Contents. Proxy RecordsLong term Temperature RecordFeedbackNatural MechanismsAnthropogenic EffectsConsequences of a Warmer World. Waterworld. What would happen to the world's coastlines
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1. Chapter 14 - Title
2. Contents Proxy Records
Long term Temperature Record
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)
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 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
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
natural and anthropogenic sources
about 1/2 of current emissions are anthropogenic (land fills, natural gas, agriculture)
natural and anthropogenic sources
Other important Greenhouse Gases:
–and of course, water vapor!
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:
the Milankovitch theory
aerosols in the troposphere and stratosphere'
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?
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.