365 Days of Climate Awareness 6 - Albedo

365 Days of Climate Awareness

6 - Albedo

Albedo is the reflectivity of any given surface on the planet. The surface might be exposed ground, desert sand, open water, ice and snow. clouds, boreal or temperate or jungle forests, farmland, grassland, or otherwise. It's measured on a scale from 0 to 1, being a percentage of total incoming radiation, with 0 for a perfect blackbody (total absorption) to 1 (perfectly reflective).

Reflectivity of the planet plays a huge role in climate, with a number of different feedbacks. "Feedback" is when the output of a system then becomes input again to the same system. (Hendrix pioneered this musically, playing in front of the speakers on stage.) A positive feedback is one which causes the process to accelerate, making the system less stable. A negative feedback causes the process to slow down, making the system more stable again.

Concept of albedo.

Both positive and negative feedbacks occur within the climate system with respect to
warming, though the positive feedbacks greatly outweigh the negative. In one instance, increased temperature causes more evaporation around the world, leading to higher water vapor content within the atmosphere, increasing the atmosphere's insulative effect: a positive feedback. However, more water vapor produces more clouds, which are highly reflective--having albedos between 0.4 and 0.8--and are a negative feedback on warming. (Therefore increased water content in the atmosphere has a variable effect.)

Some decidedly positive feedbacks resulting from changes in albedo: loss of ice and snow (from 0.3 to 0.85 albedo), being replaced by open water (albedo <0.1), soil (0.5-0.35) or small vegetation (0.1-0.25). (This is one big reason why loss of glacier and sea ice are very important, ominous developments.) All the radiation not reflected is absorbed and warms what absorbs it.

Replacement of forest with grass or farmland--being aggressively pursued in Brazil--increases the amount of CO₂ in the atmosphere, since trees consume far more carbon dioxide than smaller plants, but increase the albedo (forest: 0.5-0.15, vs. farmland, 0.15-0.25), a negative feedback. In this case the increase in albedo--the negative feedback--is overwhelmed by the change in vegetation and decreased CO₂ consumption.

Tomorrow: carbon dioxide sources and sinks.

Be well!