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The terms greenhouse and icehouse Earth refer to the prevailing global climate on a timescale of millions of years.

During a greenhouse Earth period, the planet's atmosphere contains sufficient greenhouse gases such as carbon dioxide and methane for ice to be entirely absent from the planet's surface.^{verification needed}

During icehouse periods, glaciers are present in fluctuating amounts; variations in the Earth's orbit may result in many ice ages, glacials, and interglacials.

The current icehouse period had its beginnings ~50 million years ago; a blooming of freshwater plants in the Arctic Ocean may have contributed to its initiation.