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Lecture 12b Recent Warming
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The Main Evidence The Global Temperature Record: 1860 - today
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The Global Historical Climate Network (GHCN)
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Global Mean Temperature – Instrumental Period Source: http://www.cru.uea.ac.uk/cru/data/temperature /http://www.cru.uea.ac.uk/cru/data/temperature / Temperature Anomaly ( o C) Note the strong positive anomalies 1998, 2010
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Instrumental Record – Global Mean Temperature Global mean temperature has risen approximately 0.6 to 1.0 °C in last 100 years Most of the increase occurred in two stages: 1910-1940 and 1975 – today Global temperature changed little in period 1940 - 1975 Global temperature changed little in period 1940 - 1975
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Causes of 20 th -Century Warming Recall: Large increases in greenhouse gas concentrations, esp. CO 2 Recall: Large increases in greenhouse gas concentrations, esp. CO 2 Seems likely that this is main cause Seems likely that this is main cause
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A Thorny Question Surface temperature record is much “noisier” than CO 2 record. Why? Answer: Surface temp. has more influences than atmospheric CO 2.
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Some Natural Factors Influencing Surface Temp Natural variability Example: El Niño/La Niña cycle Example: El Niño/La Niña cycle External forcing Solar flux variations (more later) Solar flux variations (more later) Particles from volcanic eruptions Particles from volcanic eruptions
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“Normal” Temperatures in Equatorial Pacific “Anomaly” is the deviation from the average.
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El Niño Temperatures
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El Niño In El Niño years, surface temperature is slightly higher than normal
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Global Mean Temperature – Instrumental Period Source: http://www.cru.uea.ac.uk/cru/data/temperature /http://www.cru.uea.ac.uk/cru/data/temperature / 1998 El Niño
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Another sources of “noise” Volcanic eruptions (see next slide)
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Troposphere Stratosphere Incoming Sunlight Volcano Formation of Particles Transport by Winds Reflection Photochemistry Another Source of Noise: Volcanoes
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Volcanoes Effect on Global Temperature A large volcanic eruption can cool the Earth for a few years Example: Mt. Pinatubo eruption in Philippines in summer of 1991
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Global Mean Temperature – Instrumental Period Source: http://www.cru.uea.ac.uk/cru/data/temperature /http://www.cru.uea.ac.uk/cru/data/temperature / Mt. Pintubo eruption
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Bottom Line Fluctuations are to be expected due to natural processes. However, recent rising trend can only be explained by increased greenhouse effect
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Another Interesting Question Was the rate of warming during the past century unusual? To answer, need proxy data. Main types: tree rings, ice cores http://www.ncdc.noaa.gov/paleo/globalwar ming/proxydata.html http://www.ncdc.noaa.gov/paleo/globalwar ming/proxydata.html http://www.ncdc.noaa.gov/paleo/globalwar ming/proxydata.html http://www.ncdc.noaa.gov/paleo/globalwar ming/proxydata.html
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Temperatures of Past Millennium
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Answer to Question The warming trend of the past 100 years appears to be unusually large when compared to previous 9 centuries
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