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.