Albedo and Feedback

Picture a simple theoretical planet. Simpler, ok simpler, keep going. That’s too far, that is just a dot, you’re not even trying. Okay there. This is Daisy world, a place were only two things live, black daisies and white daisies. In the early days, the atmosphere of daisyworld is cooler and black daisies thrive in these cooler temperatures. The black daisy population does so well in fact that it absorbs more energy and begins to warm the little planet. But now it's too warm for black daisies but it's just right for the white daisies to blossom and expand. And while the planet is covered with more and more white daisies, they begin to reflect more energy back into space. We call this amount reflectance albedo. The more reflective the surface of the planet, the higher the albedo. We can think of it as a percentage of how much energy is coming in and then bouncing back out into space. For instance the albedo of a perfect mirror would be 100 percent. If we had a completely black surface, the albedo would be zero percent. Of a water world, that could be 20 percent. Now the white daisies cool the planet again and that makes it more favorable for black daisies to thrive once again. Now we're back to where we started. The black daisies have taken over but will warm up the planet and then all die and the white daisies will grow but then they’ll reflect more heat back out and then they'll die and on and on and on and back and forth. And overtime within a narrowly defined temperature range daisyworld stays resilient and makes it possible for daisies to exist at all.

Of course, this is a theoretical planet. There are no variables like rotation, seasons, diseases, geography, or even humans. It does illustrate how a change in one environmental condition can cause a change in a second condition, which in turn can change the first condition again. We call this a feedback loop. The Daisyworld model is an example the negative feedback loop because the initial changes to the climate are muted by the combination of black and white daisies. On Earth, we can see this kind of negative feedback loop with clouds. Let's say increasing temperatures cause more service evaporation, Which causes more cloud formation. And clouds, much like our white daisies, have a higher albedo than the earth's surface. Then, the clouds will reflect more heat and cool the planet. When we look at snow and ice at the poles, which have a high albedo, we can see a positive feedback loop. When temperatures rise the snow and ice melt and so even more energy is absorbed by the water and this continues to melt the snow and ice even further. With increasing climate change, the natural reflectance of our icy poles dramatically declines. Daisyworld is a much simpler place than our own planet, but it shows us that maintaining a population on earth requires a delicate balance with the right organisms and the right range of environmental conditions.