Paleoclimatology is the study of climate change taken on the scale of the entire history of Earth. It uses records from ice sheets, tree rings, sediment, and rocks to determine the past state of the climate system on Earth.
Techniques of paleoclimatology
Main articles: Geologic time scale and History of Earth Planet's timeline
Periodic Ice ages
Snowball Earth/Varangian glaciation (Hadean and Paleoproterozoic)
Permian-Triassic extinction event (Permian-Triassic)
Paleocene-Eocene Thermal Maximum (Paleocene-Eocene)
Younger Dryas/The Big Freeze (~11 000 BCE)
Holocene climatic optimum (~7000 BCE-3000 BCE)
Climate changes of 535-536 (535-536)
Medieval warm period (900-1300)
Little ice age (1300-1800)
Year Without a Summer (1816) Various notable climate-related events
History of the atmosphere
The earliest atmosphere of the Earth was probably stripped away by solar winds early in the history of the planet. These gases were later replaced by an atmosphere derived from outgassing from the Earth. Sometime during the late Archean Era an oxygen atmosphere began to develop from photosynthesizing algae.
Earliest atmosphere
Free oxygen did not exist until about 1,700 Ma and this can be seen with the development of the red beds and the end of the banded iron formations. This signifies a shift from a reducing atmosphere to an oxidising atmosphere. The early atmosphere and hydrosphere (up until about 2,000 Ma) were devoid of free oxygen. After photosynthesis developed, photoautotrophs began releasing O2.
The very early atmosphere of the earth contained mostly carbon dioxide (CO2) : about 80%. This gradually dropped to about 20% by 3,500 Ma. This coincides with the development of the first bacteria about 3,500 Ma. By the time of the development of photosynthesis (2,700 Ma), CO2 levels in the atmosphere were in the range of 15%. During the period from about 2,700 Ma to about 2,000 Ma, photosynthesis dropped the CO2 concentrations from about 15% to about 8%. By about 2,000 Ma free O2 was beginning to accumulate. This gradual reduction in CO2 levels continued to about 600 Ma at which point CO2 levels were below 1% and O2 levels had risen to more than 15%. 600Ma corresponds to the end of the Precambrian and the beginning of the Cambrian, the end of the cryptozoic and the beginning of the Phanerozic, and the beginning of oxygen-breathing life.
Carbon dioxide and free oxygen
The climate of the late Precambrian was typically cold with glaciation spreading over much of the earth. At this time the continents were bunched up in a supercontinent called Rodinia. Massive deposits of tillites are found and anomalous isotopic signatures are found which are consistent with the idea that the earth at this time was a massive snowball. Map of Rodinia at the end of the Precambrian after Australia and Antarctica rotated away from the southern hemisphere.
As the Proterozoic Eon drew to a close, the Earth started to warm up. By the dawn of the Cambrian and the Phanerozoic Eon, Earth was experiencing average global temperatures of about +22 °C. Hundreds of millions of years of ice were replaced with the balmy tropical seas of the Cambrian Period within which life exploded at a rate never seen before or after.
Precambrian climate
Qualitatively, the Earth's climate was varied between conditions that support large-scale continental glaciation and those which are extensively tropical and lack permanent ice caps even at the poles. The time scale for this variation is roughly 140 million years and may be related to Earth's motion into and out of galactic spiral arms (Veizer and Shaviv 2003). The difference in global mean temperatures between a fully glacial earth and ice free Earth is estimated at approximately 10 °C, though far larger changes would be observed at high latitudes and smaller ones at low latitudes. One key requirement for the development of large scale ice sheets is the arrangement of continental land masses at or near the poles. With plate tectonics constantly rearranging the continents, it can also shape long-term climate evolution. However, the presence of land masses at the poles is not sufficient to guarantee glaciations. Evidence exists of past warm periods in Earth's climate when polar land masses similar to Antarctica were home to deciduous forests rather than ice sheets.
Changes in the atmosphere may also exert an important influence over climate change. The establishment of CO2-consuming (and oxygen-producing) photosythesizing organisms in the Precambrian led to the production of an atmosphere much like today's, though for most of this period it was much higher in CO2 than today. Similarly, the Earth's average temperature was also frequently higher than at present, though it has been argued that over very long time scales climate is largely decoupled from carbon dioxide variations (Veizer et al. 2000). Or more specifically that changing continental configurations and mountain building probably have a larger impact on climate than carbon dioxide. Others dispute this, and suggest that the variations of temperature in response to carbon dioxide changes have been underestimated (Royer et al. 2004). However, it is clear that the preindustrial atmosphere with only 280 ppm CO2 is not far from the lowest ever occurring since the rise of macroscopic life.
Superimposed on the long-term evolution between hot and cold climates have been many short-term fluctuations in climate similar to, and sometimes more severe than, the varying glacial and interglacial states of the present ice age. Some of the most severe fluctuations, such as the Paleocene-Eocene Thermal Maximum, may be related to rapid increases in atmospheric carbon dioxide due to the collapse of natural methane reservoirs in the oceans (see methane clathrates). Severe climate changes also seem to have occurred during the course of the Cretaceous-Tertiary, Permian-Triassic, and Ordovician-Silurian extinction events; however, it is unclear to what degree these changes caused the extinctions rather than merely responding to other processes that may have been more directly responsible for the extinctions.
