By John L. Casti

One of the charms of living in the center of Vienna is the opportunity to regularly visit the Kunsthistorisches Museum, a place that’s on everyone’s list of the world’s 10 great art museums. One of the museum’s highlights is Pieter Brueghel the Elder’s 1565 painting “Hunters in the Snow.”

This haunting work shows three hunters returning from a hunting expedition accompanied by their dogs. By appearances, the expedition was not successful: the hunters seem to trudge wearily through the deep winter snow, and the dogs look pretty miserable themselves.

The weather depicted in the painting appears to be a calm, cold, overcast day; the trees are bare of leaves; wood smoke hangs in the air and in the background we see ice skaters skimming over a frozen lake.

Little Ice Age

In fact, according to many climatologists, these two paintings fairly accurately bound a period now called the Little Ice Age (LIA), which seems to have begun around 1550 and lasted for about three centuries.

During this time winters in Europe and North America were considerably colder than previously, with the river Thames in England and canals in Holland often freezing over. Even in Turkey this climatic change showed itself as the southern section of the Bosphorus froze over in 1622.

Not to be outdone by Europe, it’s reported that Lake Superior in North America had ice until June in 1607, and in the winter of 1780 New York harbor froze solid enough that people could walk from Manhattan to Staten Island.

Perhaps the best account of the entire LIA is the book of the same name by Brian Fagan of the University of California. Fagan says that the peasants of the time suffered not only bone-chilling weather, but also famines, bread riots, and the appearance of brutal leaders.

Fagan writes that by the late 17th century, agricultural production had dropped so precipitously that “alpine villagers lived on bread made from ground nutshells mixed with barley and oat flour.” Fagan goes on to note that life was especially difficult for those in the French Alps. Advancing glaciers moved forward “over a musket shot each day, even in the month of August.” And when the glaciers finally retreated, they left land so barren that no crops would grow.

Interestingly, the evidence of this global cooling period is somewhat less detailed for other parts of the world, especially the southern hemisphere. But this is not to say a LIA was any less severe below the equator, but only that documented evidence in the form of paintings, writings and the like is simply much scantier. However, ocean sediment cores from Antarctica to Africa seem to point to the same phenomenon.

Prolonged period of cooling

Leaving aside causes internal to the global climatic system itself, such as oceanic currents, interactions between the atmosphere and the seas, surface reflection (albedo) and the like, climatologists have narrowed the search for the proximate cause of the LIA to two factors: sunspots and volcanic activity.

In the first, solar radiation takes a nosedive and so radiation striking the Earth was severely reduced, while in the second case volcanoes spew forth massive clouds of dust and volcanic ash leading to the same type of reduction in solar radiation striking the Earth’s surface. Finally, there is the endogenous cause involving a shutdown of the famed “Great Ocean Conveyor,” which moves warm water from the equatorial regions across the north Atlantic as the Gulf Stream current that warms northern Europe. If this dynamic is shut down by, say, an injection of large amounts of fresh water to the north Atlantic by means perhaps of a period of warming, then something akin to the LIA can be expected. We’ll return to this point a bit later, as it is a process that climatologists worry about today.

The example of the LIA shows that there are several possibilities for setting off an ice age. Volcanoes and sunspots are but two of a long list of possible culprits. So before proceeding, let’s take a page or two to detail the “top 10” possible causes of a new ice age.

10 ways to start an ice age

The 2004 film “The Day After Tomorrow” is based on disruption of the ocean conveyor that brings warm water to the Northern Hemisphere. The plot of the film revolves about melting polar ice that leads to a lot of fresh water from the northern polar region disrupting the flow of warmer water.

In the movie, three massive storms gather across the Earth and then combine into a planet-wide storm. The eye of this “perfect storm” is able to suck very cold air from the upper atmosphere to the ground, causing a flash freeze anywhere it touches.

The United States becomes a vast tundra reminiscent of Siberia at its worst, and even the southern half of the U.S. tries to relocate to Mexico. The Mexicans then briefly close the border, but it’s re-opened when the U.S. President agrees to forgive all Latin American debt.

We should immediately note that there is not a shred of climatological science in the events portrayed in the film. All this having been said, the take-home message of this fanciful expression of some of the possible consequences of global warming is that the climate can do stranger things than are dreamt of in our philosophies.

So we should be alert to even highly unlikely scenarios for rapid climate change. In particular, ice ages can come quickly or slowly from many sources.

There are basically three different sources for an ice age: actions taking place in outer space, geophysical events on earth, and harmful human activity. Let’s quickly review 10 different scenarios within these three broad categories:

The first three entries on our Top 10 list involve various changes in either the Earth’s orbit around the Sun or in the Earth’s planetary alignment, all of which reduce the solar radiation falling on the planet’s surface.

?Widening of the earth’s orbit around the sun: Presently, the earth moves about the sun in an orbit that is very nearly a circle. This means that the amount of solar radiation falling on the earth is pretty much constant throughout the year, although of course some regions get more radiation than others due to the tilt of the earth’s axis of rotation. But the earth’s orbit widens very slowly, and in about 50,000 years it will be much more elliptical rather than circular. At that time there will be less solar radiation, on average, than there is today. Specialists believe that this is the primary cause of ice ages.

?Change of the tilt of the earth’s axis of rotation: The axis of the Earth’s rotation is not straight up-and-down but is tilted a bit with respect to the plane of its movement around the Sun. As the Earth moves around the Sun, this tilt is what causes the change of seasons. But the axis slowly tips and then moves back more toward the vertical. When the axis is straight up-and-down, we have warmer winters and cooler summers. In these periods there will be more snow at the poles and in the summer less ice will melt. Presto! An ice age in the making. Fortunately, the axis of rotation won’t be vertical again for another 20,000 years or so.

