<div class="thumb tright"><div class="thumbinner" style="width:252px;"><a href="//commons.wikimedia.org/wiki/File:Five_Myr_Climate_Change.png" class="image"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Five_Myr_Climate_Change.png/250px-Five_Myr_Climate_Change.png" decoding="async" width="250" height="75" class="thumbimage" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Five_Myr_Climate_Change.png/375px-Five_Myr_Climate_Change.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Five_Myr_Climate_Change.png/500px-Five_Myr_Climate_Change.png 2x" data-file-width="745" data-file-height="224"></a>  <div class="thumbcaption"><div class="magnify"><a href="//commons.wikimedia.org/wiki/File:Five_Myr_Climate_Change.png" class="internal" title="Enlarge"></a></div>Expanded view of climate change during the last five million years, showing the rapid oscillations in the glacial state.</div></div></div>
<div class="thumb tright"><div class="thumbinner" style="width:252px;"><a href="//commons.wikimedia.org/wiki/File:Phanerozoic_Climate_Change.png" class="image"><img src="https://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Phanerozoic_Climate_Change.png/250px-Phanerozoic_Climate_Change.png" decoding="async" width="250" height="179" class="thumbimage" srcset="https://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Phanerozoic_Climate_Change.png/375px-Phanerozoic_Climate_Change.png 1.5x, https://upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Phanerozoic_Climate_Change.png/500px-Phanerozoic_Climate_Change.png 2x" data-file-width="726" data-file-height="520"></a>  <div class="thumbcaption"><div class="magnify"><a href="//commons.wikimedia.org/wiki/File:Phanerozoic_Climate_Change.png" class="internal" title="Enlarge"></a></div>View of climate change extending back through the last 540 million years, including many cycles of change from warm to cold and back again.</div></div></div>
<p>This figure shows <a href="https://en.wikipedia.org/wiki/climate_change" class="extiw" title="w:climate change">climate change</a> over the last 65 million years.  The data are based on a compilation of <a href="https://en.wikipedia.org/wiki/oxygen" class="extiw" title="w:oxygen">oxygen</a> <a href="https://en.wikipedia.org/wiki/isotope" class="extiw" title="w:isotope">isotope</a> measurements (δ<sup>18</sup>O) on <a href="https://en.wikipedia.org/wiki/benthic" class="extiw" title="w:benthic">benthic</a> <a href="https://en.wikipedia.org/wiki/foraminifera" class="extiw" title="w:foraminifera">foraminifera</a> by Zachos et al. (2001) which reflect a combination of local <a href="https://en.wikipedia.org/wiki/temperature" class="extiw" title="w:temperature">temperature</a> changes in their environment and changes in the isotopic composition of <a href="https://en.wikipedia.org/wiki/Seawater" class="extiw" title="en:Seawater">sea water</a> associated with the growth and retreat of continental <a href="https://en.wikipedia.org/wiki/ice_sheet" class="extiw" title="w:ice sheet">ice sheets</a>.
</p><p>Because it is related to both factors, it is not possible to uniquely tie these measurements to temperature without additional constraints.  For the most recent data, an approximate relationship to temperature can be made by observing that the oxygen isotope measurements of Lisiecki and Raymo (2005) are tightly correlated to temperature changes at <a href="https://en.wikipedia.org/wiki/Vostok,_Antarctica" class="extiw" title="w:Vostok, Antarctica">Vostok</a> as established by Petit et al. (1999).  Present day is indicated as 0.  For the oldest part of the record, when temperatures were much warmer than today, it is possible to estimate temperature changes in the polar oceans (where these measurements were made) based on the observation that no significant ice sheets existed and hence all fluctuation in (δ<sup>18</sup>O) must result from local temperature changes (as reported by Zachos et al.).
</p><p>The intermediate portion of the record is dominated by large fluctuations in the mass of the <a href="https://en.wikipedia.org/wiki/Antarctica" class="extiw" title="w:Antarctica">Antarctic</a> ice sheet, which first nucleates approximately 34 million years ago, then partially dissipates around 25 million years ago, before re-expanding towards its present state 13 million years ago.  These fluctuations make it impossible to constrain temperature changes without additional controls.
</p><p>Significant growth of ice sheets did not begin in <a href="https://en.wikipedia.org/wiki/Greenland" class="extiw" title="w:Greenland">Greenland</a> and <a href="https://en.wikipedia.org/wiki/North_America" class="extiw" title="w:North America">North America</a> until approximately 3 million years ago, following the formation of the <a href="https://en.wikipedia.org/wiki/Isthmus_of_Panama" class="extiw" title="w:Isthmus of Panama">Isthmus of Panama</a> by <a href="https://en.wikipedia.org/wiki/continental_drift" class="extiw" title="w:continental drift">continental drift</a>.  This ushered in an era of rapidly cycling <a href="https://en.wikipedia.org/wiki/ice_age" class="extiw" title="w:ice age">glacials and interglacials</a> (see figure at upper right).
</p>
Also appearing on this graph are the <a href="https://en.wikipedia.org/wiki/Eocene_Climatic_Optimum" class="extiw" title="w:Eocene Climatic Optimum">Eocene Climatic Optimum</a>, an extended  period of very warm temperatures, and the <a href="https://en.wikipedia.org/wiki/Paleocene-Eocene_Thermal_Maximum" class="extiw" title="w:Paleocene-Eocene Thermal Maximum">Paleocene-Eocene Thermal Maximum</a> (labeled PETM).  The PETM is very short lived high temperature excursion possibly associated with the destablization of <a href="https://en.wikipedia.org/wiki/methane_clathrate" class="extiw" title="w:methane clathrate">methane clathrates</a> and the rapid buildup of <a href="https://en.wikipedia.org/wiki/greenhouse_gas" class="extiw" title="w:greenhouse gas">greenhouse gases</a> in the atmosphere.  Due to the coarse sampling and averaging involved in this record, it is likely that the full magnitude of the PETM is underestimated by a factor of 2-4 times its apparent height.
<a href="//commons.wikimedia.org/wiki/User:Dragons_flight" title="User:Dragons flight">Robert A. Rohde</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>