There are a number of "tipping points", loosely defined as critical thresholds at which small human activities can result in large, uncontrollable, long-term climatic consequences. Not so long ago, the very thought of a tipping point seemed unreasonable, now they appear both real and near. We also have a tendency to believe that there is a smooth relationship between our actions and the environmental responses. We are accustomed to seeing graphs of either a straight line, or a curve. Tipping points, however, will most likely result in an abrupt or disjunctive response.
The most immediate tipping point appears to be the melting of Arctic summer sea ice, commonly projected to occur within the next 10 years. The Arctic summer sea ice has been melting at a rapidly increasing rate during the past couple of decades, with the actual amount typically exceeding the projections of the most recent climatic models. It is generally felt that a temperature increase of only a fraction of a degree (Centigrade) will result in a completely summer ice-free Arctic sea within the decade. A temperature increase of this magnitude is assured due to the CO2 already released into the atmosphere.
The disappearance of summer sea will have an immediate, and probably irreversible, impact upon polar bears, seals and other marine mammals. The loss of the highly reflective ice surface will also mean increased absorption of solar energy by the darker ocean surface and result in a warming of the water. The cold arctic waters are among the most biologically productive ecosystems in the world. At these waters warm productivity and fisheries will be negatively impacted. In addition, the warmer waters will effect ocean currents and increase the melting of the Greenland ice cap. The Greenland ice cap contains enough water to raise the level of the worlds oceans by approximately 7 meters (23 ft.), an event highly likely to occur within a couple of centuries, and an event that would have major consequences for Pacific islands and such major cities as New York City , Washington DC, Lagos, Bangkok, and Burns Aires. Thus a slight temperature increase will push the Arctic summer sea ice over the tipping point and will set off a global chain of reactions lasting centuries, and having multiple, major impacts upon mankind.
Alarmingly, another tipping point with about the same time-frame exists for the West Antarctic ice sheet, much of bottom of which is exposed to sea water, and which contains about as much fresh water, as ice, as the Greenland ice cap. Additional tipping points include: deforestation of the Amazon, loss of the northern evergreen forests, disruption of the Indian summer monsoon (which really is currently underway), drastic alteration of both Pacific and Atlantic ocean currents. Drastic changes are also expected within 10 years in the rainfall patterns on the African subcontinent, but the models vary greatly in whether the result will be increased rainfall, increased drought, or just greater oscillation between the two extremes – all with great consequences for a region currently undergoing significant agricultural stress.
