Neoglaciation
Encyclopedia
The neoglaciation describes the documented cooling trend in the Earth's climate
Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time, and is a branch of the atmospheric sciences...

 during the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...

, following the retreat of the Wisconsin glaciation
Wisconsin glaciation
The last glacial period was the most recent glacial period within the current ice age occurring during the last years of the Pleistocene, from approximately 110,000 to 10,000 years ago....

, the most recent glacial period. Neoglaciation has followed the hypsithermal or Holocene Climatic Optimum
Holocene climatic optimum
The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...

, the warmest point in the Earth's climate during the current interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...

 stage. The neoglaciation has no well-marked universal beginning: local conditions and ecological inertia affected the onset of detectably cooler (and wetter) conditions.

Driven inexorably by the Milankovitch cycle, cooler summers in higher latitudes of North America, which would cease to completely melt the annual snowfall, were masked at first by the presence of the slowly disappearing continental ice sheets, which persisted long after the astronomically calculated moment of maximum summer warmth: "the neoglaciation can be said to have begun when the cooling caught up with the warming", remarked E. C. Pielou
E. C. Pielou
Evelyn Chrystalla Pielou is a statistical ecologist. She began her career as a researcher for the Canadian Department of Forestry and the Canadian Department of Agriculture...

. With the close of the "Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

" (mid 14th to late 19th centuries), neoglaciation appears to have been stalled in the late 20th century by anthropogenic global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

. Whether it has been temporarily or semi-permanently stalled, neoglaciation has been marked by a retreat from the warm conditions of the Climatic Optimum
Holocene climatic optimum
The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...

 and the advance or reformation of glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...

s that had not existed since the last ice age
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

. In the mountains of western North America, montane glaciers that had completely melted reformed shortly before 5000 BP
Before Present
Before Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...

. The most severe part of the best documented neoglacial period, especially in Europe and the North Atlantic, is termed the "Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

".

In North America, neoglaciation had ecological effects in the spread of muskeg
Muskeg
Muskeg is an acidic soil type common in Arctic and boreal areas, although it is found in other northern climates as well. Muskeg is approximately synonymous with bogland but muskeg is the standard term in Western Canada and Alaska, while 'bog' is common elsewhere. The term is of Cree origin, maskek...

 on flat, poorly-drained land, such as the bed of recently-drained Lake Agassiz
Lake Agassiz
Lake Agassiz was an immense glacial lake located in the center of North America. Fed by glacial runoff at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined, and it held more water than contained by all lakes in the world today.-Conception:First...

 and in the Hudson Bay
Hudson Bay
Hudson Bay , sometimes called Hudson's Bay, is a large body of saltwater in northeastern Canada. It drains a very large area, about , that includes parts of Ontario, Quebec, Saskatchewan, Alberta, most of Manitoba, southeastern Nunavut, as well as parts of North Dakota, South Dakota, Minnesota,...

 lowlands, in the retreat of grassland before an advancing forest border in the Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...

, and in shifting ranges of forest trees and diagnostic plant species (identified through palynology
Palynology
Palynology is the science that studies contemporary and fossil palynomorphs, including pollen, spores, orbicules, dinoflagellate cysts, acritarchs, chitinozoans and scolecodonts, together with particulate organic matter and kerogen found in sedimentary rocks and sediments...

).

The view that neoglaciation is ending in present times, is assumed by those who identify the most recent climate changes and global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 as the onset of a new period in Earth history, speculatively calling it the "Early anthropocene", as a coming geological age dominated by the effects of Homo sapiens.
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