How does a reductionist such as myself teach about such a holistic, systems-based topic as climate change?
1) The Sun heats the Earth with a mixture of visible and invisible radiation.
2) The Earth radiates that thermal energy back to space, reaching a balance called thermal equilibrium. Energy in equals energy out.
3) Because the Earth is cooler than the Sun, the radiation signature of the Earth is much cooler than that of the Sun. The Earth radiates in the infrared.
4) Some gases in the atmosphere that are transparent to visible light (carbon dioxide, water vapor, methane, and others) are not transparent to infrared.
5) The infrared radiated by the Earth has a chance of being captured by these gases. Some will be re-radiated back into space, but some will be re-radiated back toward the Earth.
6) The part that is re-radiated back to Earth drives up our thermal equilibrium temperature.
7) The more of these gases in the atmosphere, the greater the chance of any bit of infrared energy being captured and sent back to Earth.
Now we are prepared to talk about the complex ways that systems work together. Water vapor is a more powerful greenhouse gas than carbon dioxide, but you can only get so much water vapor to stay in the air. It is temperature-dependent, and so the water vapor tends to cycle. Water vapor levels can’t runaway, unless temperature does so first. But there is no similar limit on carbon dioxide in the air. Therefore, a little increase in temperature due to carbon dioxide can lead to more water vapor, leading to higher temperatures still. Carbon dioxide is the trigger.
Carbon dioxide cycles naturally. Trees and other plants eat it, combining it with the hydrogen in water to make sugar. They release oxygen as a waste gas in the process. Plants of course use some of this sugar for their own needs, so really the sugar is more of a banking system for the plant, and some of the carbon dioxide will be released by the plant when it uses the energy in the sugar for life processes. However, plants take in more carbon dioxide than they release.
We eat the sugars made by the plants. We combine them with the waste oxygen, producing once again water and carbon dioxide. So eating, burning, or otherwise using sugars from plants doesn’t imbalance the carbon dioxide, since it came from the air quite recently. It’s ok to breathe!
But remember that trees and other plants are carbon sinks. They take in more carbon dioxide than they release, unless they are eaten. But not all trees are eaten. Some change to coal.
The coal in the ground is the result of millions of years’ worth of carbon sinks. These trees and other plants stored up carbon, ton after ton after ton. They fell into swamps and weren’t eaten by anything. Instead, the material changed. The hydrogen and oxygen were slowly squeezed out, leaving nothing but carbon behind. That carbon is full of energy, the energy stored by the plants in the first place. When we burn that coal, we’re releasing ancient sunlight. But we’re also releasing carbon dioxide into the air that had been buried for hundreds of millions of years. The Earth can’t absorb so much carbon so quickly.
Climate change is always happening, and there’s no reason to suspect that the Earth will continue to have a climate amenable to our species (and particularly our civilization) for any amount of time. However, we are driving the climate by pumping ancient carbon dioxide back into the atmosphere. It’s as if we’re driving toward a cliff with our foot on the accelerator. Yes, it may be true that the cliff face is slowly eroding away, anyhow, so even if we stand still the cliff will eventually erode away from below us. But driving fast toward the cliff doesn’t in any way help!
The Earth may well adjust to this extra carbon dioxide. After all, it was carbon dioxide once before. The levels of carbon dioxide in the atmosphere have changed over time, and will continue to change. Global warming may drastically change the Earth, and the change will likely drive many species to extinction. But species are always going extinct as climate changes. Life, though it may look very different, will adapt. Something will survive.
But can we? That’s the real question. As coastlines flood and agricultural patterns change, can our civilization survive rapid climate change? It’s an experiment we’ve never run before. Note that it will happen, eventually, no matter what we do. Climate will change, whether we drive it or not. So really there are at least two things we have to do.
1) Take our foot off the accelerator. Carbon dioxide in the atmosphere will increase global temperatures. How much? Nobody really knows. Maybe we’ll get lucky and maybe we won’t. But isn’t it silly to keep driving?
2) Learn, learn, learn. The Earth (that good mother) will kill us. Eventually. Volcanic activity. The next ice age. Even an asteroid impact. Climate cannot and will not stay just where we humans want it to. If we don’t learn about the Earth and all that can and has gone wrong, we are doomed. We have to keep learning.
But why must we survive? What’s so special about our one species? We are special. We are different. We are worth more than cows or chimpanzees or (yes, I have to say it) even sea turtles. Because we can learn. Because we can experience the wonder of this universe that created us. We are a way for the universe to know itself.