1. CLIMATE CHANGE Global Temperatures: Past, Present, and Future

2. Mean Temperature Mean Temperature of the Earth’s surface is 15 degrees Celsius Locations with the same mean annual temperature can have very different climates, however. –Eg. Beijing and San Francisco, both have a mean annual T of 50 degrees F and 15 inches of rain per year, but climates are very different: –Beijung has large T range, most rain falls in Summer; San Francisoc, very small temperature range and most rain falls in Winter

3. CLIMATE BASICS The Earth receives radiation from the Sun, which is called irradiance The average irradiance, also known as the Solar Constant = 1367 wm -2 The amount varies with: –Latitude –Time of Year –Time of Day –Sunspot Activity –Orbital Variations

4. CLIMATE CHANGE Earth History has seen numerous Ice ages and Warm periods

5. CO 2 Concentration and Global Temperatures for last 160,000 years From: air bubbles in ice cores

6. Last 130,000 years Oxygen isotopes from ice cores in Greenland (Camp Century) and Antarctica (Byrd) can be used to determine sea surface temperatures for the last 160,000 years. A decrease of 1ppm in  O 18 equals a 1.50C reduction in Temp. Warming starts 18-15 ka Cooling starts 60ka

7. Climate Monitors Levels of naturally occurring methane and carbon dioxide both increase with increasing temperatures Notice the high values at about 120ka

8. Evidence for Past Climates Notice in c the period of sudden cooling about 10ka that lasted about 700 years About 1000 AD, climate was warm and Dry: the Medieval Warm Period About 1300 to 1800 AD a cooling trend resulted in the Little Ice Age

9. CLIMATE CHANGE CONTROLLED BY: –Long-term: Plate Tectonics:10 7 -10 8 yr –Placement and sizes of continents –Convection rates (generate more volcanic activity) Solar output increased 30% in last 3 billion years Medium-term: –Orbital Changes:10 4 -10 5 yr --Volcanic Eruptions:long-term increase releases more CO2 and increases temps –Short-term: – Increases in explosive volcanic eruptions increase particulates in atmosphere resulting in cooling 10 0.5 -10 1 yr –Changes in Solar output of 0.1 to 0.2% 22-yr cycle –Fossil Fuel emissions:10 1 to 10 2 yr

10. During the last 2.3 billion years, there have been 7 major Ice Ages with many more minor variations. Most were controlled by the positions of the continents and by the intensity of volcanic eruptions

11. Plate Tectonics affects the positions and sizes of continents TODAY 300 m.y. ago

12. Volcanic Eruptions

13. AXIAL TILT At present, we are near maximum tilt, which makes polar regions have more contrast. Not especially likely to promote cooling.

14. Eccentricity We are near minimum eccentricity, so seasonal contrasts are minimized. Minimum seasonal contrasts promote cooling. Periodicity of 100,000 years

15. Precession Changes in precession occur on a time scale of ~23,000 years. Presently, earth is near maximum tilt of 23.5 0 (range is 21.5-24.5) So maximizes seasonal contrasts Preceesion effect: presently earth is closest to sun in January, farthest in July

16. Milankovitch Cycles Combined result is a difference of +/- 6 0 C

17. The combined Milankovitch curves form an asymmetric curve. Notice how temperature increases are gradual, but cooling can be very rapid.

18. Triggering Mechanisms and Feedback Massive, explosive volcanic eruptions: can introduce huge amounts of ash into the atmosphere. This blocks out some of the sun, increases cloudiness as water vapor nucleates around the particles, and increases precipitation and possible snowfall. Albedo: snow and ice on ground reflect sunlight much more than vegetation or bare rock. This cools the earth’s surface and favors more ice and snow accumulation.

19. CO 2 Budget

20. Temperature Change in Last 150 years

21. CO 2 in Atmosphere for last 50 Years

22. Climate Models predict increases of 4 degrees over the next 100 years. The prediction depends on assumptions about the fossil fuel consumption rate. A: business as usual Means current rate of INCREASE of use of Fossil fuels continues D: CO2 emissions decreased drastically thru conservation, technology, and alternative sources B,C partial changes using other models

23. Sealevel is rising at 2 mm/yr at present

25. CONSEQUENCES OF GLOBAL WARMING CO 2 has increased 50 ppm in the last 40 years to reach 365 ppm. If CO 2 doubles in the atmosphere, much of the earth will become hotter, with larger increases with increasing Latitude. Some climate models say increased evaporation will result in drier climates, while others say increased T will result in increased precipitation.