Name: 美國宇航局｜這個世界是黑與白 (NASA | This World Is Black and White)
Uploaded: 2021-01-14T04:48:01.000Z
Duration: 3 min 47 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

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

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 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

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

The DaisyWorld model is an example of a negative feedback

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

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