The Implications of a Chaotic Climate
Climate is the average of our weather. Our climate is variable. According to Jose Rial "The Earth's climate system is highly nonlinear: inputs and outputs are not proportional, change is often episodic and abrupt, rather than slow and gradual, and multiple equilibria are the norm." (Rial, et al,11) The Earth is a rather fragile system, meaning that the range of temperature to maintain a habitable climate is very small. There have been fluctuations that have resulted in the various Ice Ages and there is a question as to whether these are the result of the Milankovitch cycles of the changing motion of the Earth relative to the sun. Although there is a high correlation, it is possible that the chaotic climate has actually magnified these and other events. If climate is highly chaotic then there is the possibility of multiple attractors and the climate could switch from one attractor to another. If this is a possibility then we have to be very careful about forcing our climate into another regime. A chaotic system stays around a value unless it is given enough of a push and then it can switch to another average value. It is possible that the stress of drastically rising temperatures could be a force that results in just such a change. The climate that we now have is suited for human habitability and if there was a change in climate it is likely that the climate would be less habitable or totally uninhabitable. So let us consider the evidence that the climate is chaotic.
Climatologists have created global computer models for the long-term behavior of the Earth's atmosphere and oceans. James Gleick indicates that the climatologists "have known for several years that their models allow at least one dramatically different equilibrium. During the entire geological past, this alternative climate has never existed, but it could be an equally valid solution to the system of equations governing the Earth." (Gleick, 170) This is known as the White Earth climate because the Earth is frozen over and the high albedo of the ice would result in very low temperatures. According to Gleick the computer models have a strong tendency to fall into the White Earth equilibrium and many climatologist wonder why it has not happened. Possibly it is just chance but in these scenarios it takes a large amount of energy to force the system into another climate. Is it possible that global warming is a sufficiently large push? According to Ian Stewart, "Indeed there is a good case for identifying 'climate' with 'attractor', and if we do then what we are discussing now is climate change. And then it is not the flap of a butterfly's wing that should concern us, but the massive build-up of human-made greenhouse gases." (Stewart, 250) The possibility of global warming changing our climate is a very real concern.
Lorentz also introduced the concept of "almost-intransivity" in which a system fluctuates around a given average for a period of time but unpredictably switches to another average value. Many climate models are susceptible to "almost-intransivity." Gleick suggests that this might explain why the Earth has drifted in and out of Ice Ages and that "The Ice Ages may simply be a byproduct of chaos."
Another example of a possible consequence of the chaotic nature of the climate has to do with the Thermohaline circulation, which is the circulation of the oceans including the Gulf Stream. The evaporation of the ocean results in a cooling of the water and a higher concentration of salt. Since cold water is denser than warm water as a result of its thermal properties, and salt water is denser than fresh water, the water sinks. This acts as a huge pump for the ocean and results in a "conveyor belt" across the globe. A drastic rise in global temperatures results in the melting of glaciers in the North, which is fresh water. This reduces the salinity and thus the density of the cold water reducing the water that sinks in the North Atlantic which could shut down the global pump. It is likely that in the past this stopped the circulation of water (Karl and Trentberth, 1721-2). The Gulf Stream is essential for the warming air currents that rise the temperature of much of Europe and the stoppage of the Gulf Stream resulted in Europe going into an ice age for hundreds of years. It is possible that the initial temperature increase was not sufficient to have this effect of melting the glaciers sufficiently, but that the chaotic nature of the climate magnified the effect. This chaotic event has occurred often throughout the Earth's history. The change from warm to much colder and longer intervals were always extremely rapid. Chivalet indicates that "The climate during the last glaciation was bistable. The system had a chaotic behavior, and alternates between two very different states of equilibrium. Both states and the abrupt changes occurring between them seem to have been strongly controlled by drastic changes in the thermohaline ocean circulation." (Chivalet, 58) The projected temperature increases by current climate models appear to be sufficient to once again stop the thermohaline circulation and send us into an unpredictable global climate.
John Houghton suggests that the climate is not strongly chaotic and that like the Milankovitch forcing, "the increases in greenhouse gases will also result in a largely predictable response." (Houghton, 1372) However, taking the stoppage of the thermohaline circulation into consideration, the changes in climate hardly seem predictable.
There is the possibility that our current rate of production of greenhouse gases could possibly result in a catastrophic change in our climate. Certainly there is enough evidence that we should be cautious. In addition to the predictable and devastating affects that global warming is likely to have as the temperature rises there are also the much more unpredictable consequences of putting stress on a chaotic system. A possible consequence of our continued massive production of greenhouse gases is the change in our climate. Humankind and all life is dependent on our climate remaining habitable and given the fragile range in which life is possible we are forewarned. We must be cautious because we may be approaching a point of no return. We only have one place to live right now, so we had better resolve to take care of the Earth's environment and its climate. The cosmos is certainly indifferent to our plight and our fate may well be in our own hands.
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