Chapter 14 Past and Present Climates Koppen scheme Little Ice Age Maunder Minimum Medieval Warming Period Milankovitch cycles Moist subtropical and midlatitude climates Obliquity Paleoclimate Pangea Permafrost Plate tectonics Polar climates Precession Radiocarbon dating Severe mid latitude climates Subartctic climate Taiga Tropical humid climates Weak Sun Paradox Younger Dryas Key Terms Boreal forests Climate Climographs Dendrochronology Dry climate zones Eccentricity Glacier Historical climate Humid continental Ice ages Ice sheets Isotopes Summary Climate varies from place to place and over time The five basic climate controls are latitude elevation topography proximity to large bodies of water and prevailing atmospheric circulation Climate classifications are developed to organize the complex and varied climates of the world The Koppen based climate classification is the most wildly used scheme for describing today s climates The most recent Koppen Geiger scheme has six main groups each designated with a letter tropical moist A dry B moist with mild winters C moist with sever winters D and Polar E Through a variety scientific evidence climatologists have been able to determine the past climates of Earth This evidence includes historical records tree rings pollen deposits air and dust trapped in ice sheets sediments found on the ocean floor and fossils This evidence indicates that during most of the past 500 million years the Earth enjoyed warmer and more congenial climate than we experience today This mild climate has been repeatedly punctuated by cooler periods including ice ages Scientists have proposed several different mechanisms by which Earth s climate can change naturally on a variety of time scales Emissions from volcanic eruptions can cool the Earth s atmosphere for a few years Asteroids and comets can crash into the Earth causing mass extinctions and the dawn of new eras in Earth s biological and climatic histories The Sun s energy output can vary over short and very long time scales The Earth s orbit also varies on time scales of tens of thousands of years altering the distribution and amount of solar energy reaching Earth The motions of the continents over millions of years have probably triggered eras of worldwide warmth as well as ice ages Changes in the ocean circulation can help cause abrupt climate change during time periods of a decade or less For the past 20 000 years records of climate are rather complete Over this time span the Earth s climate change from a period of extreme glaciation to a warmer interglacial period Alternating episodes of relatively cooler and warmer temperatures have characterized the past several thousand years including the Younger Dryas about 11 000 years ago and the more recent Little Ice Age 1400 1850 in and near Europe Changes in ocean circulation and solar output may explain these oscillations in climate Recent increases in global temperature may be a result of human activity
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