Sunday, May 15, 2022

A Sankey diagram* of the Albedo Effect

It’s complicated
Watercolour, crayon and marker
©2022 Charlene Brown

Albedo, or degree of whiteness, determines the fraction of light that is reflected by a body or surface, and the complementary fraction that is absorbed. Albedo is a simple concept that plays a complicated role in climate change, especially in the Arctic.

Sea ice covered with snow reflects as much as 85% of the sunlight that strikes it, absorbing only 15% of the heat. Whereas deep blue open water can absorb as much as 90% of the sun’s light and heat. The heating effect of climate change is compounded over the years as melting results in more open water and longer ice-free periods.  Melted ice is replaced with thinner ice, resulting in an earlier thaw the following year.

A similar compounded effect has been observed on land in the Arctic, where the length of the snow-free period each year will have an effect on the amount of time that the land is absorbing and holding heat, and subsequent speeding up of the spring thaw.  In addition to this, the lower albedo of bare land varies with the darkness of the vegetation.  Generally lighter deciduous vegetation will reflect more sunlight and absorb less than evergreen trees and shrubs.

An unexpected phenomenon, a shift in vegetation from conifer to deciduous ground cover, has been observed in the taiga of northern Canada by measuring the albedo of the area over a period of years. Last September, I wrote about the possibility that this increased reflectivity of the land surface will exert a negative radiative effect, or cooling, on the climate. 

 * Sankey flow diagrams feature directed flow lines the widths of which are proportional to the size or intensity of whatever is being measured, in this case incident and reflected sunlight.