Controlling Factors
Geologic temperature record
Dendroclimatology
Historical climatology, the study of climate over human history (as opposed to earth's)
Cliwoc, Climatological database for the world's oceans (1759-1854)
Shen Kuo, 11th century Chinese scientist who realized the possibilities of paleoclimatology while observing ancient petrified bamboos buried underground in a northern, dry climate
Periodic Ice ages
Snowball Earth/Varangian glaciation (Hadean and Paleoproterozoic)
Permian-Triassic extinction event (Permian-Triassic)
Paleocene-Eocene Thermal Maximum (Paleocene-Eocene)
Younger Dryas/The Big Freeze (~11 000 BCE)
Holocene climatic optimum (~7000 BCE-3000 BCE)
Climate changes of 535-536 (535-536)
Medieval warm period (900-1300)
Little ice age (1300-1800)
Year Without a Summer (1816) Various notable climate-related events
History of the atmosphere
The earliest atmosphere of the Earth was probably stripped away by solar winds early in the history of the planet. These gases were later replaced by an atmosphere derived from outgassing from the Earth. Sometime during the late Archean Era an oxygen atmosphere began to develop from photosynthesizing algae.
Earliest atmosphere
Free oxygen did not exist until about 1,700 Ma and this can be seen with the development of the red beds and the end of the banded iron formations. This signifies a shift from a reducing atmosphere to an oxidising atmosphere. The early atmosphere and hydrosphere (up until about 2,000 Ma) were devoid of free oxygen. After photosynthesis developed, photoautotrophs began releasing O2.
The very early atmosphere of the earth contained mostly carbon dioxide (CO2) : about 80%. This gradually dropped to about 20% by 3,500 Ma. This coincides with the development of the first bacteria about 3,500 Ma. By the time of the development of photosynthesis (2,700 Ma), CO2 levels in the atmosphere were in the range of 15%. During the period from about 2,700 Ma to about 2,000 Ma, photosynthesis dropped the CO2 concentrations from about 15% to about 8%. By about 2,000 Ma free O2 was beginning to accumulate. This gradual reduction in CO2 levels continued to about 600 Ma at which point CO2 levels were below 1% and O2 levels had risen to more than 15%. 600Ma corresponds to the end of the Precambrian and the beginning of the Cambrian, the end of the cryptozoic and the beginning of the Phanerozic, and the beginning of oxygen-breathing life.
Carbon dioxide and free oxygen
The climate of the late Precambrian was typically cold with glaciation spreading over much of the earth. At this time the continents were bunched up in a supercontinent called Rodinia. Massive deposits of tillites are found and anomalous isotopic signatures are found which are consistent with the idea that the earth at this time was a massive snowball. Map of Rodinia at the end of the Precambrian after Australia and Antarctica rotated away from the southern hemisphere.
As the Proterozoic Eon drew to a close, the Earth started to warm up. By the dawn of the Cambrian and the Phanerozoic Eon, Earth was experiencing average global temperatures of about +22 °C. Hundreds of millions of years of ice were replaced with the balmy tropical seas of the Cambrian Period within which life exploded at a rate never seen before or after.
Precambrian climate
Qualitatively, the Earth's climate was varied between conditions that support large-scale continental glaciation and those which are extensively tropical and lack permanent ice caps even at the poles. The time scale for this variation is roughly 140 million years and may be related to Earth's motion into and out of galactic spiral arms (Veizer and Shaviv 2003). The difference in global mean temperatures between a fully glacial earth and ice free Earth is estimated at approximately 10 °C, though far larger changes would be observed at high latitudes and smaller ones at low latitudes. One key requirement for the development of large scale ice sheets is the arrangement of continental land masses at or near the poles. With plate tectonics constantly rearranging the continents, it can also shape long-term climate evolution. However, the presence of land masses at the poles is not sufficient to guarantee glaciations. Evidence exists of past warm periods in Earth's climate when polar land masses similar to Antarctica were home to deciduous forests rather than ice sheets.
Changes in the atmosphere may also exert an important influence over climate change. The establishment of CO2-consuming (and oxygen-producing) photosythesizing organisms in the Precambrian led to the production of an atmosphere much like today's, though for most of this period it was much higher in CO2 than today. Similarly, the Earth's average temperature was also frequently higher than at present, though it has been argued that over very long time scales climate is largely decoupled from carbon dioxide variations (Veizer et al. 2000). Or more specifically that changing continental configurations and mountain building probably have a larger impact on climate than carbon dioxide. Others dispute this, and suggest that the variations of temperature in response to carbon dioxide changes have been underestimated (Royer et al. 2004). However, it is clear that the preindustrial atmosphere with only 280 ppm CO2 is not far from the lowest ever occurring since the rise of macroscopic life.
Superimposed on the long-term evolution between hot and cold climates have been many short-term fluctuations in climate similar to, and sometimes more severe than, the varying glacial and interglacial states of the present ice age. Some of the most severe fluctuations, such as the Paleocene-Eocene Thermal Maximum, may be related to rapid increases in atmospheric carbon dioxide due to the collapse of natural methane reservoirs in the oceans (see methane clathrates). Severe climate changes also seem to have occurred during the course of the Cretaceous-Tertiary, Permian-Triassic, and Ordovician-Silurian extinction events; however, it is unclear to what degree these changes caused the extinctions rather than merely responding to other processes that may have been more directly responsible for the extinctions.
Controlling FactorsGeologic temperature record
Dendroclimatology
Historical climatology, the study of climate over human history (as opposed to earth's)
Cliwoc, Climatological database for the world's oceans (1759-1854)
Shen Kuo, 11th century Chinese scientist who realized the possibilities of paleoclimatology while observing ancient petrified bamboos buried underground in a northern, dry climate
