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Historical Perspectives on Climate Change Research

Historical Perspectives on Climate Change Research. Primary Source: IPCC WG-I Chapter 1 - Historical Overview of Climate Change Science. The Scientific Basis. 1. Hypothesis testing - Should be subject to peer analysis & review - Can it be shown, in principle, to be false?

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Historical Perspectives on Climate Change Research

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  1. Historical Perspectives onClimate Change Research Primary Source: IPCC WG-I Chapter 1 - Historical Overview of Climate Change Science

  2. The Scientific Basis 1. Hypothesis testing - Should be subject to peer analysis & review - Can it be shown, in principle, to be false? - Can it provide predictions (tests)? Basis for scientific progress - builds on previous work - self-correcting • For IPCC: Key questions • Has it been rigorously tested? • Did it appear in the peer-reviewed literature? • Did it build on the existing research record where appropriate? • What are the uncertainties?

  3. How Do Climate Scientists Conduct Experiments? • There is only one planet. • How can one test hypotheses? Observed behavior (e.g., short-term climate perturbations, like volcanic emissions) Simulation models Fundamental theory

  4. Rigorous Review is Essential! Growth in the Peer-Reviewed Literature

  5. Rigorous Review is Essential! Growth in the Peer-Reviewed Literature

  6. What Determines Earth’s Climate? Earth’s Orbit

  7. Earth’s Orbital Parameters Vernal Equinox (~ March 21) Aphelion (~ July 5) Perihelion (~ Jan 3) Why is Iowa colder in January?

  8. Earth’s Orbital Parameters b a Eccentricity = SQRT(a2 - b2)/a ; for circle, = 0 Longitude of perihelion (one choice: angle from NH vernal equinox) Tilt of rotation axis (obliquity)

  9. What Determines Earth’s Climate? Earth’s Albedo Earth’s Orbit Earth’s Emissions

  10. The Greenhouse Effect

  11. The Greenhouse Effect: Early Discoveries Edme Marriotte (1620-1684): Sun’s heat passes through glass, other heat does not (1681). (www.nndb.com) Horace Bénédict de Saussure (1740-1799): Air in mountains does not trap heat as much as air in low-lying regions (www.eoearth.org)

  12. The Greenhouse Effect: Atmospheric Properties & Climate Change John Tyndall (1820-1893): Measured infrared radiation absorption properties of atmospheric molecules Changing H2O or CO2 could cause “all the mutations of climate which the researches of geologists reveal” (en.wikipedia.org) Svante August Arrhenius (1859 -1927): 40%  or  in CO2 could explain advance & retreat of glaciers. (2xCO2 T ~ 4˚C.) Human CO2emissions could prevent another ice age. Nobel Prize - Chemistry (1903) (en.wikipedia.org)

  13. The Greenhouse Effect: Impact of Humans? Guy Stuart Callendar (1897-1964) 2xCO2 T ~ 2˚C Must treat atmosphere as set of interacting layers, not a single slab. Speculated, with others, that T over first part of 20th Century was anthropogenic. (www.aip.org) Criticisms: Overlap of H2O and CO2 absorption bands  saturation  no impact of increasing CO2. Earth regulates CO2 amounts, esp. via ocean. Humans have negligible impact.

  14. Other Atmospheric Constituents Other Greenhouse Gases: - Methane (CH4) - Nitrous Oxide (N2O) - CFCs Anthropogenic Aerosols (particles): • Scatter sunlight back to space • Cause more, smaller cloud particles (increase albedo) (oea.larc.nasa.gov)

  15. The Climate System How do we simulate this?

  16. Development of Global Climate Models (GCMs)    What is this? Computing demand increases inversely with cube of horizontal resolution. Increased computing power has allowed increased resolution …

  17. Development of Global Climate Models (GCMs) … and increasing complexity. Which should be favored?

  18. Complements to GCMs Global stretched-grid models Regional (limited-area) models

  19. Example Regional Model Domain

  20. Contrast the Hadley Centre GCM … 2.5˚ (lat) x 3.75˚ (lon) (Mt/Ag/EnSc/EnSt 404/504 - Global Change) History (from IPCC WG-I, Chapter 1)

  21. … with a regional model ~ 0.5˚ (lat) x ~ 0.5˚ (lon) (Mt/Ag/EnSc/EnSt 404/504 - Global Change) History (from IPCC WG-I, Chapter 1)

  22. How Well Have GCMs performed? One test: Projected changes in global temperature T [˚C] Much more detail later (AR4, Chapter 8)

  23. END Historical Perspectives onClimate Change Research

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