?Wobble of the earth’s Axis of Rotation: When a spinning top loses energy, its axis of rotation starts to wobble before it finally falls over. The Earth’s axis of rotation also wobbles in just the same way as the top, one wobbly rotation taking about 23,000 years. Some researchers believe that this wobbling gives rise to temperature changes on the surface of the Earth that can also lead to an ice age.

?Meteor dust: Out beyond Neptune there is a large region consisting of many small bodies left over from the formation of the solar system. These bodies consist mostly of frozen methane, ammonia and water, and form what’s called the Kuiper Belt. Some astrophysicists believe a big asteroid from this region could explode, giving rise to a cloud of dust that would surround the Sun. The resulting reduction of solar radiation could then trigger an ice age on Earth.

?Space clouds: Out in deep space there are vast clouds of dust and gas. Occasionally, our solar system passes through one of these clouds in a passage that takes millions of years. This passage blocks out solar radiation causing “super” ice ages that occurred hundreds of millions of years ago. Or so theorists say.

Earth

?Volcanoes: Volcanic eruptions of the “super” type that occurred in Yellowstone National Park more than 600,000 years ago can also cause an ice age.

Such an eruption blow so much soot, gas and dust into the atmosphere that sunlight is blocked out for years. The cooling Earth then experiences “eternal” winter and, hence, a very long ice age.

?Collapse of the Gulf Stream: We’ve already outlined how the Gulf Stream current across the North Atlantic can sometimes shut down, an effect that most likely caused the Little Ice Age discussed earlier.

?Thinning of the atmosphere: There are several processes, including a human induced reduction of greenhouse gases, that can remove carbon dioxide and methane from the atmosphere.

Interestingly, without these gases the Earth would cool dramatically from the loss of its “heat blanket,” and almost surely touch off an ice age.

?Tectonic shifts: The Earth’s continents slowly move around into different configurations on a geological timescale. At times, they form one huge super continent. At other times, the land masses break up into many smaller continents like we see today. A continent like Antarctica at a pole is especially dangerous, since if it breaks up huge amounts of ice are deposited into the seas triggering off conditions for a new ice age.

Human activity

?¬Nuclear war: In another chapter we’ve recounted the phenomenon of “nuclear winter,” in which use of ground-burst nuclear weapons in a war sends vast amounts of dust, soot and other contaminants into the atmosphere, much like the situation described above for a big volcanic eruption. The end result is the same: a large reduction in sunlight striking the surface of the Earth for many months, if not years, leading to cooling and some type of ice age.

This list is by no means exhaustive. But it provides much ammunition supporting the contention that the dawning of a new ice age is definitely not science fiction. It’s happened before and it will definitely happen again.

Adding it all up

It’s important to again emphasize that transitions between radically different climatic regimes can take place over very short time periods, often just a decade or two.

These transitions are what system theorists would term an “extreme event,” and there is an emerging theory of such events suggesting they occur in “bursts.” Thus, a transition from one qualitatively different state to another in a time period very short relative to the overall time frame of the phenomenon, here global climatic change, followed by a very long period in the new state.

Hot or cold

On one side we have the global warmers. The upward thrust of the Earth’s temperature, along with consequent phenomena like melting of polar ice, is incontrovertible — whether or not it’s caused and/or exacerbated by human activity.

Following the by-now-standard scenario, this temperature change will continue for many decades and ultimately shift populations and lifestyles to entirely new regimes. It’s not necessary to detail these matters here, as the scientific and popular press have decimated several forests already with their account of these dire straits.

On the other side of the ledger are what we might term the “global coolers,” who argue for a trip to the deep freeze rather than the oven is at least as likely a scenario. Our story in this article has given the main reasons underlying this rather unfashionable, and certainly much-less chronicled, view.

While the majority of climatologists pooh-pooh the likelihood of the freezer as opposed to the oven, it is a scenario that is not at all implausible or in any way unscientific.

It has happened before and will surely happen again. The only question is how and when. Our assessment is that it’s more than a long shot, thus probably not the way to bet, at least if your timescale is a few decades.

Environment info
Ocean level

The possible causes and specific contributions to fast sea level rise and the uncertainties are very large, particularly for Antarctica.

However, in general it appears that the observed rise can be explained by thermal expansion of the oceans, and by the increased melting of mountain glaciers and the margin of the Greenland ice sheet. From present data it is impossible to judge whether the Antarctic ice sheet as a whole is currently out of balance and is contributing, either positively or negatively, to changes in sea level.

Future changes in sea level were estimated for each of the Intergovernmental Panel on Climate Change (IPCC) forcing scenarios in future predictions.

For each scenario, three projections – best estimate, high and low – were made corresponding to the estimated range of uncertainty in each of the potential contributing factors.

It is found that: For the IPCC Business-as-Usual Scenario at year 2030, global-mean sea level is 8-29cm higher than today, with a best-estimate of 18cm. At the year 2070, the rise is 21-71cm, with a best-estimate of 44cm.

Most of the contribution is estimated to derive from thermal expansion of the oceans and the increased melting of mountain glaciers and small ice caps.

Source: Universitreit Utrecht

John L. Casti (casti@iiasa.ac.at) is a senior research scholar at the International Institute for Applied Systems Analysis in Laxenburg bei Wien, Austria. He is also the founder of the X-Center, a Vienna-based society for exploration of the extreme events and uncdertainty. His most recent book is Mood Matters: From Rising Skirt Lengths to the Collapse of World Powers (Copernicus Books, New York, 2010). His new book, XEVENTS, will be published by HarperCollins, NY, in early 2012 and in Korean by the end of 2012.