There’s been some buzz about the relationship between clouds and climate recently, prompting Andrew Revkin of the New York Times’ Dot Earth blog to get his panties in a twist about the “…over-interpretation of a couple of [scientific] papers…”
What gives? I wanted to know too, so I’ve done a bit – ok, a lot – of research and this is what I can tell you: The heart of the discussion is not whether there is a cloud-climate connection (that’s clear), but rather over what that relationship behaves like. There are at least three possible theories, but before we get to those, let’s review some important background concepts.
Gimme the Basics First
First, scientists think of air as units of volume called air masses. Each air mass is identified by its temperature and moisture content. Clouds are basically wet air masses that form when rising air masses expand and cool, causing the moisture in the air to condense. You can see the process in action yourself just by exhaling outside on a cool morning. The Center for Multiscale Modeling of Atmospheric Processes has a webpage to answer your other questions about clouds.
Earth’s Energy Budget
Energy from the Sun is essential for life on Earth. Let’s pretend the Earth has an “energy budget” where solar energy is like money, absorption is like a deposit, reflection is like a transfer, and radiation is like a withdrawal. It’s not a perfect analogy, but it’ll work for starters: Most of the incoming solar energy (money) is absorbed by (deposited into) the ocean and earth surface, but some is absorbed or reflected (transferred) by the atmosphere and clouds. Most of the outgoing energy is radiated (withdrawn) to space from the atmosphere and clouds. The figure to the right illustrates this process.
The Greenhouse Effect
Thanks to the greenhouse effect, our planet is warm enough to live on. The greenhouse effect occurs within the earth’s energy budget when some of the heat radiating (withdrawing… remember our budget analogy from above?) from the ocean and earth surface is reflected (transferred) back to Earth by greenhouse gases in the atmosphere. Greenhouse gases include carbon dioxide, methane, and water vapor. This National Geographic interactive website entertains the concept.
Climate change is occurring largely because humans are adding more greenhouse gases to the atmosphere. More greenhouse gases in the atmosphere means more heat reflected back to earth and warmer temperatures. Warmer temperatures might sound pretty good to your right now (especially if you live in Minnesota and could see your breath this morning as you walked to school or work), but it’s not. Why? Check out NASA’s really great website on the effects of climate change.
Alright, already. What’s the climate-cloud relationship?
From what I can tell, there are three possible theories about the climate-cloud relationship:
So which is it? Probably NOT Theory #1. Maybe Theory #2… or maybe it’s Theory #3? Scientists aren’t quite sure yet, so neither am I, but the evidence is stacking against Theory #1 leaving two possible options. The next big question seems to be surrounding the size of the effects of Theory #2 and Theory #3.
Using what you just read about cloud formation, the earth’s energy budget, greenhouse gases, and climate change (Woah. You just learned a lot!), what do you think? What’s the climate-cloud relationship?
If you want, you can read more about what scientists are saying about the climate-cloud relationship here: