Greenhouse and icehouse Earth

[3] Greenhouse and icehouse periods have played key roles in the evolution of life on Earth by directly and indirectly forcing biotic adaptation and turnover at various spatial scales across time.

[6] Additionally, the levels of carbon dioxide and other greenhouse gases (such as water vapor and methane) are high, and sea surface temperatures (SSTs) range from 28 °C (82.4 °F) in the tropics to 0 °C (32 °F) in the polar regions.

[15] The fluctuation of the ice sheets results in changes in regional climatic conditions that affect the range and the distribution of many terrestrial and oceanic species.

There have been three periods of glaciation in the Phanerozoic Eon (Ordovician, Carboniferous, and Cenozoic), each lasting tens of millions of years and bringing ice down to sea level at mid-latitudes.

Transitions from Phanerozoic icehouse to greenhouse intervals coincided with biotic crises or catastrophic extinction events, indicating complicated biosphere-hydrosphere feedbacks.

[39] The glacial and interglacial periods tend to alternate in accordance with solar and climatic oscillation until Earth eventually returns to a greenhouse state.

[17] Earth will likely phase into another interglacial period such as the Eemian, which occurred between 130,000 and 115,000 years ago, during which evidence of forest in North Cape, Norway, and hippopotamus in the Rhine and Thames Rivers can be observed.

[16] Earth is expected to continue to transition between glacial and interglacial periods until the cessation of the Quaternary Ice Age and will then enter another greenhouse state.

[18][10][11] Potential drivers of previous icehouse states include the movement of the tectonic plates and the opening and the closing of oceanic gateways.

[19] They seem to play a crucial part in driving Earth into an icehouse state, as tectonic shifts result in the transportation of cool, deep water, which circulates to the ocean surface and assists in ice sheet development at the poles.

[7] Examples of oceanic current shifts as a result of tectonic plate dynamics include the opening of the Tasmanian Gateway 36.5 million years ago, which separated Australia and Antarctica,[20][21] and the opening of the Drake Passage 32.8 million years ago by the separation of South America and Antarctica,[21] both of which are believed to have allowed for the development of the Antarctic ice sheet.

The closing of the Isthmus of Panama and of the Indonesian seaway approximately 3 to 4 million years ago may also be a contributor to Earth's current icehouse state.

[23] One proposed driver of the Quaternary Ice age is the collision of the Indian Subcontinent with Eurasia to form the Himalayas and the Tibetan Plateau.

[17] Under that paradigm, the resulting continental uplift revealed massive quantities of unweathered silicate rock CaSiO3, which reacted with CO2 to produce CaCO3 (lime) and SiO2 (silica).

[24] Model simulations suggest that the current interglacial climate state will continue for at least another 100,000 years because of CO2 emissions, including the complete deglaciation of the Northern Hemisphere.

A major transition took place over the subsequent 40 million years and caused Earth to change from a moist, icy planet in which rainforests covered the tropics to a hot, dry, and windy location in which little could survive.

Professor Isabel P. Montañez of University of California, Davis, who has researched the time period, found the climate to be "highly unstable" and to be "marked by dips and rises in carbon dioxide.

[33] Some processes that may have led to the current icehouse may be connected to the development of the Himalayan Mountains and the opening of the Drake Passage between South America and Antarctica, but climate model simulations suggest that the early opening of the Drake Passage played only a limited role, and the later constriction of the Tethys and Central American Seaways is more important in explaining the observed Cenozoic cooling.

[34] Scientists have tried to compare the past transitions between icehouse and greenhouse, and vice versa, to understand what type of climate state Earth will have next.

Hypothetical runaway greenhouse state Tropical temperatures may reach poles Global climate during an ice age Earth's surface entirely or nearly frozen over