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Picture a simple theoretical planet. Simpler.

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Simpler. Keep, keep going, keep--nope that's

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too far. That is just a dot. Not even trying. Ok,

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there. This is DaisyWorld, a place where only two things

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live: black daisies and white daisies.

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In the early days, the atmosphere of DaisyWorld

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is cooler and black daisies thrive in these cooler temperatures.

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The black daisy population does so well in fact

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that it absorbs more energy and begins the warm the little planet.

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But now it's too warm for black daisies, but it's just right for the white

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daisies to blossom and expand. And while the planet is covered with

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more and more white daisies, they begin to reflect more energy back

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into space. We call this amount of reflectance albedo. The more reflective

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the surface of the planet, the higher its albedo. We can think of it

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as a percentage of how much energy is coming in and then bouncing back out

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into space. For instance, the albedo of a perfect mirror would

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be one hundred percent. If we had a completely

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black surface the albedo would be zero percent.

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Or a waterworld, that could be twenty percent.

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Now the white daisies cool the planet again,

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and that makes it more favorable for black daisies to thrive once again.

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Now we're back to where we started. The black daisies have taken over

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but they'll warm up the planet, and then they'll die and the white daisies will grow

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but then they'll reflect more heat back out and then they'll die and on and on and on and back

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and forth.

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And over time, within a narrowly defined temperature range,

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DaisyWorld stays resilient and makes it possible for daisies to exist

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at all. Of course, this is a theoretical planet; there are no

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variables, like rotation, seasons,

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diseases,

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geography, or even humans.

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It does illustrate how a change in one environmental condition

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can cause a change in a second condition, which in turn, can change the first condition

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again. We call this a feedback loop.

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The DaisyWorld model is an example of a negative feedback

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loop because the initial changes to the climate are muted by the combination

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of black and white daisies. On Earth

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we can see this kind of negative feedback loop with clouds. Let's say

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increasing temperatures cause more surface evaporation, which cause more

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cloud formation, and clouds, much like our white daisies, have a

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higher albedo than the Earth's surface. Then the clouds will

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reflect more heat and cool the planet. When we look at snow

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and ice at the poles, which have a high albedo, we can see a positive

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feedback loop. When temperatures rise, the snow and ice

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melt, and so even more energy is absorbed by the water, and this

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continues to melt the snow and ice even further. With increasing climate change

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the natural reflectance of our icy poles dramatically declines.

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DaisyWorld is a much simpler place than our own planet,

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but it shows us that maintaining a population on Earth requires a

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delicate balance with the right organisms and the right range of

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environmental conditions.

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Beep, beep.

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