Icehouse earth is the condition when the planet has continental glaciers. It is the cooler mode of earth’s climate, having occurred only approximately 15% of the time. We are currently in an icehouse mode, with long-term ice sheets in both the northern and southern hemispheres. Fluctuations between major glaciations and interstades are part of the icehouse condition. This current icehouse phase is known as the Quaternary and began roughly 2.58 million years ago.
The last glaciation, known in the US as the Wisconsinan, began about 100,000 years ago and ended roughly 12,000 years ago. We are currently in the warmer phase before, presumably, the next ice age would begin within the next 10,000 years. A few hypotheses explaining current icehouse conditions are the closing of the isthmus of Panama 3 million years ago, cutting the Pacific off from the Caribbean and Atlantic, and the collision of India with Asia, creating the Himalaya which are still growing. (The Indian plate made contact with Asia around 33 million years ago, around when the Antarctic ice sheet expanded to cover the whole continent.)
Carbon dioxide levels in the atmosphere are lower during icehouse conditions. Tectonic activity and the spatial arrangement of continents has a dominant impact on CO2 concentration in the atmosphere. The weathering of bedrock consumes carbon dioxide, so when weathering of rock occurs at higher rates, CO2 is removed from the atmosphere more quickly than the ocean and volcanic activity replaces it, lowering the concentration and depressing global temperature.
The fluid dynamics of the ocean are another major influence on global climate. By volume, water has more than 3000 times the heat capacity of air. The splitting of continents, such as when Australia and then South America were disconnected from Antarctica, left the southern continent isolated by cold water and led to further cooling there.
Tomorrow: plate tectonics.
This post was previously published on dailykos.com and is republished on Medium.
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