Chapter 14 - Title

1. Chapter 14 - Title

2. Contents Proxy Records Long term Temperature Record Feedback Natural Mechanisms Anthropogenic Effects Consequences of a Warmer World

3. Waterworld What would happen to the world's coastlines… if the West Antarctic Ice Sheet melted? if the East Antarctic Ice Sheet were to melt?

4. Some Questions Earth's climate has always been changing produced ice ages Climate variations have been seen in the past what physical processes create natural fluctuations in the earth's climate? Man-made influence on climate change? is so, what will it's effect be? how do we measure climate change in the past? how are we predicting climate change in the future?

5. Proxy Records Sediment and Ice cores. the sediment contains calcium carbonate shells from organisms that have lived near the earth's surface in the past the type of calcium carbonate shell can tell you something about temperature since some live only within narrow temperature ranges.

6. Oxygen Isotopes normal oxygen contains 8 protons, 8 neutrons (16O) a small fraction (one in a thousand) of oxygen atoms contain 8 protons, 10 neutrons (18O) this is an isotope of oxygen and is heavier than 16O 16O will evaporate more readily than 18O since it is lighter Hence, during a warm period, the relative amount of 18Owill increase in the ocean waters since more of the 16O is evaporating Hence, looking at the ratio of 16O to 18O in the past can give clues about global temperatures. Ice cores from glaciers can also give you similar information

7. Dendrochronology one ring per year distance between rings can tell you something about temperature and moisture fluctuations related to climatic variability Other data offering clues about our past climate: lake-bottom sediment and soil deposits pollen in deep ice caves, soil deposits, and sea sediments geologic evidence is ancient coal beds, sand dunes, and fossils documents concerning droughts, floods, and crop yields Knowledge on past climate is still incomplete....., but what do we know from these sources?

8. Long-Term Temperature Record much of earth's history - warmer than todays climate polar regions ice free warm climate was periodically interrupted by periods of glaciation 700 million years ago (mya) 300 mya more recently, the Pleistocene epoch, or simply the Ice Age occurred 2 mya

9. More recently, North American glaciers reached maximum thickness 18,000-22,000 years ago

10. 14,000 y.a.,, glaciers started to retreat as temps rose 11,000 y.a., temps suddenly fell - referred to as Younger-Dryas Younger-Dryas lasted about 1000 years, then avg temps increased, glaciers retreated. 6,000-5,000 y.a., climate was about 1°C warmer than normal

11. The last 1000 Years Notice that for most of the last 1000 years, the climate has been cooler than normal. The period from about 1550 - 1850 is referred to as the Little Ice Age Figure from IPCC Working Group I Report Figure from IPCC Working Group I Report

12. Recent Trends > 1800's, a warming trend avg temp has increased by 1°C 8 hottest years of this century occurred since 1979 record may be contaminated? corrected data suggest trend of +0.3-0.6°C over last 100 years. Is the warming due to man-made causes enhanced GH effect due to increasing CO2 or due to natural fluctuations in climate? This question is still a subject of debate, but has very important consequences....

13. Summary of Global Warming Observations Rate and duration of warming in 20th century is larger than any other time in last 1000 years. The 1990s are likely to have been warmest decade of the millennium in the Northern Hemisphere. 1998 is likely to have been the warmest year. Note:  A few areas of the globe have not warmed in recent decades:  some areas of Southern Hemisphere and parts of Antarctica Total atmospheric water vapor has likely increased several percent per decade over many regions in NH Annual land precipitation has increased in the middle and high latitudes of the Northern Hemisphere. Increased cloud cover by about 2% since the beginning of the 20th century over the Northern Hemisphere. Decreasing snow cover and sea-ice amounts in NH.  No significant trends in Antarctic sea-ice are apparent. Global mean sea-level rise during 20th century has been observed to be 1.0-2.0 mm per year. Increase in heavy and extreme precipitation events in regions where total precipitation has increased. 

14. Movie What’s Up

15. Climate Change and Feedback Mechanisms Feedback mechanism - when physical processes in the earth-atmosphere system further impact the initial change if the impact is such that the initial perturbation is enhanced, then it is called a positive feedback mechanism --> if the impact is such that the initial perturbation is reduced, or weakened, then it is called a negative feedback mechanism. How can the scenario shown to the right --> be modified to produce a negative feedback cycle?????

16. Negative Feedback Mechanism Here is an example of a negative feedback mechanism--> In reality, there are a large number of feedback mechanisms that involve processes and interactions within and between: the atmosphere the cryosphere the biosphere the solid earth it is indeed a complex system and is why understanding climate change is very difficult!! Now, what are some natural climate change processes????

17. Review What methods do scientists use to determine past climates? How does todays temperature compare to the last 1000 years? What is the Younger-Dryas? Explain positive vs. negative feedback

18. Natural Mechanisms Plate Tectonics Milankovitch Theory Aerosols Variation in Sun Spot Activity

19. Natural Mechanisms - Plate Tectonics Theory of Plate Tectonics - Continental Drift Earths outer shell is composed of plates --> they move at a rate of about 3 cm per year affect of more land at higher latitudes: alter ocean currents and therefore heat transport alter global atmospheric circulation more glaciers over land, higher albedo, cooler temps. plate movement also generates more volcanic activity hence, when the plates are on the move, have more volcanic eruptions -> emit more CO2 into atmosphere this would cause global temps to rise. if there is little movement, volcanic activity decreases -> so CO2 concentrations are lower in the atmosphere -> avg temp decreases

20. Natural Mechanisms - Plate Tectonics

22. Natural Mechanisms - Milankovitch Theory - Eccentricity Cycle Climate change due to variations in the earth's orbit - Milankovitch Theory 1) eccentricity cycle - the earth's orbit around the sun is elliptical. the shape of the ellipse (eccentricity) varies from less elliptical to more elliptical back to less elliptical and take about 100,000 years to complete this cycle. currently, we are in an orbit of low eccentricity (near circular). review - when are we closest to the sun? review - when are we furthest away from the sun? Data analysis for the last 800,000 years of deep-ocean sediments show that ice coverage is a maxima every 100,000 years this matches the Eccentricity cycle period

23. Natural Mechanisms - Milankovitch Theory- Precession Cycle Climate change due to variations in the earth's orbit - Milankovitch Theory 2) Precession cycle - The earth is wobbling about it's axis of rotation like a spinning top To make one complete cycle takes about 23,000 years in 11,000 years, the seasons will switch times during year and will be more severe...., why?

