Proxy reconstructions for the climate of the Quaternary Period are considerably more abundant and reliable than for earlier periods. The Quaternary spans the last 2Ma of Earth history and is separated into two Epochs, the Pleistocene (2Ma to 10Ka) and the Holocene (10Ka to present). In the preceding section, evidence that the Earth had entered a long-term climatic decline, was reviewed. For at least the last 10Ma, and probably much longer, the Earth has been in the grip of a long-term ice age. This ice age has continued during the Quaternary, and is in evidence today, as ice caps remain at both poles. Nevertheless, within the Quaternary, global climate has fluctuated between times of relative warmth and frigidity. This section will review the evidence for these fluctuations, and discuss their probable causal mechanisms.