For the past millions of years, the earth has been fluctuating between two different states of dominant climate: Greenhouse and Icehouse. These two climate sets are complete opposites from each other and is on a continuing, uneven cycle between the two. In fact, they are completed opposites especially when looking at a main culprit of these changes in paleoclimate: carbon dioxide.

Greenhouse Earth, which is often called a “Hothouse Earth” in many sources, signifies that there are no continental glaciers whatsoever on the planet and usually note for their high levels of Carbon Dioxide(CO2) and other greenhouse gas such as water vapor and methane, and its high temperatures that, on the sea-surface temperatures (SSTs), could range from 28 ° C (82.4 °F) in the tropical areas (the area between the Tropics of Cancer and Capricorn) and at 0° C (32° F) in the polar regions.

Icehouse Earth contains as what it name states: ice. On an icehouse Earth, continental ice sheets exist and wax and wane throughout time known as glacial (ice age) and interglacial periods. During icehouse Earth, greenhouse gases tend to be less abundant and temperatures tend to be cooler globally. In fact, we are currently living in an icehouse age; we have ice sheets on both poles, and we have had recent periods of ice age in the past few centuries .

What people believe to be global warming and climate change are close to the truth. As we live in an icehouse Earth time period, we are heading back towards a greenhouse Earth. Ice is actually a rare phenomenon on Earth, occurring during the 20% of the time that the planet is under an icehouse effect . Understanding what causes the icehouse effect and how it can change to a greenhouse state, and then back, is important to even modern day scientists, since human life has not existed within a greenhouse environment, as many species such as the crocodile and other modern “prehistoric” reptiles have witnessed. The argument between the “conflicting” ideas of global warming and climate change within the past decade may actually be the same thing, but consisting of another, natural event that humans tend to be naïve about.

How is Research Done over these Effects?

There are many ways that scientists can discover what the climate was like over these millions of years. The most common way is through the use of proxies, which are preserved physical characteristics of the world from the past. Through the use of isotopes (atoms through a chemical element that differ from each other in ways of the number of neutrons each atom holds), scientists can be used to create hindsight models, which in turn can show others what the world was like. Common proxies involve ice cores, tree rings, ocean and lake sediments, and even fossilized pollen. Used more commonly, however, are ocean and lake sediments. From such proxies, scientists have determined that the atmospheric carbon dioxide of the earth could have been up at least 350 times higher than our modern day levels. One study has shown that atmospheric carbon dioxide levels during the Permian age rocked back and forth between 250 parts per million, which is close to our modern day levels, up to 2,000 parts per million . Also shown from models taken from lake sediments, the “Hothouse” or “super Greenhouse” Eocene was in a state of a “permanent El Nino state” after the 10° C warming of the deep ocean and high latitude surface temperatures shut down the Pacific Ocean’s El Nino-Southern Oscillation . A theory was conducted for the Paleocene-Eocene Thermal Maximum on the sudden decrease of carbon isotopic composition of global inorganic carbon pool by 2.5 parts per million . A hypothesis noted for this negative drop of isotopes could be the increase of methane hydrate, which the trigger remains a mystery. This increase of methane in the atmosphere, which happens to be a potent, but short-lived greenhouse gas, increased the global temperatures by 6°C with the assistance of the less potent carbon dioxide.

What causes the Greenhouse Effect?

The causes for the Greenhouse Effect on the world are hard to pinpoint, but there are quite a few ideas for what causes the rise of this world state. Since CO2 and other greenhouse gases are abundant during this time, especially when tectonic movement are extremely active during the more well known Greenhouse ages, such as 368 million years ago in the Paleozoic Era. Because of continental rifting, or continental plates moving away from each other, volcanic activities become more prominent, producing more CO2 and heating up the Earth and atmosphere . Earth is more commonly placed in a Greenhouse state throughout the epochs, and this state takes up approximately 80% of the time that Earth has been around, which makes it a little more difficult to narrow down on direct causes .

What causes the Icehouse Effect?

The icehouse state of Earth is a little more complex than the greenhouse state. This is because not much is really known about the transition periods between greenhouse to icehouse climates and what could make the climate so different. One thing that has been discussed has been the decline of CO2 in the atmosphere, which means that this could be a dead time for volcanic activity.

One other thought happens to deal with tectonic plates and the opening and closing of oceanic gateways . A reason that this would play a part in Icehouse Earth is that it could bring forth cool waters from even deep water circulations that could assist and creating ice sheets or thermal isolation of areas. An example of this happening is the opening of the Tasmanian gateway 36.5 million years ago that separated Australia and Antarctica that set off the Cenozoic icehouse (Exon, Kennet and Malone) , and then the creation of the Drake Passage 32.8 million years ago by the separation of South America and Antarctica , though it was believed by other scientists that this did not come into effect until around 23 million years ago . The closing of the Isthmus of Panama and the Indonesian seaway approximately 3 or 4 million years ago may have sealed the deal for our current Icehouse state .
For the icehouse climate, tectonic activity also creates mountains, which are produced by one continental plate colliding with another one and continuing forward. The revealed, “fresh” soils act as a scrubber of CO2, which in turn declines the amount of Carbon Dioxide in the atmosphere. A good example happens to be the collision between the Indian subcontinent and the Asian continent, which created the Himalayan Mountains about 50 million years ago.

