Plate tectonics, supercontinents, and massive vol-canism can cause climate variations on timescales of millions to billions of years. Many other variables contribute to climate variations that operate on shorter-term timescales, many of which are more observable. Variations in Earth's orbit around the Sun exhibit cyclic variations that alternately make Earth's climate warmer and colder at timescales ranging from 100,000 years down to 11,000 years. These cycles, known as Milankovitch cycles, have been convincingly shown to correlate with advances and retreats of the glaciers in the past few million years, and have operated throughout Earth history.
Changes in ocean circulation patterns caused by changes in seawater salinity and many other factors can dramatically change the pattern of heat distribution on the planet and global climate. Many ocean currents are driven by differences in temperature and salinity of ocean waters; these currents form a pattern of global circulation known as thermohaline circulation. Changes in patterns of thermohaline circulation can occur quite rapidly, perhaps even over 5-10 years, suddenly plunging warm continents into long, icy winters or warming frozen, ice-covered landscapes. Other changes in the ocean-atmosphere system also cause the local climate to change on 5-10-year timescales. The most dramatic of these is the El Nino-Southern Oscillation, which strongly affects the Pacific and the Americas but has influences worldwide.
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