Climate+change+in+the+past+million+years+2010

Climate Change in the Past Million Years
The Earth's climate changed continuously throughout history. Starting from the glacial periods or "ice ages" to where ice retreated to the poles or melted entirely. Scientists have been able to predict the Earth's climate dating back decades to millions of years ago. They did this by analyzing a number of surrogate or a proxy, that measures climate through ice cores, boreholes, tree rings, glacier lengths, pollen remains, and ocean sediments, and by studying changes in the Earth's orbit around the sun.

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 * 1) **Changes in the Earth's orbit:** Changes in the earth's orbit as well as the earth's tilt affect the amount of sunlight received on the Earth's surface. These are thought to be the most significant causes of ice ages. This is the theory of Multin Milankovitch, a Serbian mathematician (1879-1958). The National Aeronautics and Space Administration's (NASA) Earth Observatory offers additional information about orbital variations.
 * 2) **Changes in the sun's intensity:** Changes occurring within the sun can affect the intensity of the sunlight. The intensity of the sunlight can cause either warming or cooling for stronger or weaker solar intensity. According to NASA reduced solar activity from the 1400s to the 1700s was likely the main reason of the “Little Ice Age” that resulted in a slight cooling of North America, Europe and other areas around the globe.
 * 3) **Volcanic eruptions:** Volcanoes can affect the climate because they can emit aerosols and carbon dioxide into the atmosphere. Volcanic aerosols tend to block sunlight and contribute to short term cooling, since they leave the atmosphere not long after they are emitted. The eruption of the Tambora Volcano in Indonesia in 1815 lowered global temperatures by as much as 5º F. Also New England describe it as 1816 as “the year without a summer.” Volcanoes also emit carbon dioxide (CO 2 ), a greenhouse gas, which has a warming effect. One theory to describe the increase of temperature is that volcanic eruptions from rapid sea floor spreading increased the CO 2 concentration. However, volcanoes may have raised pre-historic CO 2 levels and temperatures, human activities now emit 150 times as much CO 2 as volcanoes.
 * 4) **Changes in greenhouse gas concentrations: The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations. When global temperatures become warmer, carbon dioxide is released from the oceans. By increasing concentrations of carbon dioxide will enhance the greenhouse effect. When temperatures become cooler, CO2 enters the ocean and contributes to additional cooling. Through the past 650,000 we were able to track interglacial cycles. During warm interglacial periods, CO2 levels have been high and during cool glacial periods, CO2 levels have been low. An additional warm period has emerged in the past 100 years because of increasing emissions of greenhouse gases from human activities.  **

