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  • Picture a simple theoretical planet. Simpler.

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

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

  • there. This is DaisyWorld, a place where 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 the 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 of reflectance albedo. The more reflective

  • the surface of the planet, the higher its 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 one hundred percent. If we had a completely

  • black surface the albedo would be zero percent.

  • Or a waterworld, that could be twenty 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 they'll warm up the planet, and then they'll 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 over time, 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 of a 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 surface evaporation, which cause 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.

  • Beep, beep.

Picture a simple theoretical planet. Simpler.

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B2 planet black loop feedback simpler reflect

NASA | This World Is Black and White

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    Bing-Je posted on 2013/12/13
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