Are We Getting Warmer?

1. Are We Getting Warmer?

2. Is the Earth getting warmer? • Yes • No

3. Is change in the Earth’s climate mostly caused by natural causes or by humans? • Natural causes • Humans

4. How do you measure a planets temperature? • If you have them, then thermometers spread around the earth can tell us the average temperature. • These record go back to the mid 19th century. • Earlier records not standardized so they have more uncertainty.

5. What affects individual temperature measurements? • Geographic variations • Local microclimates • Land use/heat islands • Technique • Land or sea • All of the above

6. Records must account for sea surface temperature, heat islands around cities, land use changes, measurement techniques. • Thermometers may differ in calibration. • Look for trends in temperature rather than absolute temperatures. • Usually want to determine anomalies rather than absolute values. • Anomalies are deviations from average temperature.

7. Regional Patterns • Warming is greater on land than in oceans (specific heat) • Warming is larger in northern hemisphere (more land and more GHG) • Arctic has warmed at twice the global rate • Ice-albedo feedback, • lower evaporation; more energy directly to the surface

8. Regional Temperature Anomlies

9. Zonal Mean Temperature Anomolies

10. Is the temperature rise unusual? • Before 1850 we have very little direct thermometric data so we use “proxies” for measuring the temperature from long ago. • Examples: tree rings, lake sediments, bleaching of coral reefs, isotope ratios

11. Temperature for 1000 years.

13. Greenland Ice Cores

14. CO2 and Temperature are strongly correlated. • Probably not cause and effect.

15. Correlation • Chronological relationship between two factors • Expressed as a number between -1 and 1 • Does not prove causal relationship • Rising of Sirius  flooding of the Nile • Coming to physics class  falling asleep

16. CO2 and Temperature are strongly correlated. • Probably not cause and effect. • Small chances in temperature are caused by small orbital changes. • Small increase in sea surface temperature causes some CO2 to come out of solution. • Increase in land surface temperature increases microbial action  more CO2 • More CO2 in the air cause further warming.

17. Using Isotope ratios we can go back millions to billions of years to find temperatures. • 16O vs. 18O • 1H vs. 2H • Compare ratios in different layers of ice. • Arctic yields clearer results.

18. Evidence for Rapid Temperature Changes in Greenland Ice Core

19. Younger Dryas • The Big Freeze • Approximately 15,000 years ago; 1300 year duration • Caused by collapse of North American ice sheets(?) • Believed to be nonlinear effects due to changes in ocean circulation when there was a large influx of fresh water from glacial melting

20. Ocean Currents

21. Caution: The rapid fluctuation in the Younger Dryas are Arctic temperatures which exaggerate global climate changes. • Fluctuation not so obvious in proxies from other regions of the world. • The rapid changes that we are experiencing now are global. They are also more exaggerated in the polar regions.

22. Reduction in Sea Ice1979-2005

23. Decline in Sea Ice

24. Not only is there less area of sea ice, it is also thinner.

25. Melting Glaciers

27. Global Warming Indicators • Global temperature • Ice sheets (Greenland, Antarctic) • Arctic sea ice • Glaciers • Ocean surface temperature • Sea level

28. Is the Warming Anthropogenic?

29. Chicago Tribune 31 March 2006