Without a doubt, the most common topic of conversation among inhabitants of the world is the weather. In a broader sense, this is quite reasonable. Collapses of many ancient societies can be attributed to rapid shifts in climate. The blame on social, economic and political forces must often be considered secondary causes. Sudden dramatic climate changes have always struck human societies and they will struck again. They are an inevitable part of human condition.
The climate is a typical self-organizing system and as such extremely sensitive for subtle triggering conditions not possible to define and influence. A microscopically, often random adjustment of an initial value can trigger violent changes of a final value in a whole weather system (see “The butterfly effect” on p. 74). To predict when abrupt climate changes will occur and what form it will take is seldom possible. Major climate changes that suddenly occur often persists for a long time, even thousands of years. A typical example is Sahara, which was converted about 5000 years ago from a green landscape with lakes, to the burning, sandy desert it is today. The visible course of events is a gradual change in temperature or other physical conditions which push the situation towards an invisible threshold. When this is crossed, the climate suddenly changes to a new state and usually stays there for a long time.
Today, human induced increases in atmospheric concentration of greenhouse gases is a likely cause for a general global warming. The predicted average rise in global temperature is estimated to reach 4-5 degrees C in the next 100 years. This warming will most likely push the earth’s climate faster towards a point of no return where sudden shifts into new, radically different conditions occur. Climate researchers suggest that greenhouse-induced warming will increase rainfalls overall in connection with more severe storms and flooding. These phenomena are, however, not expected to offset the drought on other places. Also, already cold places will paradoxically suffer from more cold.
Actual climate models suggest greater summertime drying with a rising global temperature. Mild drought will worsen and persist for the coming decades. The big grain belts will suffer and some plant areas will die, putting less water back into the air by evaporation. Thereby more plants die with further diminishing rainfall and a wicked circle is established.
The greenhouse effect is also strengthed by other human measures. Cropland has replaced forests, thereby changing how much sunlight the land reflects. Too much water has been pumped out of the ground, changing the amount of water carried by rivers into the oceans. Trace gases and particulates in the atmosphere has increased, modifying the characteristics of clouds, rainfall, etc.
Much knowledge about long time changes in climate has been generated by ice cores extracted from Greenland’s inland ice in a big research project about 15 years ago (Alley & Bender 1998). Specimen extracted from ice rods up to three kilometres long has given climate records from the past 110000 years. They are still investigated but clearly reveals wild fluctuations in climate like 10 degrees C in a mere decade. The records show more than 20 such sudden warming episodes.
Trapped dust and methane in old air bubbles residing in the ice cores give details of climate changes. With additional cues from high mountain glaciers, the thickness of tree rings, and the types of pollen and shells preserved in ancient mud at the bottom of lakes, it is possible to draw secure conclusions.
The existing system of ocean currents that strongly influence climate in the world and bring warmth to Europe, is called the North Atlantic conveyor belt. If global warming continues, many climatologists fear that large quantities of fresh water from frozen northern landmasses and Greenland will obstruct the conveyor. Normally, the sinking water drives the conveyor belt which warms the north and cools the south. A slowdown of the currents should cool the North Atlantic region even if global temperature continue to rise. Then winter becomes harsher in both Europe and North America and agriculture suffers. Central Asia gets drier and most of the regions of the Southern hemisphere become much warmer.
As one of the main regulatory phenomena which makes life possible on earth, climate is dependent on thousands of feedback and response mechanisms. Their existence and cooperation are still only partially understood. Further aspects on climate as a selforganizing system has already been mentioned in this book. See page 140 about the Gaia hypothesis.
Source: Skyttner Lars (2006), General Systems Theory: Problems, Perspectives, Practice, Wspc, 2nd Edition.