TABLE 1 Climate and Related Conditions at Selected Times in the Past

Approximate Date

Climate and Related Conditions

10,000 BP

End of glaciation, glacier retreat, rapid rise of sea level, wet period North Africa and equatorial takes

8,000 – 7,000 BP

Hypsithermal — warmer, drier Sahara

6,000 BP

Rate of sea level rise slowing, Strait of Dover open

5,000 BP

Brief cold period, Stone Age

4,500 BP

Increasing aridity in drylands, warmest post-glacial period

1 AD

Continuing warm in Europe

800 – 1000 AD

Warmer, Norse in Greenland, medieval warm period

1500 AD

Little Ice Age (1300 – 1700 AD) Europe

1800 AD

Temperature somewhat lower than present

Present

Warmer than late 19th century

NOTE: BP: before the present.

SOURCE: Data from Lamb (1982) and Jäger and Barry (1990).

seconds to millennia, but also slow or punctuated evolutionary changes in biota are a continuing phenomenon. Similarly, climate as well as landscape and vegetation has fluctuated greatly during the brief interval of human occupance of the earth (Table 1). Thus the impact of population numbers or of population and technological change cannot be evaluated in the absence of some knowledge of the behavior of the ''natural'' scene. Understanding the vicissitudes of the natural system is particularly important in evaluating efforts at remediation of human impacts and in assessing the degree to which particular impacts are likely to be manageable if not reversible within varying periods of time. Temporal and spatial scales, however, are interrelated. For example, as small parcels of land are changed within a forest, upon abandonment the surrounding forest may readily provide seed for regeneration. In contrast, extensive cutting of forests for agriculture may leave only small refuges of original plants and animals, reducing the likelihood of regeneration of some of the biota and increasing the duration of transformation. Human beings have altered the land at varying rates and over vastly different areas. Many of these changes can be seen in the historical record.



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