Editing Climate variability and change (section)

=== The Cenozoic ===
Throughout the [[Cenozoic]], multiple climate forcings led to warming and cooling of the atmosphere, which led to the early formation of the [[Antarctic ice sheet]], subsequent melting, and its later reglaciation. The temperature changes occurred somewhat suddenly, at carbon dioxide concentrations of about 600–760 ppm and temperatures approximately 4&nbsp;°C warmer than today. During the Pleistocene, cycles of glaciations and interglacials occurred on cycles of roughly 100,000&nbsp;years, but may stay longer within an interglacial when [[orbital eccentricity]] approaches zero, as during the current interglacial. Previous interglacials such as the [[Eemian interglacial|Eemian]] phase created temperatures higher than today, higher sea levels, and some partial melting of the [[West Antarctic ice sheet]].

Climatological temperatures substantially affect cloud cover and precipitation. At lower temperatures, air can hold less water vapour, which can lead to decreased precipitation.<ref>{{Cite journal|last1=Haerter|first1=Jan O.|last2=Moseley|first2=Christopher|last3=Berg|first3=Peter|date=2013|title=Strong increase in convective precipitation in response to higher temperatures|journal=Nature Geoscience|volume=6|issue=3|pages=181–85|doi=10.1038/ngeo1731|bibcode=2013NatGe...6..181B|issn=1752-0908}}</ref> During the [[Last Glacial Maximum]] of 18,000 years ago, thermal-driven [[evaporation]] from the oceans onto continental landmasses was low, causing large areas of extreme desert, including [[polar desert]]s (cold but with low rates of cloud cover and precipitation).<ref name="OakRidge-1997" /> In contrast, the world's climate was cloudier and wetter than today near the start of the warm [[Atlantic period|Atlantic Period]] of 8000 years ago.<ref name="OakRidge-1997" />

==== The Holocene ====
[[File:Holocene Temperature Variations.png|right|thumb|upright=1.35|Temperature change over the past 12 000 years, from various sources. The thick black curve is an average.]]
The [[Holocene]] is characterized by a long-term cooling starting after the [[Holocene climatic optimum|Holocene Optimum]], when temperatures were probably only just below current temperatures (second decade of the 21st century),<ref>{{Cite journal|last1=Kaufman|first1=Darrell|last2=McKay|first2=Nicholas|last3=Routson|first3=Cody|last4=Erb|first4=Michael|last5=Dätwyler|first5=Christoph|last6=Sommer|first6=Philipp S.|last7=Heiri|first7=Oliver|last8=Davis|first8=Basil|date=30 June 2020|title=Holocene global mean surface temperature, a multi-method reconstruction approach|journal=Scientific Data|language=en|volume=7|issue=1|page=201|doi=10.1038/s41597-020-0530-7|pmid=32606396|pmc=7327079|bibcode=2020NatSD...7..201K|issn=2052-4463|doi-access=free}}</ref> and a strong [[African Monsoon]] created grassland conditions in the [[Sahara]] during the [[Neolithic Subpluvial]]. Since that time, several [[stadial|cooling events]] have occurred, including:

*the [[Piora Oscillation]]
*the [[Middle Bronze Age Cold Epoch]]
*the [[Iron Age Cold Epoch]]
*the [[Little Ice Age]]
*the phase of cooling c. 1940–1970, which led to [[global cooling]] hypothesis

In contrast, several warm periods have also taken place, and they include but are not limited to:
*a warm period during the apex of the [[Minoan civilization]]
*the [[Roman Warm Period]]
*the [[Medieval Warm Period]]
*[[Modern Warming|Modern warming]] during the 20th century

Certain effects have occurred during these cycles. For example, during the Medieval Warm Period, the [[American Midwest]] was in drought, including the [[Sand Hills (Nebraska)|Sand Hills of Nebraska]] which were active [[sand dune]]s. The [[black death]] plague of ''[[Yersinia pestis]]'' also occurred during Medieval temperature fluctuations, and may be related to changing climates.

Solar activity may have contributed to part of the modern warming that peaked in the 1930s. However, solar cycles fail to account for warming observed since the 1980s to the present day.{{Citation needed|date=September 2016}} Events such as the opening of the [[Northwest Passage]] and recent record low ice minima of the modern [[Arctic shrinkage]] have not taken place for at least several centuries, as early explorers were all unable to make an Arctic crossing, even in summer. Shifts in [[biome]]s and habitat ranges are also unprecedented, occurring at rates that do not coincide with known climate oscillations {{Citation needed|date=September 2016}}.