1. Climate and Climate Change 17 January 2011

2. How and Why Does Climate Change? Climate changes over a broad range of time scales – Years, decades, centuries, millennia Many factors combine to affect climate – Variability of incoming solar radiation – Regular changes in Earth’s orbit – Volcanic eruptions – Changes in Earth’s surface characteristics – Human activities

3. Climate Definition Weather of a locality averaged over a time period – 30 year periods, beginning with start of a decade – Current period is 1971-2000 Plus extremes in weather – Temperature, precipitation, air pressure – Wind speed, cloudiness (may use entire station record) http://www.ncdc.noaa.gov/oa/ncdc.html

4. Climatic Anomalies Departure from long-term climatic average of the average for a particular week, month, or year Precipitation anomalies are more complex than temperature anomalies – Variability of storm tracks – Almost random distribution of convective showers Mid- and high latitudes affected by westerly wave patterns

5. Temperature Anomalies – US, Dec 2007

6. Precipitation Anomalies – US, Dec 2007

7. Climate Boundary Conditions Climate determine by conservation of energy and conservation of mass Climates of specific localities shaped by boundary conditions, e.g., – Latitude, elevation, topography – Proximity to large bodies of water – Earth’s surface characteristics – Atmospheric and oceanic circulation Boundary conditions of first 4 change over 10 6 -10 8 years

8. January Mean Sea-level Air Temperature (  C) Fig. 15.3, p. 455

9. July Mean Sea-level Air Temperature (  C) Fig. 15.4, p. 456

10. Mean Annual Precipitation (mm) Fig. 15.5, p. 458

11. Köppen Climate Classifications Letters h, k and a, b, c, d indicate relative warmth, coolness See Appendix III, p. 509-515 Table, p. 510

12. Earth’s Climate Record Based on Historical documents Fossil plants and animals Pollen profiles Tree growth rings Glacial ice cores Deep sea sediment cores

13. Geologic Time Scale Plate tectonics complicates climate reconstruction Fig. 15.6, p. 460

14. Geologic Time Scale Earliest fossil record of life

15. Plate Tectonics Fig. 15.8, p. 462

16. Geologic Record Fig. 15.10, p. 463 A.Glacial ice volume from deep-sea sediment oxygen isotope analysis B.Temperature variation from ice core oxygen isotope analysis

17. The Last Glacial Maximum Fig. 15.9, p. 463 Occurred 20-18 thousand years ago

18. Glacial/Interglacial Climatic Episodes Fig. 15.11, p. 464 Younger Dryas

19. Lessons of the Climate Past Climate is inherently variable over a large range of time scales (years, decades, centuries, millennia) Variations in climate are geographically non- uniform in both sign (direction) and magnitude Climate change may consist of a long-term trend in various climate elements and/or a change in the frequency of extreme weather events

20. Lessons of the Climate Past (cont’d) Climate change tends to be abrupt rather than gradual (change is faster than duration) Only a few cyclical variations can be discerned from the long-term climate record  Regular cycles: diurnal and seasonal variations, incoming solar radiation  Quasi-regular variations: El Niño, Holocene millennial-scale fluctuations, major glacial- interglacial shifts Climate change impacts society