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Geoengineering

Author(s): Goudie AS, Cuff DJ, Keith DW

Published: November, 2001

Publisher: Encyclopaedia of Global Change (Oxford University Press, USA)

Tags: Overview

URL: http://www.oup.com/us/brochure/95108256/sample.articles/climate/?view=usa

Abstract: The Earth undergoes changes in climatic conditions that are observable in a variety of instrumental and other records over time scales ranging from seasons to many millions of years. These changes result from periodic and random adjustments in the intensity and global distribution of solar radiation and the way this energy is redistributed. Atmospheric, oceanic, and cryospheric processes are responsible for this redistribution. Periods in Earth history during which ice is present at high latitudes, and climate changes exhibit pronounced shifts between relatively colder and warmer states, are termed ice ages. The present ice age commenced approximately 2.5 million years ago and its occurrence defines the Quaternary period of Earth history. Over long time scales (millions of year), the arrangement of tectonic plates plays a critical role in determining the extent of the cryosphere and whether an ice age state will occur. When ice ages such as the present one do occur, a series of long-term (tens of thousands of years) shifts between glacial and interglacial conditions results, and these shifts may be further subdivided into short-duration stadial and interstadial events. There is also evidence for climate changes of shorter duration (millennial, centennial, and decadal); these were pronounced in amplitude during the last glacial period, and are also present but more subtle in their extent during the present interglacial period. External factors such as quasiperiodic changes in the Earth’s orbit around the Sun play a significant role in influencing long-term changes. A combination of internal and external factors is responsible for shorter-duration changes, including variations in solar emissions, volcanic eruptions, and shifts in greenhouse gas concentrations. During the past two centuries, anthropogenic activity has resulted in large increases in the atmospheric greenhouse gas content, which has caused a detectable increase in global temperatures and are predicted to continue to increase for many decades before the climate system reaches a new equilibrium. There is considerable difficulty in separating the intrinsic steady-state equilibrium variability of climate (climate variation) from actual climatic changes, particularly over shorter (namely, human) time scales.


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