Glacial and Interglacial

Within Icehouse states, there are glacial and interglacial periods that causes ice sheets to build up or retreat. The causes for these periods of glacial and interglacial connect to the movement of the earth around the earth . The astronomical components, discovered by the Yugoslavic astronomer Milutin Milankovitch, include the tilt of the earth, the eccentricity, or shape of the orbit, and the precession, or wobble, of the earth’s spin. The tilt of the axis tends to fluctuate between 21.5 ° to 24.5 ° and back every 41,000 years on the vertical axis. This change actually affects the seasonality upon the earth by way that more solar radiation would hit certain areas of the planet more often on a higher tilt, while less of a tilt would create a more event set of seasons worldwide. These changes can be seen in ice cores, which contains also the information that shows that, during glacial times, or a maximum reach of ice sheets, have lower rates of atmospheric carbon dioxide. This may be caused from the increase or redistribution of the acid/ base balance with “bicarbonate and carbonate ions” that deals with alkalinity. What remains interesting about glacial and interglacials periods is that only 20% of the time during an Icehouse state is spent in interglacial, or warmer, times .

The Snowball Effect

The Snowball Effect is the complete opposite of the Greenhouse effect when it comes to climate, but technically, they do not have continental ice sheets like the Earth does during the Icehouse state. “The Great Infra-Cambrian Ice Age” has been claimed to be the host of such a world, and in 1964, the scientist W. Brian Harland brought forth his discovery of indications of glaciers in low latitudes (Harland and Rudwick). This became a problem for Harland because of the thought of the “Runaway Snowball Paradox” that, once the earth enters the route of becoming a Snowball Earth, it would never be able to leave that state. For a long time, this had been silenced, until 1992 when Joe Kirschvink brought up a solution for the “Runaway Snowball Paradox.” It is believed that since the continents at this time were huddled at the low and mid-latitudes that there was a great cooling event by planetary albedo, or reflection of the earth’s surface. Kirschvick explained that the way to get out of the snowball could be connected to carbon dioxide, since volcanic activity would not halt, and that the build up and lack of “scrubbing” of this carbon dioxide in the atmosphere, that the earth would return to a greenhouse state. In fact, after this snowball occurred, there was an event called the Cambrian Explosion, which produced plenty of multi-celled organisms soon after Snowball Earth came to a close . Arguments resumed, this time from biologists who claim that photosynthetic life would not survive without sunlight underneath many meters of ice. However, it has been noticed that, even under meters of thick ice around Antarctica, sunlight shows through, which disproves that idea. With Snowball Earth, it has been decided that a “hard” Snowball Earth, one completely covered by snow, is basically impossible. But, the idea of a “slush ball” earth, with points of openings near the equator, could actually be possible.

Recent studies may have complicated this state of Earth’s climate again. In October, 2011, a team of French researchers have announced that the carbon dioxide during this known “Snowball Earth” may have been lower than originally stated, which provides a challenge in finding out how Earth was able to get out of its state, if it was even a snowball, or even a slush ball, in its climate state .

What causes a Transition between Greenhouse and Icehouse Earth, and vice versa?

From these transitions from greenhouse to icehouse, and vice versa, there has been much mass extinction across the planet. In fact, “ 99.99% of all life that has ever existed is extinct” , with the dinosaurs being the most popular, though that may actually have something to do with a meteorite hitting earth and helping cause a large amount of volcanic eruptions.

A study was done over the Eocene, which occurred between 53 and 49 million years ago. This also happened to be the Earth’s warmest temperature sets in 100 million years . However, this “super-greenhouse” soon became an icehouse by the late Eocene. It was believed that the decline of CO2 caused this change back then, though there are possible positive feedbacks, or added influence that contributes to the cooling.

Our only record the modern world has for a transition from an icehouse planet to a greenhouse planet where plant life exists happens to be during the Permian Epoch that occurred around 300 million years ago. In 40 million years, this transition took place, causing the Earth to change from a moist, icy planet where rainforests covered the tropics, and into a hot, dry, and windy location where little could survive. Isabel Montanez, a professor who has researched into this time period found the climate to being “highly unstable” and “marked by dips and rises in carbon dioxide”.

The Modern Day

Currently, we are in an icehouse climate state. About 34 million years ago, we started our icehouse state, as ice sheets began to form in Antarctic; the ice sheets in the Arctic didn’t start forming until 2 million years ago. Some processes that may have led to our current icehouse may be connected to the development of the Himalayan Mountains and the opening of the Drake Passage between South America and Antarctica. Scientists have been attempting to compare the past transitions between icehouse and greenhouse, and vice versa to understand where our Earth is heading. There are a few problems with this though. First off, we are heading into a greenhouse faster than any other time in the past. This is due to the burning of fossil fuels, the victims of the past icehouse and greenhouse transitions. Tectonic plates have become more active in more recent days than they have in a long time.