24. Natural Mechanisms - Milankovitch Theory- Tilt Cycle Climate change due to variations in the earth's orbit - Milankovitch Theory 2) Tilt Cycle - currently, the axis of rotation for the earth is tilted at 23.5° However, this value changes from a minimum of 22.5° to a maximum of 24.5° and takes 41,000 years to complete one cycle at 22.5° the seasonal variation will be Answer than current? at 24.5° the seasonal variation will be Answer than current? The Milankovitch cycles and plate tectonics are not the only natural factors which can affect global climate......, there are other factors to consider: amount of dust and aerosols in the atmosphere reflectivity of ice sheets concentrations of trace gases amount of clouds Smaller, largerSmaller, larger

25. Natural Mechanisms - Aerosols in the Troposphere aerosols are tiny liquid and solid particles they enter the troposphere by: factory and auto emissions agricultural burning / wild fires ocean - phytoplankton produce dimethylsulphide (DMS) - DMS forms SO2 in atmosphere which in turn produces sulfate aerosols Aerosol concentrations are increasing with time. Tropospheric aerosol effect on climate: reflects incoming solar radiation - cooling affect absorbs LW radiation - warming effect (especially the black sooty aerosols emitted through fossil fuel and biomass burning) The net effect of tropospheric aerosols is thought to be one of cooling.

26. Natural Mechanisms - Aerosols in the Stratosphere Largely injected by volcanic eruptions remember, the stratosphere is a stable layer, so lighter, smaller aerosols will have long residence times aerosols reflect and absorb short wave radiation As a result aerosols produce warming in the stratosphere and cooling in the troposphere Recent significant eruptions: El Chichon - April 1982 Mount Pinatubo - June, 1991

27. Climate Change - Mt. Pinatubo's SO2 Plume... Mt. Pinatubo injected 20 million tons of sulfur dioxide into the stratosphere! The sulfur dioxide was observed around the globe in the equatorial regions What was the effect on global temperatures???

28. Mt. Pinatubo's effect on Global Temperatures average hemispheric temperatures dropped by 0.2-0.5°C for a period of 1-3 years.

29. Review Evidence suggests the earth’s climate was warmer than it is today

30. Natural Mechanisms - Variation in Sun Spot Activity huge magnetic storms that show up as dark (cool) areas on the suns surface when there are more sunspots, the sun is emitting more energy, hence, the amount of energy incident on the earth increases so, one could imagine warmer climate during a sun spot maximum and cooler climate during a minimum. what does a sun spot look like? sun spot period is about 11 years

31. Anth. Effects - CO2 and other Green House Gases CO2 - natural and anthropogenic sources  recent increase due to fossil-fuel combustion and deforestation CH4 - natural and anthropogenic sources about 1/2 of current emissions are anthropogenic (land fills, natural gas, agriculture) N2O- natural and anthropogenic sources nitrogen-based fertilizers Other important Greenhouse Gases: –CFCs –Ozone –and of course, water vapor!

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33. Climate Change - CO2 Feedback mechanisms other trace gases like N2O, CH4, and CFCs are also increasing - these are also greenhouse gases increased temps will enhance evaporation from oceans -> increased water vapor in atmosphere -> enhanced greenhouse effect increased temps will enhance evaporation -> increase amount of low clouds -> increase earth's albedo CO2 will dissolve into the oceans Vegetation will remove CO2 and grow more vigorously

35. The Source of Global Warming Q:  is the observed warming over the last 50-100 years due to natural climate variability, human influence, or both? “…. natural forcing alone is unlikely to explain the recent observed global warming or the observed changes in vertical temperatures structure of the atmosphere.” “In light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.” Figure and quotes from Technical Summary from IPCC Working Group I

37. Summary What techniques have scientists utilized to reconstruct our past climate? What are the significant climatic events over the last 18,000 years? describe the global temperature trend since the industrial revolution what is a the feedback mechanism? What are examples of positive and negative feedback mechanisms for a warming planet? describe some of the natural causes for climate change: plate tectonics the Milankovitch theory eccentricity cycle precession cycle tilt cycle aerosols in the troposphere and stratosphere' sunspot activity explain the theory of nuclear winter describe the current CO2 concentration trend the trend is caused by???? why will the sea level rise if global warming occurs? what are the IPCC committee conclusions on the subject of global warming? why are predictions for global warming so problematic?

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44. References Jones, Philip D., and Wigley, Tom M. L., (1990) "Global Warming Trends." Scientific American, August 1990, pp. 84-91. Mahlman, J. D. (1997) "Uncertainties in Projections of Human-Caused Climate Warming." Science, vol. 278, 21 November 1997, pp. 1416-1417. Schneider, Stephen H. (1989) "The Changing Climate." Scientific American, September 1989, pp. 70-79. Suplee, Curt, (1998) "Unlocking the Climate Puzzle." National Geographic, vol. 193, no. 5, May 1998, pp. 38-71.