The total amount of solar radiation varies by very small amounts. The energy emitted by the sun only varies by 1.3 W/m2. This change in solar radiation is related to the number of sunspots. Sunspots are darker areas on the sun’s surface. A sunspot develops where an intense magnetic field weakens the flow of gasses that transport heat energy from the sun’s interior. Sunspots appear dark because their temperature is lower than the surrounding area. Approximately every 11 years, the number of sunspots changes from a maximum number to a minimum number. The sun emits slightly more radiation during active periods of sunspots. Because the sunspots are suppressing heat, the heat flows to surrounding areas causing these regions to be brighter than normal, radiating more heat. While more sunspots may contribute to warmer global climate, fewer sunspots appear to be associated with a cooler global climate. About 300 years ago, there was a period of reduced solar activity. This was called the Little Ice Age. As tectonic plates move over geological timescales, landmasses are carried along to different positions and latitudes . These changes affect global circulation patterns of air and ocean water and the climate of the continents. One form of evidence for plate tectonics and an example of how plate tectonics affects climate is the location of coal mines. Coal mines were formed over millions of years ago in tropical areas, yet are found at higher latitudes today. You also learned in the Temperature over Time module that, since the industrial revolution, the Northern Hemisphere has warmed more than the Southern Hemisphere. This is because the Northern Hemisphere has a larger percentage of Earth’s landmass compared to the ocean than the Southern Hemisphere. Remember that landmasses warm faster than oceans due to the high heat capacity of the oceans. El Nino-Southern Oscillation (ENSO) is an oscillation of the ocean and atmosphere system in the tropical area of the Pacific Ocean that affects global weather. Normally the southeast trade winds blow across the tropical Pacific Ocean toward the west. Every 3 to 10 years, the southeast trade winds weaken, allowing the warm water to flow further eastward toward South America. This warmer current of water typically reaches the western coast of South America near Christmas and has become known to the Peruvian fishermen as El Nino (for the Christ child). El Nino is also known as the warm-water phase of the ENSO. El Nino causes the water temperature off of South America to be warmer. An El Nino warm-water phase changes global weather patterns. South America experiences wetter than average weather, while North America experiences mild but stormier winter weather. During an El Nino warm water phase, there are fewer and less intense hurricanes in the Atlantic Ocean because the rising warmer air over the eastern Pacific Ocean causes more wind shear and hurricanes are not able to form in the Caribbean Sea. Sometimes, after an El Nino phase subsides, a colder-than-normal water phase, known as La Nina.