Greenland ice sheet temperatures Vinther et al 2009

The neoglaciation ("renewed

glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...

") describes the documented cooling trend in the

Earth's climate Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorolog ...

during the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

, following the retreat of the

Wisconsin glaciation The Wisconsin glaciation, also called the Wisconsin glacial episode, was the most recent glacial period of the North American ice sheet complex, peaking more than 20,000 years ago. This advance included the Cordilleran Ice Sheet, which nucleated ...

, the most recent glacial period. Neoglaciation has followed the Hypsithermal or

Holocene Climatic Optimum The Holocene Climate Optimum (HCO) was a warm period in the first half of the Holocene epoch, that occurred in the interval roughly 9,500 to 5,500 years BP, with a thermal maximum around 8000 years BP. It has also been known by many other names ...

, the warmest point in the Earth's climate during the current

interglacial An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene i ...

stage, excluding the

global warming Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...

-induced temperature increase starting in the 20th century. The neoglaciation has no well-marked universal beginning: local conditions and

ecological inertia In ecology, an ecosystem is said to possess ecological stability (or equilibrium) if it is capable of returning to its equilibrium state after a perturbation (a capacity known as Ecological resilience, resilience) or does not experience unexpecte ...

affected the onset of detectably cooler (and wetter) conditions. Driven inexorably by the

Milankovitch cycle Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term was coined and named after the Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he pr ...

, cooler summers in higher latitudes of North America, which would cease to melt the annual snowfall completely, 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 Evelyn Chrystalla "E. C." Pielou (February 20, 1924 – July 16, 2016) was a Canadian statistical ecologist. Biography Pielou studied at the University of London, where she obtained her bachelor's degree in botany in 1951 and her PhD in 1962. F ...

. With the close of the "

Little Ice Age The Little Ice Age (LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. It was not a true ice age of global extent. The term was introduced into scientific literature by François E. Matthes in 1939. Mat ...

" (mid-14th to late 19th centuries), neoglaciation appears to have been reversed in the late 20th century, evidently caused by

anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Anthropogenic may also refer to things that have been generated by humans, as follows: * Human impact on the enviro ...

. Neoglaciation had been marked by a retreat from the warm conditions of the Climatic Optimum and the advance or reformation of

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

s that had not existed since the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...

. In the mountains of western North America, montane glaciers that had melted entirely reformed shortly before 5000 BP. The most severe part of the best documented neoglacial period, especially in Europe and the North Atlantic, is termed the "

Holocene climate reconstructions and glacial-advance records from western Canada

In North America, neoglaciation had ecological effects in the spread of

muskeg Muskeg (; ; , lit. ''moss bog'') is a peat-forming ecosystem found in several northern climates, most commonly in Arctic and boreal ecosystem, boreal areas. Muskeg is approximately synonymous with bogland, bog or peatland, and is a standard te ...

on flat, poorly drained land, such as the bed of recently drained

Lake Agassiz Lake Agassiz ( ) was a large proglacial lake that existed in central North America during the late Pleistocene, fed by meltwater from the retreating Laurentide Ice Sheet at the end of the last glacial period. At its peak, the lake's area wa ...

and in the

Hudson Bay Hudson Bay, sometimes called Hudson's Bay (usually historically), is a large body of Saline water, saltwater in northeastern Canada with a surface area of . It is located north of Ontario, west of Quebec, northeast of Manitoba, and southeast o ...

lowlands, in the retreat of grassland before an advancing forest border in the

Great Plains The Great Plains is a broad expanse of plain, flatland in North America. The region stretches east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include th ...

, and in shifting ranges of forest trees and diagnostic plant species (identified through

palynology Palynology is the study of microorganisms and microscopic fragments of mega-organisms that are composed of acid-resistant organic material and occur in sediments, sedimentary rocks, and even some metasedimentary rocks. Palynomorphs are the mic ...

). In

East Asia East Asia is a geocultural region of Asia. It includes China, Japan, Mongolia, North Korea, South Korea, and Taiwan, plus two special administrative regions of China, Hong Kong and Macau. The economies of Economy of China, China, Economy of Ja ...

, the start of neoglaciation coincided with a major weakening of the East Asian Summer Monsoon (EASM).

Notes

{{reflist, 2 Holocene History of climate variability and change

See also

Notes