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Lecture 12b

Lecture 12b. Recent Warming. The Main Evidence. The Global Temperature Record: 1860 - today. The Global Historical Climate Network (GHCN). Global Mean Temperature – Instrumental Period. Note the strong positive anomalies 1998, 2010. Temperature Anomaly ( o C).

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Lecture 12b

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  1. Lecture 12b Recent Warming

  2. The Main Evidence The Global Temperature Record: 1860 - today

  3. The Global Historical Climate Network (GHCN)

  4. Global Mean Temperature – Instrumental Period Note the strong positive anomalies 1998, 2010 Temperature Anomaly (oC) Source: http://www.cru.uea.ac.uk/cru/data/temperature/

  5. 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

  6. Causes of 20th-Century Warming • Recall: Large increases in greenhouse gas concentrations, esp. CO2 • Seems likely that this is main cause

  7. A Thorny Question • Surface temperature record is much “noisier” than CO2 record. Why? • Answer: Surface temp. has more influences than atmospheric CO2 .

  8. Some Natural Factors Influencing Surface Temp • Natural variability • Example: El Niño/La Niña cycle • External forcing • Solar flux variations (more later) • Particles from volcanic eruptions

  9. “Normal” Temperatures in Equatorial Pacific “Anomaly” is the deviation from the average.

  10. El Niño Temperatures

  11. El Niño • In El Niño years, surface temperature is slightly higher than normal

  12. Global Mean Temperature – Instrumental Period 1998 El Niño Source: http://www.cru.uea.ac.uk/cru/data/temperature/

  13. Another sources of “noise” • Volcanic eruptions (see next slide)

  14. Another Source of Noise: Volcanoes Incoming Sunlight Reflection Transport by Winds Photochemistry Formation of Particles Stratosphere Troposphere Volcano

  15. 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

  16. Global Mean Temperature – Instrumental Period Mt. Pintubo eruption Source: http://www.cru.uea.ac.uk/cru/data/temperature/

  17. Bottom Line • Fluctuations are to be expected due to natural processes. • However, recent rising trend can only be explained by increased greenhouse effect

  18. 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/globalwarming/proxydata.html

  19. Temperatures of Past Millennium

  20. 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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