Global Warming May Lead To A New Ice Age:
The basic chemistry behind global warming is very simple and not in dispute. Carbon dioxide (CO2) traps heat in the atmosphere. Through 1. burning fossil fuels, and 2. the clearing of forests over vast areas, humanity is adding carbon dioxide to the atmosphere faster than it can be absorbed by natural processes. Deforestation also reduces the biosphere’s capacity to process CO2 at the same time that it adds more. Consequently, it follows logically that the atmosphere should become warmer and the climate should heat up over time, melting ice caps, raising ocean water levels, and shifting climate zones northwards.
Strangely, however, there is one theory which suggests that global warming could actually lead to the onset of a new ice age! Interestingly, this theory did not arise directly from the whole global warming debate at all. Rather, it arose independently, from the field of paleoclimatology.
Paleoclimatology studies the history of climate change, such as the periodic shifts between ice ages and relatively warm periods. These shifts have happened throughout the Earth’s geological history. More specifically, the theory in question arises from attempts to understand what triggers the onset of an ice age.
As William Calvin (1998) points out, the Earth’s climate has periodically “flipped” back and forth between two states, with long periods of cold temperatures, or ice ages, being punctuated by shorter warm periods. Evidence also suggests that these changes from warmer to cooler periods (or the reverse) have often occurred relatively rapidly on a geological time scale. This is very much the opposite of the gradual changes which most global warming theorists predict for current warming trends.
Studies of paleoclimatology are partly based upon ice cores and other data taken from Greenland and Antarctica. Ice cores contain annual layers much like tree rings, which provide a record of changes in air temperature and the composition of the atmosphere for approximately the last 250,000 years. This period covers two major ice ages, the last of which ended about 11-12,000 years ago. Thus, global climate has tended to be “bi-modal” on a geological time scale, with relatively rapid flips between ice ages and warmer periods.
Paleoclimatologists are just beginning to propose hypotheses to explain how these rapid flips might work. One of the keys, as Calvin points out, may lie in changes in the movement of ocean currents. Ocean currents are much like great rivers in the sea, which carry water of different temperatures and different salinity levels from one area of the planet to another.
For example, at present the North Atlantic current carries warm surface waters all the way from the Pacific Ocean up to Iceland, which helps to warm the air in that area, as well as to keep the climate in northern Europe much warmer than the climate at similar latitudes in North America. London, England, for example, has a similar latitude to my home town of Winnipeg, Canada, but a much more temperate climate. This is because prevailing winds blowing eastward off the North Atlantic help to keep Europe’s temperature warmer.
The North Atlantic current then sinks as the water becomes salt laden and cools, and the return flow carries cooler, saltier water back the way it came into the Pacific Ocean. The Pacific, because it has more water to dilute it’s salt content, is not as salty as the Atlantic. Once again, then, ocean currents are part of a global salt-circulation and temperature circulation system within the planet’s oceans.
The theory is that climate flips may be linked to changes in “salt-flushing.” Salt-flushing refers to the sinking of cooler, heavier, salt-laden waters in the North Atlantic before the current begins its subsurface return journey. It is possible, the theory further suggests, that salt-flushing could fail for several reasons. And if salt-flushing failed frequently enough, it could cause those warm surface waters to stop traveling so far north, thus changing the climate of Europe.
Calvin provides two main reasons why salt-flushing, or the sinking of salt-laden waters, could be caused to fail in the North Atlantic and be pushed further south, both of which are likely to be promoted by global warming, and both of which are related to one another.
1. The first is an increase in the amount of floating ice. As Greenland’s ice sheet melts, the amount of ice chunks, or ice bergs falling into the ocean also increases. More floating ice reduces the amount of the ocean’s surface exposed to winds, which in turn reduces evaporation. Yet evaporation is needed to make the water heavy enough and salty enough to sink.
2. The melting of Greenland’s ice sheets, and more floating ice also means the addition of large amounts of fresh water to the North Atlantic, which also dilutes the salt heavy surface waters before they become unstable enough to begin sinking.
Together, these factors could affect how far north warm surface currents currently travel.
What Calvin suggests is that a run of failures in salt-flushing, and the resulting shifts in ocean currents, may be the trigger which flips global climate from warm periods into ice ages. So paradoxically, if this theory is correct, global warming could in fact be the trigger for another ice age, especially by melting Greenland’s ice sheet, diluting the North Atlantic, and preventing salt-flushing. This could rapidly cool Europe’s climate, lead to a re-expansion of ice in northern Europe and snowball from there. Increasing surface and sea ice, for example, reflects more of the sun’s heat back into space, thus further contributing to cooling. And if events proceeded as quickly as they are known to have in past climate flips, this could take place relatively rapidly, even on a human time scale.
This whole theory is also one of the best examples in the scientific literature of the fact that complex systems, such as global climate, ecosystems and the biosphere, do not behave like mechanical systems. What Calvin is suggesting is that turning up the heat could lead to a rapid cooling as the larger system over compensates-the larger system including all of the complex interactions between atmospheric temperature, ocean temperature, salt content in the ocean, and the movement of ocean currents, among other factors.
This type of “abrupt” shift in a previously stable state, or trend in complex systems is known as a “discontinuity” in the ecological literature (Bright 2000). It is also a very good example of the unpredictability of complex organic systems generally.
References, additional readings:
Chris Bright (2000) “Environmental Surprises: Planning for the Unexpected,” The Futurist, July/August.
William H. Calvin (1998) “The Great Climate Flip-Flop,” The Atlantic Monthly, January.
