| Summary: | Instructions Accompanying New Domestic devices are tedious. So, uninstructed, we plunge into assembling the device … and the likely result is all too familiar. By analogy, a basic understanding of the climate system and the forces influencing it will shed more light on later chapters. The climate system has many interacting parts, encompassing the linkages between atmosphere, oceans, land, and ice surfaces. The atmosphere and oceans are the prime global distributors of that part of incoming solar energy that Earth retains in the form of heat, much of which is then re- expressed as water vapor, wind, and ocean currents. As part of the Earth system, the world’s climate is always changing. The internal dynamics of the climate system are complex and regionally distinctive, and include, on shorter time scales, chaotic behavior. Meanwhile, larger forces are at work. As continents coalesce and then drift apart; as massive mountain ranges get pressed skyward; as Earth’s elliptical orbit around the sun alternates between greater and lesser rotundity; as both the tilt and wobble of the planet’s axis vary; as solar sunspots come and go; as fluctuations occur in the great ocean- based regional climatic cycles (the Pacific’s El Niño Southern Oscillation, the Indian Ocean Dipole Oscillation, the North Atlantic Inter- Decadal Oscillation, and others); and as volcanic eruptions enshroud the lower atmosphere— so the world’s climate varies on time- scales ranging from tens of millions of years to just several years. The main engine of the climate system, the atmosphere, is made up of many local circulation subsystems, often interacting with (or “coupled” with) the oceans. At a regional scale, different combinations of local circulation systems account for changes in climate, such as the decline in rainfall in Mesopotamia during the third millennium B.C.E., or the southward encroachment of the Arctic polar vortex that imposed the Big Freeze on much of the north eastern USA in the 2013– 2014 winter.
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