Remember that landmasses warm faster than oceans due to the high heat capacity of the oceans. This is because the Northern Hemisphere has a larger percentage of Earth’s landmass compared to ocean than the Southern Hemisphere. You also learned in the Temperature Over Time module that, since the industrial revolution, the Northern Hemisphere has warmed more than the Southern Hemisphere. Coal mines were formed over millions of years ago in tropical areas, yet are found at higher latitudes today. One form of evidence for plate tectonics and an example of how plate tectonics affects climate is the location of coal mines. These changes affect global circulation patterns of air and ocean water and the climate of the continents. Movement of Crustal Platesĭigital Techtonic Activity Map of the Earth Source: NASAĪs tectonic plates move over geological timescales, landmasses are carried along to different positions and latitudes. About 300 years ago, there was a period of reduced solar activity. While more sunspots may contribute to warmer global climate, less sunspots appear to be associated with a cooler global climate. Because the sunspots are suppressing heat, the heat flows to surrounding areas causing these regions to be brighter than normal, radiating more heat. The sun emits slightly more radiation during active periods of sunspots. Sunspots appear dark because their temperature is lower than the surrounding area.Īpproximately every 11 years, the number of sunspots changes from a maximum number to a minimum number. A sunspot develops where an intense magnetic field weakens the flow of gases that transport heat energy from the sun’s interior. Sunspots are darker areas on the sun’s surface. This change in solar radiation is related to the number of sunspots. The energy emitted by the sun only varies by 1.3 W/m 2. The total amount of solar radiation varies by very small amounts. 2013 Credit: NASA/SDO/AIA/HMI/Goddard Space Flight Center Relatively cold years also followed other famous volcanic eruptions (such as the 1883 eruption of Krakatau also in Indonesia and 1991 eruption of Mount Pinatubo in the Philippines). Snow fell in the northeastern United States and Canada in June, causing regional losses of crops, food shortages, and increased mortality. This was possibly the largest known eruption in the history of human civilization. The year 1816, often referred to as the “year without a summer, occurred after the violent eruption of Indonesia’s Mount Tambora. Volcanic aerosols can block a percentage of sunlight and cause a cooling that may last for 1-2 years. Aerosols scatter incoming solar radiation, causing a slight cooling effect. They may also include soot, dust, salt crystals, bacteria, and viruses. Aerosols are liquids and solids that float around in the air. Volcanic eruptions discharge carbon dioxide, but they may also emit aerosols, such as volcanic ash or dust, and sulfur dioxide. Karymsky Volcano in Russia Source: Microsoft Clip Art The amount of solar radiation reaching the Northern Hemisphere at 65°N seems to control the advance and retreat of glaciers and ice sheets. The interplay of the three orbital cycles affects the amount of solar radiation received at different latitudes over the year. The figure above shows the alignment of each of the orbital changes to the glacial and interglacial periods. A relatively cool summer for the northern latitudes favors less melting of winter snow and glacier formation. These conditions for the northern latitudes favor somewhat higher temperatures, but also more water vapor in the air – causing more snowfall. Milankovitch proposed that glacial periods began when the three cycles align to favor an extended period of more solar radiation in the winter and less solar radiation in the summer at a latitude of 65°N. These fluctuations include changes in the shape (eccentricity) of Earth’s orbit every ~100,000 years, the tilt (obliquity) of Earth’s axis every ~41,000 years, and the wobbling (precession) of Earth’s axis about ~23,000 years. You have learned about these orbital changes in the Temperature over Time module. The Milankovitch Theory explains the 3 cyclical changes in Earth’s orbit and tilt that cause the climate fluctuations that occur over tens of thousands of years to hundreds of thousands of years. Milankovitch cycles over the past 1 000 000 years.
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