Climate has not remained the same throughout time. Many natural phenomena have had their effects on the Earth's climate on different timescales: on tectonic scales are the slow movements of the Earth's continents—a process called plate tectonics (discussed in greater detail in chapter 3), on orbital scales are the orbital variations of the Earth, its eccentricity, tilt, and wobble (discussed in chapter 5); on millennial scales, ice ages, and on centennial scales, droughts.
Because these natural cycles can be occurring independently and take different amounts of time to occur—tectonic scales have occupied periods over the past 300 million years; orbital scales over the past 3 million years; millennial scales over the past 50,000 years, and centennial scales over the past 1,000 years—the climate system can be very complex because all these climate processes interact. In general, the shorter the timescale, the more impact a process has on a local scale
The thermohaline circulation, or ocean conveyor belt, is the principal mechanism for transporting heat from the Tropics to the polar regions. If the conveyor belt were to shut down, it could cause Europe to enter a severe cold period and disrupt climate around the world.
(modeled after IPCC)
(such as a drought). The longer the timescale, the bigger impact the process has on a global scale (such as plate tectonics).
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