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 an area, 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 meteorological ...

during the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

, following the retreat of the

Wisconsin glaciation The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cord ...

, the most recent glacial period. Neoglaciation has followed the hypsithermal or Holocene Climatic Optimum, the warmest point in the Earth's climate during the current interglacial stage, excluding the

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

-induced temperature increase starting in the 20th century. 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 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 Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he hypot ...

, 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. With the close of the " Little Ice Age" (mid-14th to late 19th centuries), neoglaciation appears to have been reversed in the late 20th century, evidently caused by anthropogenic

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

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

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 gre ...

. In the mountains of western North America, montane glaciers that had completely melted reformed shortly before 5000 BP.Pielou 1991:291; geomorphology of

glacial moraine A moraine is any accumulation of unconsolidated debris (regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice she ...

s suggest that mountain glaciers in

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

have advanced and receded twice more recently, with advances peaking about 2800 BP and 300 BP (noting G.H. Denton and W. Karlen, ""Holocene climatic variations— their pattern and possible cause", ''Quaternary Research'' 3 1973:155-205), and J.M. Ryder and B. Thomson, "Neoglaciation in the southern Coast Mountains of British Columbia: chronology prior to the Late Neoglacial Maximum", ''Canadian Journal of Earth Sciences'' 23 1986:273-87. The most severe part of the best documented neoglacial period, especially in Europe and the North Atlantic, is termed the " Little Ice Age". Holocene climate reconstructions and glacial-advance records from western Canada

Holocene climate reconstructions and glacial-advance records from western Canada

In North America, neoglaciation had ecological effects in the spread of muskeg on flat, poorly drained land, such as the bed of recently drained

Lake Agassiz Lake Agassiz was a large glacial lake in central North America. Fed by glacial meltwater at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined. First postulated in 1823 by William H. Keating, i ...

and in the Hudson Bay lowlands, in the retreat of grassland before an advancing forest border in the Great Plains, and in shifting ranges of forest trees and diagnostic plant species (identified through

palynology Palynology is the "study of dust" (from grc-gre, παλύνω, palynō, "strew, sprinkle" and ''-logy'') or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposit ...

Notes

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

See also

Notes