominated by tundra and grasses. This affects the food availability and quality for grazing animals such as reindeer, caribou, and muskoxen. Some animals are also moving northward or southward to find suitable habitats, such as fish stocks in the Barents Sea that are moving north at up to 160 kilometers per decade. This poses a challenge for commercial and subsistence fisheries that rely on these resources.

Climate change in the polar circle also has implications for human health and well-being. The melting of permafrost, which is frozen soil that contains organic matter and microbes, releases greenhouse gases such as carbon dioxide and methane into the atmosphere. It also destabilizes infrastructure such as roads, buildings, and pipelines that are built on top of it. The reduction of sea ice also exposes coastal communities to more storm surges and erosion. Moreover, the changes in the polar environment affect the culture and livelihoods of indigenous peoples who have lived there for generations.