1. Global Climate Change History

2. History of Earth’s Climate Earth formed ~4.6 billion years ago Originally very hot Sun’s energy output only 70% of present Liquid water present ~4.3 billion years

3. History of Earth’s Climate Life appeared ~3.8 billion years ago Photosynthesis began 3.5-2.5 billion years ago –Produced oxygen and removed carbon dioxide and methane (greenhouse gases) –Earth went through periods of cooling (“Snowball Earth”) and warming Earth began cycles of glacial and interglacial periods ~3 million years ago

4. 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)

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

6. The Greenhouse Effect: Impact of Humans? Guy Stuart Callendar (1897-1964) 2xCO 2   T ~ 2˚C Must treat atmosphere as set of interacting layers, not a single slab. Speculated, with others, that  T over first part of 20 th Century was anthropogenic. (www.aip.org) Criticisms: 1.Overlap of H 2 O and CO 2 absorption bands  saturation  no impact of increasing CO 2. 2.Earth regulates CO 2 amounts, esp. via ocean. Humans have negligible impact.

7. The Greenhouse Effect: Impact of Humans By the late 1980s, well-informed people understood that the climate change issue could not be handled in either of the two easiest ways. Scientists were not going to prove that there was nothing to worry about. Nor were they about to prove exactly how climate would change, and tell what should be done about it.” [160] Spencer Weart, The Discovery of Global Warming (2003) http:www.aip.org/history/climate

8. The Greenhouse Effect: Impact of Humans “When the [IPCC] announced in 2001 that they found it “likely” that the current unprecedented rate of warming was largely due to the rise of greenhouse gases, they explained in a footnote what ‘likely” meant: they judged the probability that the finding was true lay between 66 and 90 percent.” Spencer Weart, The Discovery of Global Warming (2003) http:www.aip.org/history/climate