Climate change timeline
Theoretical reconstruction of ancient climates is important for understanding the evolution of the current climate and prehistoric human migrations and institutions, the impact of climate on mass extinctions, and current global warming.
Paleoclimatological evidence comes from the Earth and life sciences preserved within rocks, sediments, boreholes, ice sheets, tree rings, corals, shells, and microfossils combined with dating techniques. Popular aspects of the study include glaciations and rapid cooling events like the Younger Dryas, and the fast rate of warming during the Paleocene–Eocene Thermal Maximum.
We are currently within the Quaternary period (last 2.6 million years) of the geological Cenozoic Era which spans the last 66 million years. The Quaternary Period is divided into three epochs: the Pleistocene (from 2.6 million to 11.7 thousand years ago), the Holocene (11.7 thousand years ago), to the Anthropocene epoch starting in the 1950s (sometimes dated from the beginning of the Agricultural Revolution 12,000–15,000 years ago, but more often to the onset of the Great Acceleration in human population and resource consumption that occurred alongside a peak in nuclear fallout during atomic bomb testing in the 1950s).
The Quaternary is characterized by recurring ice ages (there have been 40-50) with continental glaciers moving as far from the poles as 40 degrees latitude. Freezing lasts, on average, about 80,000 years and is accompanied by falls in sea level as ice locks up water at the poles, opening up land bridges. Warmer periods last, on average, about 15,000 years as continental shelves are flooded. We are currently living through an interglacial period that started about 11,700 years ago.
Serbian geophysicist and astronomer Milutin Milanković hypothesized in the 1920s that Earth’s variation in eccentricity, axial tilt, and precession resulted in cyclical variation in the solar radiation reaching the Earth, and that it was this orbital forcing that strongly influenced the Earth’s climatic patterns. These regular patterns are now known as Milanković cycles.
Major ecological changes during the Quaternary are the consequence of climate change, volcanic eruptions, and human influence over the last 70 or so years.
14,690 to 12,890 – Bølling–Allerød interstadial
an abrupt warm and moist interstadial period that occurred during the final stages of the last glacial period. It began with the end of the cold period known as the Oldest Dryas, and ended abruptly with the onset of the Younger Dryas, a cold period that reduced temperatures back to near-glacial levels within a decade.
12,900 to 11,700 – Younger Dryas
the most recent and longest of several interruptions to the gradual warming of the Earth’s climate since the severe Last Glacial Maximum about 27,000 to 24,000 years BP after ice started to recede around 20,000 BP. Named from the alpine-tundra wildflower Dryas octopetala whose leaves are occasionally abundant in late glacial, often minerogenic-rich sediments, such as the lake sediments of Scandinavia. The change was relatively sudden, over decades, the temperatures in Greenland falling by 4 to 10°C (7.2 to 18°F) with advance of glaciers and drier conditions over much of the temperate Northern Hemisphere. Possibly caused by a decline in the strength of circulation in the the Atlantic currents that transport warm water from the Equator towards the North Pole, in turn probably caused by an influx of fresh, cold water from North America to the Atlantic. In the Southern Hemisphere and some areas of the Northern Hemisphere, such as southeastern North America, only a slight warming occurred.
9000-5000 – Holocene Climate Optimum (HCO)
was a warm period with a thermal maximum around 8000 years BP. This warm period was followed by a gradual decline until about two millennia ago
c. 3000 – eruption of Icelandic volcano Mt Hekla (Hekla 3, or H3)
(A regional phenomenon) the atmospheric volcanic ash cooling northern parts of the globe for a few years. Traces of this eruption are found in Scottish peat bogs, and in Ireland a study of tree rings dating from this period has shown negligible tree ring growth for a decade.
