Explanation:

These two climate states last for millions of years and should not be confused with glacial and interglacial periods, which occur only during an icehouse period and tend to last less than 1 million years.
There are five known great glaciations in Earth's climate history; the main factors involved in changes of the paleoclimate are believed to be the concentration of atmospheric carbon dioxide, changes in the Earth's orbit, and oceanic and orogenic changes due to tectonic plate dynamics. Greenhouse and icehouse periods have profoundly shaped the evolution of life on Earth.
A "greenhouse Earth" or "hothouse Earth" is a period in which there are no continental glaciers whatsoever on the planet, 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.
An "icehouse Earth" is the earth as it experiences an ice age. Unlike a greenhouse Earth, an icehouse Earth has ice sheets present, and these sheets wax and wane throughout times known as glacial periods and interglacial periods.
During an icehouse Earth, greenhouse gases tend to be less abundant, and temperatures tend to be cooler globally. The Earth is currently in an icehouse stage,[5] as ice sheets are present on both poles and glacial periods have occurred at regular intervals over the past million years