clouds – not just for make believe
If someone mentions clouds to you, first thing that comes to your mind might be a fluffy, cartoony wisp in the sky, or childhood memories of gazing up into the mid-afternoon sky and imagining each cloud was some sort of object. Chances are that clouds being involved in climate change never really crossed your mind, but scientific studies show that they actually might be.
Elementary school science shows that certain colors reflect certain light. For example, red surfaces reflect red light and absorb every other color. The same goes for most other colors, but black and white are a bit different. The color black reflects no light, and the color white reflects all visible light. When visible light hits the ground or water, it reemits as infrared light. Well since clouds are white and reflect all visible light, they prevent a lot of heat being contributed to global warming.
So clouds reflect and block light; this means that in theory they would cool the earth. Whats the catch? Well the catch is that certain clouds reflect light and certain clouds actually trap heat. Clouds that are higher up tend to allow more light to hit the earth and also traps more heat than lower clouds. Heres a diagram that shows the effects of high and low clouds:
So in theory, since high clouds warm the earth, any anthropogenic warming that creates more high clouds will make global warming much worse. This is what we call a positive feedback loop. And the same works for low clouds. Since they have a cooling effect on the earth, then in theory, if anthropogenic warming created more low clouds then it would diminish the effects of global warming. We call this a negative feedback. Studies show some pretty concrete evidence regarding high and low clouds and how they affect climate, but there is still quite a bit of uncertainty about what kinds of clouds would be created as a result of anthropogenic warming. Climate scientist Chris Colose understands just this:
Unfortunately, the fact that clouds cool the planet on average tells us nothing about how cloud properties might change in a new climate. Suppose for example that the coverage of high clouds increased in a global warming scenario, while low clouds didn’t change at all. Because high clouds have a warming influence, one would expect this effect to amplify any warming that is caused by carbon dioxide or other human activities. This is an example of a positive feedback loop, but unfortunately we have very little understanding of cloud physics in a warming world. If the coverage of low clouds increased and reflected more sunlight, this would be a negative feedback, and would tend to mitigate the effects of human activities. Because of this uncertainty however, we can’t say with high confidence whether doubling the CO2 in our atmosphere will warm the planet by 3.5 degrees Fahrenheit or 8 degrees Fahrenheit…
This uncertainty creates 2 possibilites: Either anthropogenic warming creates a positive feedback loop with clouds and something should be done about it now or it creates a negative feedback where not so extreme measures must be taken. This uncertainty makes the job of a policymaker so much harder. I don’t really know the specifics, but one would expect that depending on the type of feedback created by the clouds, different actions must be taken.
What do you think should be done about it?