89 The Greenhouse and Other Effects
Earth’s temperature depends on three things:
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Amount of sunlight received
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Most is ultraviolet with short wavelength
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About 2/3 is absorbed to warm the atmosphere
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Amount of sunlight reflected
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Mostly reflected as infrared radiation
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Degree to which the atmosphere retains heat
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•Water vapor, carbon dioxide, methane, nitrous oxides, and halocarbons absorb IR radiation
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Gasses act as “blanket” to retain heat in troposphere
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Three important greenhouse gases are shown symbolically in the image below: water vapor, carbon dioxide and methane.
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Greenhouse effect is a natural and necessary process.
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Earth would be 33o colder without it.
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All surface water would be frozen.
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Little life would exist.
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Natural effect is from water vapor.
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Absorption (trapping) of reflected energy by greenhouse gasses (carbon dioxide, methane, nitrous oxide, halocarbons)
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Enhances the greenhouse effect
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Carbon dioxide accounts for most of the anthropogenic greenhouse effect. It is the most studied.
Source: https://en.wikipedia.org/wiki/Greenhouse_gas#/media/File:Physical_Drivers_of_climate_change.svg
Volcanic Eruptions:
Ash from eruptions becomes suspended in the atmosphere, reflects sunlight having a cooling effect.
Mount Tambora, 1815 eruption contributed to cooling in North America and Europe.
Mount Pinatubo eruption in 1991 (June 12 – 16) counterbalanced global warming during 1991 and 1992.
11 major volcanic (flood basalt) events that affected Earth climate over 350 million years:
Source: Vincent E Courtillot, Paul R Renne, On the ages of flood basalt events, Comptes Rendus Geoscience, Volume 335, Issue 1, 2003, Pages 113-140. https://doi.org/10.1016/S1631-0713(03)00006-3
Human Impact: considered the most influential (primarily fossil fuels, deforestation, etc.)
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Mathematical models of climate can isolate human causes from solar and volcanic forcing of climate change.
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Models found that present warming greatly exceeds natural variability.
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Models agree with climate change predicted from greenhouse gas forcing.