What evidence supports the hypothesis that carbon dioxide is linked to average global temperature? 2 main lines of evidence: Direct measurements Indirect (proxy) measurements –Dendrochronology (study of tree growth) –Isotopic composition of ice, corals, stalactites

Direct Measure Thermometers and other devices that directly measure temperature –Provide a record back to the 1880s when thermometers became common. –Used to calibrate information from other indirect (proxy) sources so that we know we are measuring things by the same metric.

Tree Rings- Dendrochronology Trees develop annual rings in a predictable pattern based on temperature, precipitation, soil conditions, and CO2 availability in their habitat. In areas of the world where we have good records of some of these factors, tree ring data can accurately fill in the blanks on past conditions up to several hundred years ago.

Ice Cores

Ice core samples from Greenland and Antarctica show consistent banding of winter and summer ice formations over hundreds of thousands of years Atmospheric gases, including greenhouse gasses, are trapped in these bands and are easily measurable.

Remember from chapter 6 that isotopes are atoms that share the same number of protons but have different numbers of neutrons in the nucleus. The ratio of oxygen isotopes O16 and O18 varies with global temperature, making temperature measurable in the seasonal bands from ice cores.

Future Predictions

Go to: 1.Watch the 4 animations, record what you see. You will turn these papers in. 2.When you are finished, go to Images and Videos -> Images of Change and browse as a group. 3.I’ll call you back to your seats to discuss what you’ve seen before you leave today.