A Positive Outlook

March 18, 2014 by Caroline Ailanthus 7 Comments

Positive feedback isn’t always good. In fact, in a scientific context, positive feedback is one of the things that keeps climate scientists up at night.

Feedback, in a scientific or engineering context, doesn’t mean compliments or criticism. Instead, it refers to any force that turns around and influences its own source. An oven with a thermostat contains a feedback loop, since rising temperature turns the oven burner off and falling temperature turns the oven burner back on. That is a negative feedback loop because the thermostat acts to say “no” to whichever direction the temperature is moving. The oven stays at a nice, even temperature this way, until your pumpkin bread is done and you turn the oven off.

Positive feedback, in contrast, never says no. It only says yes. Imagine an insane oven set to turn the burner on HIGHER when the temperature rises. A hot oven would only make a hotter oven and the whole thing would very quickly burn up. Not all positive feedback loops are bad—a child who feels encouraged by good grades and so studies even more is also experiencing positive feedback—but you can see how this sort of mad oven scenario would be a problem for the climate.

So strong is our association between the word “positive” and the word “good” that some otherwise very educated people sometimes get it wrong and say “negative feedback” when they mean “positive feedback.” But remember, “positive” basically just means “yes,” and “yes” is not always good.

Feedback loops are always part of our planet’s climate. Our planet maintains its temperature in much the same way that our bodies maintain ours, through a complex network of interacting feedback loops, including some limited positive loops. While it might be too much to attribute conscious intention to the planet, it’s important to realize that the Earth is not a passive system. The Earth is capable of doing things, like bodies can do things, so when we do something to the Earth, it doesn’t just react in a linear way like a bookshelf falling over. It responds, and we can’t easily predict what it will do.

The way the planet responds is through a shift in the pattern of feedback loops.  If something triggers a new positive feedback loop the world as we know it could change very suddenly.

Accurately modeling all the factors that could possibly impact our climate would require a computer as complex as the actual world. Not surprisingly, we don’t have one. So scientists use simplified computer models instead, models that are capable of generating predictions that are roughly accurate in a general way. The computers ignore a lot of the feedback loops we do have or could have, but at least they tell us what will happen if things keep going along as they are now.

That kind of simplified prediction should be enough. We can clearly see what climate change is, why it is happening, and the fact that we’re headed in a disastrous direction.  We should take these predictions as a warning and a motivation to all work together to stop adding greenhouse gases as soon as possible. But that isn’t what business leaders and policy makers are doing, for the most part.

Instead, when policy makers look to these predictions at all, they seem to see not a warning but a kind of budget. So, if the prediction says that X tons of greenhouses gases will cause Y disaster, they see that as permission to emit greenhouse gases up to X tons. And that is a problem because we already know that the prediction is an underestimation, maybe a gross underestimation. We know it doesn’t contain the feedback loops, the mad ovens suddenly turned on.

So here, for your edification, are some of these missing loops.

The Amazon rainforest sits under a rainy part of the global air circulation pattern, but the forest also makes itself rainy, rainier than the area would be without the forest. There are two mechanisms involved. First, the trees of the forest recycle much of the rainwater. Normally, of course, rainwater flows away to the sea. Rainforest trees, however, draw massive amounts of water up out of the soil and release it again through their leaves. There are so many trees massed together that a lot of the water never gets a chance to flow away. The same water keeps raining on the same land over and over again. Second, for water vapor to become rain, it must have particles of the right size to condense around. Spores, pollen, and plant debris from the rainforest provide ample condensation nuclei, again creating more rain right over the forest. Because of these two factors, the more rain there is, the more trees grow, and the more trees grow the more rain there is. That’s a mild positive feedback loop, one that we like because it is held in check by other factors.

But remove too many trees and the loop reverses direction; the fewer trees, the less rain, and the less rain, the fewer trees, because rainforest trees need a lot of water. This means that if deforestation progresses too far, the rainforest will begin to shrink ahead of the axes. Then even if logging stops entirely, and the forest would continue to shrink.

Fire adds another layer of feedback. Not only does fire, like logging, sometimes kill the trees that make the rain, but a drier forest burns more often. The faster the wheel spins, the faster it spins. Also, smoke from fires disrupts cloud formation, reducing rainfall, and making the forest more likely to burn. Forest fires themselves are not bad and even rainforests have always burned occasionally. The problem is that increased fires are one part of the looming complex of new positive feedback loops. If fires become too frequent, the forest will not have time to grow back during the interval.

Global warming stands to increase drought, and therefore fires, in the Amazon, even aside from drought caused by deforestation itself. Whether the recent droughts and fires in the Amazon were the result of global warming specifically is one of those misleading questions, like whether a single hurricane or typhoon is caused by global warming; climate change is a trend, and trends are only visible in multiple incidents. But we can expect more bad droughts (just like we can expect more hurricanes) if global warming continues.

And here is where the positive feedback loops get really scary.

The Amazon rainforest is, at present, a carbon storage facility. The weight of all those plants and animals is made out of carbon compounds that would otherwise be floating around the atmosphere. The Amazon also sends a lot of nutrients downstream and out into the Atlantic, where huge numbers of phytoplankton use those nutrients to grow like crazy. Those well-fertilized phytoplankton create a huge percentage of our planet’s oxygen and, in the process, sequester huge amounts of carbon. So, both directly and indirectly, the Amazon rainforest is slowing the progress of climate change. Deforestation, both through logging and, recently, through fire, is a major source of greenhouse gasses because it releases the carbon from storage and impairs the forest’s ability to soak the carbon back up again.

But we know that at some point, if the combined pressure of deforestation and drought continues, the forest will start to shrink. It will die back. And whether that die-back takes the form of dramatic forest fires or only a slowing in the growth of trees to the point where dead trees rot faster than new ones grow, the Amazon will stop being a carbon sink. It will become a carbon source, bleeding its substance uncontrollably off into the sky. And, with more greenhouse gasses to play with, climate change will get worse.

So, the more the planet warms, the faster trees will die and the faster trees die, the more the planet will warm.

We are facing the mad oven scenario, but all is not gloom and doom. In fact, despite having already committed ourselves to some amount of further warming, we still have time to make the future better by stopping our use of fossil fuels and our unsustainable deforestation now. We still have a chance. And as long as we are still capable of making things worse, we will also be capable of making things better. And we can make things better, if we collectively start treating the time we still have as an opportunity to change instead of as an opportunity to not change.

Climate change is a serious problem, but it isn’t, at bottom, a complicated problem. Or, at least the solution isn’t actually complex. Just turn the fossil-fuel-powered machines off. Find something else to do.