Question

Explain these two apparent paradoxes associated with polar and subarctic climates. a. Although generally associated with small precipitation totals, these climates are classified as humid and not dry. b. Although polar regions experience extended periods of almost perpetual sunlight in the summer, temperatures remain cool.

Short answer

Polar climates are humid due to low evaporation, and their cool temperatures persist despite long sunlight due to low sun angles and high albedo.

Step-by-step solution

Understanding Arctic Humidity

The first paradox is understanding why polar and subarctic climates are classified as humid even though they have small precipitation totals. This classification arises because these areas have low rates of evaporation due to their cold temperatures. As a result, the small amount of precipitation that does occur is retained in the environment, maintaining sufficient soil moisture to qualify as humid.

Evaporation vs Precipitation Balance

A dry climate is typically characterized by higher evaporation rates than precipitation. In polar climates, even though the precipitation is minimal, the very low temperatures severely limit evaporation. This means that the water from precipitation is generally not lost quickly, contrasting with dry climates where evaporation exceeds precipitation.

Analyzing Polar Temperature and Sunlight

The second paradox is understanding why, despite the extended daylight hours in polar regions during the summer, temperatures remain cool. This is because the sun's angle is much lower in the sky, which means that the solar energy is spread over a larger area and is less intense. The high albedo of ice and snow surfaces also reflects a significant amount of solar radiation back into space, further limiting warming.

Sun Angle and Energy Intensity

In higher latitudes, the sun never rises very high above the horizon, even in full summer daylight. Thus, the solar energy received per unit area is significantly less than in lower latitudes. Despite increased daylight duration, the overall energy input remains low, keeping temperatures cool.

Reflectance and Surface Albedo

Polar regions are largely covered by ice and snow, which have a high albedo. This means that they reflect most of the incoming solar radiation rather than absorbing it. Consequently, despite prolonged exposure to sunlight, much of the energy doesn't contribute to warming the surface, maintaining low temperatures.

Key concepts

Subarctic Climate

Subarctic climates, found primarily in the high Northern Hemisphere, are characterized by cold, long winters and brief, mild summers. These regions are marked by vast swathes of coniferous forests and are subject to extreme seasonal temperature variations. Although subarctic areas receive low precipitation compared to temperate zones, they are still considered humid. Contrary to what one may expect, subarctic climates are not categorized as dry environments. This discrepancy arises because the cold temperatures significantly reduce evaporation rates. Thus, even minimal precipitation sustains the moisture level in the soil, which helps maintain these areas as humid rather than dry zones. Understanding this peculiar classification is crucial, as it underpins the dynamics of subarctic ecosystems.

Evaporation vs Precipitation

In climate science, the interaction between evaporation and precipitation is vital in characterizing climate zones. Dry climates are those where evaporation outpaces precipitation. However, in polar and subarctic climates, this is not the case. These regions experience low amounts of rainfall or snow. Yet, due to the consistently low temperatures, evaporation is remarkably limited. This means that the moisture from the little precipitation received tends to stay in the environment longer, helping classify these regions as humid. The water balance in these climates illustrates why they are distinct from typically arid regions, offering essential insights into their ecological characteristics.

Solar Radiation

Solar radiation is a key player in determining climatic conditions in different regions. In polar areas, though daylight extends for long hours during summer, the low sun angle results in diffuse energy distribution. This means that the same solar energy span covers a larger surface area, reducing its intensity. Moreover, the sunlight must travel through more of the Earth's atmosphere, which further weakens its power by reflecting some of it away before reaching the surface. This combination of factors results in cooler temperatures, despite prolonged exposure to sunlight during polar summers. Understanding this paradoxical effect of solar radiation is fundamental to grasping why polar climates do not warm significantly during their extended summer days.

Surface Albedo

Surface albedo refers to the reflectivity of a surface. Regions covered in ice and snow, such as polar regions, possess a high albedo. This high reflectivity causes a significant portion of incoming solar radiation to bounce back into space. As a result, even when these regions receive sunlight for longer periods during summer, very little of it is absorbed, and thus minimal warming occurs. The reflective properties of snow and ice deflect energy that could otherwise contribute to warming the surface and atmosphere, maintaining low ambient temperatures. Grasping the impact of surface albedo is crucial in understanding the temperature dynamics of polar climates and their resilience to solar energy influx.