Planetary Albedo

As shown in the header image of clouds over the tropical Atlantic, clouds powerfully reflect solar radiation. Of the approximately 340 Wm-2 of solar radiation that is incident on the top of the atmosphere, 100 Wm-2 is reflected. Of this 70 Wm-2 is reflected by clouds. Because some clouds form over bright surfaces, in the absence of clouds the planet would still reflect roughly 50 Wm-2 of the incident solar radiation. So clouds have an albedo effect of 50-70 Wm-2, depending on how you count. In contrast the effect of doubling carbon dioxide is commensurate with a change in the radiative forcing of about 3.8 Wm-2. Which is to say that small changes in the planetary albedo can have very large implications for climate. So understanding what controls the planetary albedo, principally clouds, but also the distribution of sea-ice or the character of the land surface, is paramount to understanding the behavior of the Earth system.

To address this question we have launched an initiative within our department focused on the questions related to the control and stability of the planetary albedo. Specific questions we wish to answer include:

  • What determines the planetary albedo, and how different could it be?
  • Is the hemispheric symmetry in the net amount of reflected solar radiation an accident?
  • How does the planet respond to changes in planetary albedo?
  • What determines the distribution of snow and ice, including sea-ice?
  • Why is the ITCZ north of the equator?

Much of the research centered around the planetary albedo initiative is centered in the climate dynamics group lead by Juergen Bader and Thorsten Mauritsen. However,  the questions it touches on leverages a number of other research topics within the department, such as controls on hydrology, the effect of geoengineering solar radiation which is being explored in the IMPLICC project, or the question of what determines cloud feedbacks, which is being explored in the EU funded EUCLIPSE project. But they also initiate research in their own right, as explored in related pages.

Contact: Bjorn Stevens & Juergen Bader