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Lecture 12b

This lecture discusses the significant rise in global mean temperatures over the past century, focusing on the historical climate record from 1860 to today. It highlights the main stages of warming, the impact of greenhouse gas emissions, and the influence of natural variability such as the El Niño/La Niña cycle. The analysis of the instrumental temperature record and the effects of volcanic eruptions on climate are also covered. The lecture concludes that the recent warming trend is distinct from past climate fluctuations, underscoring the role of the greenhouse effect.

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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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