If you’ve heard of climate change, you’ve probably heard of the
“tipping point.” But what does this mean? To
understand, you must first understand earth’s “positive
feedback” systems. Let me explain.
Major Positive Feedbacks
You’re all familiar with positive feedback mechanisms
whether you know it or not. Positive feedback is when a change in A leads to a
change in B. And the change in B leads to a further change in A, which further changes B. This goes back and forth as both A and B continuously reinforce
each other—a sort of snowball effect. Besides snowballs, earth has some positive
feedback systems with tremendous implications to the climate. Let’s take a look
at a few and discuss how initial small changes can rapidly get out of control
and send things down an undesirable path.
- Snow Cover – As sun hits earth, some light is absorbed and some is reflected. The pleasant climate we enjoy on earth is the result of a delicate balance between this incoming and outgoing energy. Snow and ice on earth play an important role in this energy balance, serving as the “mirrors” that reflect much of the sun’s energy. As greenhouse gases (GHGs) from human activity continue to warm the planet, however, these mirrors are decreasing in size. That is, snow and ice are melting. And these reflective white surfaces are being replaced with land and ocean, which absorb rather than reflect energy. This is where the dangerous positive feedback process kicks in. Replacing a reflective snowy surface with a heat-absorbing surface leads to more warming. With more warming, even more snow melts, leading to even more warming. The process goes on and on, the end result being higher and higher temperatures. It is a frightening path, yet one we’re already pushing forward.
- Water Vapor – The oceans have done us an enormous favor over the centuries by absorbing much of the GHG we’ve emitted to the air. As physics would have it, however, warm water isn’t as good a gas absorber as cold water. Therefore, as we warm the oceans, we reduce the capability of the oceans to help us. On a global scale, warmer oceans absorbing less GHG has quite an impact. The oceans play another important role. Warmer temperatures lead to the evaporation of more ocean water. Water vapor is even a more powerful GHG than carbon dioxide. So as we warm the oceans, we increase the heat trapping capacity of the atmosphere, and in turn warm the oceans further. Another self-perpetuating feedback loop in motion.
- Dying Forests – The rain forests represent an enormous source of stored carbon on earth. As warming temperatures lead to dying forests, however, dead plant matter decomposes and releasing this stored carbon to the air. Active deforestation is also contributing to this. Unfortunately, less forest means less carbon storage. This means more atmospheric carbon and higher temperatures. Higher temperatures lead to even greater forest death, and so on. The cycle continues, again racing us to the precious of a runaway effect.
- Methane & Permafrost – This is potentially the most alarming feedback of them all. Within the soils of the frozen tundra is an enormous quantity of organic matter—partially decomposed plants and other organisms. While frozen, these organics pose no threat to our climate. Were the tundra to melt, however, decomposition of this matter would release vast quantities of methane and carbon dioxide into the air. Methane is even a better heat trapper than carbon dioxide; twenty-one times better! It is estimated that enough carbon is stored in permafrost to more than triple the current level of carbon in the atmosphere. I hate to report that global warming has already caused permafrost in Alaska and elsewhere to begin thawing as many regions that were previously frozen year round now experience above freezing temperatures. Carbon in the tundra represents a dangerously large source of GHG that is best left in the ground.
The
Tipping Point
This brings us to the so called tipping point, or what is often
thought of as the point of no return. That is, the point beyond which humans will have
any real control over continued climate change. Right now, the main driver of global
warming is human activity. However, once we reach a certain point and unlock the carbon in the tundra, as well as propel many of these other positive feedback systems, humans will have little say in how much our climate warms. Our efforts will be of negligible importance. Releases of permafrost methane, a
shrinking of earth’s “mirrors,” and a more humid atmosphere are just a few of
the many processes that will secure the fate of our climate.
Triggering the permafrost to melt is probably the most frightening
scenario given the enormous reservoir of carbon waiting to enter the sky. A true tipping point will have been reached. We'll have unleashed the giant. Melting of the snow would then accelerate. Dying of the
forests would increase. The atmosphere would gain humidity only humidity. And all these processes would only accelerate each other, as positive feedbacks do. It’s a frightening
prospect to say the least, but a very real one. And only underscores the importance of current climate action efforts.
So when is the tipping point? It’s any scientist’s best guest. But evidence suggests it’s sometime soon, if we haven’t already reached it. We are playing with fire, as they say. We are quite literally conducting a global experiment.
So when is the tipping point? It’s any scientist’s best guest. But evidence suggests it’s sometime soon, if we haven’t already reached it. We are playing with fire, as they say. We are quite literally conducting a global experiment.
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Shahir Masri, Sc.D.
Environmental Health Scientist
