Category: Environment

“Some say the world will end in fire, some say in ice.”
– Robert Frost

Last month I wrote about positive feedback loops. Another name for these loops is “vicious circles”. Their end result is often very destructive since a positive feedback loop can run out of control quickly.
An example of a positive feedback loop we all know is a sound system that squeals when the volume is turned up too high. Another example is what is happening to the ice pack in Greenland and to many glaciers. Being light in color, snow and ice reflect most of the sun’s warmth. As the climate heats up, snow and ice melt exposing rock and soil underneath. Because of the darker color, they absorb more of the solar radiation which heats them up more, and so on.
In last month’s article I described six other positive feedback loops that all work to increase the planet’s temperature. Several involve the greenhouse gases, carbon dioxide and methane. The sky-rocketing level of CO2 is the result of human activity—from our profuse use of fossil fuels.
Thanks to careful monitoring since 1958, we know that the CO2 in the atmosphere has increased from 315 parts per million (ppm) to 380. The rate of increase of CO2 is even faster now than back in the 1950s. Furthermore, historic levels are significantly higher than any for the prior 650,000 years! How can we determine CO2 in the atmosphere from so long ago? Scientists measured the gas content of bubbles in Antarctic ice going back that far. Methane, 24 times as powerful in keeping in the sun’s heat, is also rising dramatically.
The planet’s temperature back in prehistory has also been estimated using isotopes of oxygen. If you compare a graph of those temperatures and a graph of CO2 concentrations, there is a strong correlation. It seems that the planet gets a fever whenever the CO2 level goes up! The greenhouse effect of CO2 (and methane) is the cause of this temperature rise.
Our time in the history of the earth is without precedent so no one can predict with certainty what the future will hold. Although our species has been around for a hundred thousand years, we have only been using fossil fuels in a big way for about 250 years. Never before has humanity faced the possibility that it has changed the planet’s climate so radically.
Some predictions made by scientists are frightening. One model suggests that the climate will change even more drastically when atmospheric CO2 reaches 500 ppm. At the current rate of increase this will happen before the year 2100. Negative feedback systems now functioning limit warming. For example, as trees burn and release CO2, the smoke shades and decreases heat absorption. At 500 ppm those systems will be totally overwhelmed and the temperature will rise even more rapidly. Quite simply, we will bake. The world as we know it will no longer exist.
The prospect in the short run is also terrifying. If the average temperature rises just five degrees Celsius (9 degrees Fahrenheit), most of the temperate parts of the planet will become desert. This might happen about 2050, according to preliminary information from the Intergovernmental Panel on Climate Change. Not only will the climate become hotter, precipitation will diminish through much of the world. The subarctic, currently too cold to grow much, will become the most productive area in this future. There will be much less agricultural land in this scenario, and the growing season will be short. The saddest part of this model is that this rise in temperature will prove fatal to many millions of people—perhaps even billions. They will starve to death.
Unless we change our course radically, the future looks frighteningly bleak. Fortunately I will be dead before the full consequences of global warming hit, but I cannot help but think of what will happen to my granddaughter—and millions of other youngsters. This calamity is largely a consequence of my generation and others of the 20th century. We reproduced faster than in any other era of human history. And we enjoyed the pleasures of fossil fuel to the hilt. Unfortunately it is not we who will suffer the consequences, but our offspring. Our iniquity will go beyond the third and fourth generations.
It may already be too late to prevent this climate hell, but that doesn’t mean that we shouldn’t try. Averting global climate change will be the subject of next month’s article.

© Richard Grossman MD, 2006

Feedback is essential for normal functioning. An example is if you lurch to the left while walking, your body senses this and compensates by tensing muscles to keep you upright. Another example is when it gets hot you sweat, which cools you off.
Most of these control loops that maintain normalcy are negative; if there is an error, the control mechanism acts to counteract that error. They are essential to every living being—and to our planet.
Although rare in nature, there are also positive feedback loops, which usually have bad consequences. A common example is a sound amplifying system that squeals. Here’s how that works.
The singer at a concert is quiet, so someone turns up the volume. The amplifier makes her voice louder, but the microphone also picks up sound from the speaker and amplifies it. At some critical point the noise from the speaker gets amplified more than the singer’s voice and there is a terrible high-pitched squeal. People slap their hands over their ears until someone turns down the volume.
Note that negative feedback is good, because it keeps things under control. Positive feedback is bad because it quickly gets out of hand, and can be thought of as a “vicious circle”.
The future may hold several destructive positive feedback loops leading to increased global warming. Their end result is that the warmer it gets, the warmer it will get.  Combined, these may cause such a profound effect on Earth’s climate that the planet becomes uninhabitable except for a relatively small portion of its surface.
Many loops involve increasing greenhouse gases. Like an actual greenhouse, these gases hold in the sun’s heat and keep it from escaping from the atmosphere. Carbon dioxide (CO2) has the highest concentration and is the best known. Although it sounds as though the greenhouse effect might not do very much to the climate, it can cause huge consequences. Other planets provide an example. Although further from the sun, Venus is a lot hotter than Mercury because of runaway greenhouse effect. Almost all scientists agree Earth’s climate is getting hotter. They also agree that the increase is due to human actions—primarily CO2 from using fossil fuels.
One positive feedback loop affecting the climate takes place in the arctic. Ice and snow reflect much of the sun’s heat back into space. As the climate heats up, the Greenland icecap, and other glaciers, melt. This exposes darker ground that absorbs more of the sun’s heat, causing more glacial melting, and so on.
One advantage (one might think) of less ice in the north is that more trees and plants could grow—and grow they do. The growth helps to absorb CO2, thus keeping down greenhouse gas concentrations. But it turns out that these boreal forests are darker than the bare ground, so they absorb more heat. Calculations suggest that the benefit on CO2 is offset by the effect of the darkness, unfortunately.
In addition to trees and plants keeping CO2 out of the atmosphere, the ocean absorbs a huge amount of this gas. Some is dissolved in water, and some is sucked up by the growth of algae. As the oceans heat up, both of these processes will diminish. Open a can of hot soda and it explodes; the CO2 won’t stay in solution. Algae don’t grow well in warmer water, either, so there’s more CO2 in the air.
During the sweltering summer of 2003 in Europe, scientists found that trees stopped growing. In fact, their metabolism released CO2 instead of fixing it. The heat also killed plants and animals, releasing more CO2 from the corpses. Tropical rainforests are called “the lungs of the planet” because they breathe in CO2 and exhale oxygen. They will suffer from increased heat—another cause of increased CO2.
Another greenhouse gas, methane, is twenty-four times more powerful than CO2 at trapping heat. In addition to the methane burped out by cows and generated by decay, there are billions of tons of it frozen in the arctic. Methane liberated by global warming will intensify the greenhouse effect.
It seems as though our use of fossil fuels has set into motion vicious cycles that will change the nature of our climate—and of our planet. A relatively small rise in temperature will make many areas of the planet barren and uninhabitable. Hurricane Katrina is an example of a cataclysmic weather event resulting from global warming. Next month I’ll write more about the effects of heating up our planet.

© Richard Grossman MD, 2006