250 BCE to 400 CE – Roman Warm Period
(A regional phenomenon) a period of unusually warm weather in Europe and the North Atlantic. This is supported by pollen analysis on the Iberian Peninsula and ice on alpine glaciers. Theophrastus (371 – c. 287 BC) wrote that date trees, as today, could grow in Greece but could not set fruit there. This suggests that South Aegean mean summer temperatures in the 4th and 5th centuries BCE were within a degree of modern temperatures. That and other literary fragments from the time confirm that the Greek climate then was basically the same as it was around 2000 CE. Dendrochronological evidence from wood found at the Parthenon indicates variability of climate in the 5th century BCE, which resembles the modern pattern of variation. Tree rings from the Italian Peninsula in the late 3rd century BC indicate a period of mild conditions in the area at the time of Hannibal’s crossing of the Alps with elephants (218 BCE). Roman occupation of north-western Europe corresponded with this dry era, sometimes called the Roman Climatic Optimum, which lasted from about 300 BCE to 300 CE with hot, dry summers and winter rain (grapes were grown in southern Britain) as intensive Roman production systems replaced Celtic multiple-species agriculture and pastoralism. This faltered around 350 CE with the onset of cooler conditions (late spring frosts, damp summers, storm damage, disease and blight) in NW Europe and conditions worsened in 450 CE with flooding, soil erosion and nutrient leaching.
365 – E Mediterranean Tsunami
The 365 Crete earthquake occurred at about sunrise on 21 July 365 in the Eastern Mediterranean with an assumed epicentre near Crete. Geologists estimate the undersea earthquake to have been a magnitude 8.0 or higher. It caused widespread destruction in the central and southern Macedonia (modern Greece), Africa Proconsularis (northern Libya), Egypt, Cyprus, Sicily, and Hispania (Spain). On Crete, nearly all towns were destroyed. The earthquake was followed by a tsunami which devastated the southern and eastern coasts of the Mediterranean, particularly Libya, Alexandria, and the Nile Delta, killing thousands and hurling ships 3 km (1.9 mi) inland. The quake left a deep impression on the late antique mind, and numerous writers of the time referred to the event in their works. In the summer of 365, the port of Alexandria in Egypt was hit by a powerful tsunami that had traveled across the eastern Mediterranean, generated by a sea-floor earthquake near Turkey. Italy, Greece, and Turkey were among the other places impacted. Alexandria was the main Roman trading hub and port through which its wheat, grown in the Nile valley, would pass (wheat was also imported to Rome from Carthage). Though not strictly a climate event the tsunami was a natural disaster with a deep impact on the ancient world.
950-1250 – Medieval Climatic Anomaly (Medieval Warm Period)
(a regional phenomenon) a time of warm climate in the North Atlantic region and probably related to warming elsewhere, although some regions were colder, such as the tropical Pacific. Average global mean temperatures were similar to early-mid-20th-century warming. Possible causes include increased solar activity, decreased volcanic activity, and changes to ocean circulation. It is thought that between c. 950 and c. 1100 was the Northern Hemisphere’s warmest period since the Roman Warm Period.
1300-1850 – Little Ice Age
(a regional phenomenon) not a true Ice Age but three cold intervals, one beginning about 1650, another about 1770, and the last in 1850, each separated by intervals of slight warming. The Intergovernmental Panel on Climate Change Third Assessment Report considers the timing and areas affected by the Little Ice Age and suggests largely independent regional climate changes rather than a globally synchronous increased glaciation. There was only modest cooling in the Northern Hemisphere. Causes possibly include cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, variations in Earth’s orbit and axial tilt (orbital forcing), inherent variability in global climate, and even decreases in the human population (for example from the Black Death and the colonization of the Americas).
El Niño Southern Oscillation (ENSO)
is an irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics. El Niño events cause short-term (approximately 1 year in length) spikes in global average surface temperature while La Niña events cause short term cooling. The warming phase of the sea temperature is known as El Niño and the cooling phase as La Niña. The Southern Oscillation is the accompanying atmospheric component, coupled with the sea temperature change: El Niño is accompanied by high air surface pressure in the tropical western Pacific and La Niña with low air surface pressure there. The two periods last several months each and typically occur every few years with varying intensity per period
What Causes an Ice Age?
Atlas Pro – 2020 – 13:43
How Bad Was The Younger Dryas? Causes-Megafauna-Civilization
Stefan Milo – 2019 – 28:14
The Geography of the Ice Age
Atlas Pro – 2020 – 15:27
First published on the internet – 1 March 2019
. . . minor edit 5 January 2022