Paleoclimate: The History of Climate Change

By: Staff Reporter
Present discussions on climate change are based on data that is gathered from studies conducted on coral cores, ice cores, tree rings, pollen, sediment from oceans and lakes, varves, pack rat middens and other indicators that are present in nature. Once past climates are determined it is possible to draw inferences and project changed regimes.
Weather n Climate

Paleoclimatology is the study of climate prior to the widespread availability of records of temperature, precipitation and other instrumental data. Scientists find it particularly interesting to study the last few thousand years as it is the best dated, best sampled part of the past climatic record and can help us establish the range of natural climatic variability in a period prior to global scale human influence. Environmental recorders are used to estimate past climatic conditions and thus extend our understanding beyond the last hundred years of instrumental record. Proxy records of climate have been preserved in tree rings, locked in the skeletons of tropical coral reefs, extracted as ice cores from glaciers and ice caps, and buried in laminated sediments from lakes and ocean.

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One of the most detailed chronologies for the past few thousand years lies in varves, the annual layers of silt and clay deposited on the bottoms of lakes and ponds that are subject to freezing in winter and thawing in summer. About 13,700 years are represented in the varve records of Scandinavia, where the oldest varves are in the south and the newest in the north, permitting a chronology of the last glacial recession.

PROXY EVIDENCE

Reconstruction of climates prior to human history through abundant and sometimes contradictory evidence indicates marked changes in climate since the creation of earth. Plant and animal fossils in various sedimentary deposits are the primary clues to duration and geographical extent of temperature and moisture conditions since the beginning of the Cambrian Period when life forms began to develop rapidly and the free oxygen content of the atmosphere increased. Fossils form the primary data of paleoclimatology. Inorganic deposits of alluvial, aeolian, glacial or volcanic origin also reflect past climates, although they often contain organic materials that enhance interpretation. Erosional landforms offer corroborative evidence of climatic processes such as flooding, glaciation, or wind action. Shoreline features indicate changing lake and ocean levels in response to climatic fluctuations.

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CLIMATIC CYCLES

Although it is clear that climatic fluctuations have occurred in historic times, but the regularity of climatic cycles is far less certain. Even the well recognised daily and seasonal cycles vary in length by large percentages. Daily maximums of temperature, for example, rarely succeed one another at intervals of exactly 24 hours. The annual cycle often has seasons that are early or late; January and July are by no means always the extreme months in middle and high latitudes. The reversal of the monsoon in southern and eastern Asia is generally regarded as an annual phenomenon, but it occurs at widely differing dates. Analyses of both proxy and instrumental data have suggested a great number of supposed cycles, few of which have a dependable regularity. Most are barely distinguishable from chance anomalies and should be termed rhythms or quasi-periodicities. Evaluations of hypothetical climatic cycles often are more productive when cause and effect are treated together. The relentless search for periodicities in solar activity, earth sun relations, composition of the atmosphere, and other phenomena that may influence climate will no doubt continue as long as there is remote hope of identifying cycles, which would be valuable aids to climate forecasting.

A full understanding of climate systems and explanations of past climates logically lead to prediction of future climates. Most climate change researchers agree that the earth is currently in an interglacial epoch, but few venture predictions of the dates of the next ice age. As always, we should expect years in which the weather departs from the ‘normal’. However volcanic eruptions, geomorphic processes, or some other suspected or unknown cause of climatic change may produce even more marked climatic fluctuations in the next few centuries than have occurred in the past. The uncertainty becomes much greater when extended in time and space.

Extract: NOAA. gov, General Climatology by Howard J Critchfield

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