asper, 2007 slide 1 lesson #12 the ocean’s future: global warming vernon asper usm
TRANSCRIPT
Asper, 2007Asper, 2007 Slide Slide 11
Lesson #12The Ocean’s Future: Global warming
Vernon Asper
USM
Asper, 2007Asper, 2007 Slide Slide 22
• Public awareness of global warming is new
• This is what I grew up believing
• This is the current record
• Perspective is critical
http://en.wikipedia.org/wiki/http://en.wikipedia.org/wiki/Image:Instrumental_Temperature_Record.pngImage:Instrumental_Temperature_Record.png
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Global Climate Change• Climate is greatly affected by water masses in
the oceans. The movement of large water masses redistributes heat in the ocean.
• Since the oceans cover 70% of the Earth’s surface, this movement has a major affect on the overlying atmosphere and thus climate.
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Global Climate Change• The Greenhouse Effect:
– sunlight penetrates the atmosphere
– it hits the earth and heats it
– heat given off by the earth is trapped by the atmosphere
– some gases are better than others at trapping this heat
http://www.acmecompany.com/stock_thumbnails/13808.greenhouse_effect_2.jpghttp://www.acmecompany.com/stock_thumbnails/13808.greenhouse_effect_2.jpg
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• CO2 does affect climate!
http://upload.wikimedia.org/wikipedia/en/d/d2/Atmospheric_CO2_with_glaciers_cycles.gifhttp://upload.wikimedia.org/wikipedia/en/d/d2/Atmospheric_CO2_with_glaciers_cycles.gif
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Global Climate Change
• Since we’ve started burning fossil fuels (oil and coal):– the amount of carbon dioxide in the atmosphere has increased
– we can expect temperatures to follow
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Global Climate Change• Yes, temperatures are warming!
• Note the scale http://data.giss.nasa.gov/gistemp/graphs/Fig.A.lrg.gif
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Global Climate Change (Cont.)
• As temperatures rise, ice will melt glaciers from polar regions
• This would cause sea-level to rise.
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• Let’s look back in time• Is this warming new?• Sort of• Note the
cooling
that was
taking
place
for
800 Years!
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The climate record: how we know what we know.
• Ice cores• Sediment cores• Beach profiles• Glacial records
– Scarring, moraines, etc.
– “glacial
erratics”
G. Gaitan VazOperations East Coast II, Marine Wing, Geological Survey of India,41, Kirlampudi Layout, Visakhapatnam 530 017, India
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Ice cores• Greenland and Antarctica
– Record climate records in both hemispheres
– Continuous records back to >400,000 YBP
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Ice core challenges
• Acquisition– Vostok is near the
“south pole of inaccessibility”
– Average temperature
around -50C
• Ice deformation– Compression
– Thinning
– Flow
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Ice core sampling and analysis
• Age– Count layers
• Visual and conductivity which changes seasonally– 14C
• Temperature– Measured directly; insulated well enough to preserve major
features– stable isotopes (next slides)
• CO2, methane, other gases– Air bubbles trapped in snow– Dissolved in water
• Dust from volcanoes– Golden spike to correlate cores– Evidence for large eruptions
Science: Dahl-Jansen et all, 1998
LIA:Little Ice AgeCO: Climateic Optimum
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• So, from historical records, we can look at the recent past……
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• …..and from ice cores, we can go back 100,000’s of years• LOOK! On this scale, the earth has been cooling for 8,000 years!
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• This record from Greenland shows the temperatures since the last ice age
• Lots of variability
• Abrupt warming 12,000 years ago.
http://math.ucr.edu/home/baez/temperature/http://math.ucr.edu/home/baez/temperature/
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• This warming caused the sea level rise that we’ve been discussing all semester– Estuaries = drowned river valleys
– Continental shelves
– Relic sedimentshttp://en.wikipedia.org/wiki/Image:Post-Glacial_Sea_Level.pnghttp://en.wikipedia.org/wiki/Image:Post-Glacial_Sea_Level.png
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• Yes, just 18,000 years ago, there was a LOT of ice around. Most disappeared a very long time ago but some remains
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• Looking back further, we see that the earth has been cooling steadily for more than 5 million years
• But there are odd oscillations
• Natural oscillations
• Of about 2°C
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•Now lets look WAY back into the earth’s history
•Look how warm it was then!!
•And sea level was higher
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• The long term temperature story:– Earth’s
colder now than it’s been for most of the last 150 million years!
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Factors affecting climate•Orbital parameters•Sunspots
– More= warmer
– 11 year cycle
•Volcanic eruptions•Tectonics•Carbon dioxide•Methane•Ocean Circulation
http://en.wikipedia.orghttp://en.wikipedia.org
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• The earth’s orbit isn’t entirely circular– Obliquity
– Precession
– eccentricity
• The tilt changes
• The timing of winter changes
Tilt
Obliquity
Precession
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`
• Dashed blue = sunlight• Red / blue = temperatures• Remarkable correlation• 5,000 year lag
http://www.roperld.com/graphics/LIAInsolation.jpghttp://www.roperld.com/graphics/LIAInsolation.jpg
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Factors affecting climate•Orbital parameters•Sunspots
– More= warmer
– 11 year cycle
•Volcanic eruptions•Tectonics•Carbon dioxide•Methane•Ocean Circulation
http://en.wikipedia.orghttp://en.wikipedia.org
Asper, 2007Asper, 2007 Slide Slide 2626http://upload.wikimedia.org/wikipedia/commons/c/c2/Vostok-ice-core-petit.png
http://en.wikipedia.org/wiki/Image:Vostok-ice-core-petit.pnghttp://en.wikipedia.org/wiki/Image:Vostok-ice-core-petit.png
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• Greenland is usually cold, even when the rest of the earth is warm
• It has been warmer over the last 10,000 years than “normal”
• But note the oscillations!!!
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• The last ice age:
• Temperature and CO2 correlate very well
• Cause and effect?
http://www.clearlight.com/http://www.clearlight.com/~mhieb/WVFossils/~mhieb/WVFossils/last_50k_yrs.htmllast_50k_yrs.html
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Temperature rises first; CO2 follows!
• Warming is FAR more rapid than cooling
• Temperatures warm, then CO2 increases
• Many glitches
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• But CO2 levels are higher now than they’ve been for 400,000 years
• We “expect” more warming
• But we don’t really know
what caused these fluctuations?
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Natural CO2 fluctuations
• Sequestration of carbon– Carbon is converted to organic matter and buried
• Release of carbon– Buried carbon is exposed and oxidized
• Geologic outgassing– Natural release of CO2 by the earth
• Weathering of silicate rocks– Weathering removes CO2 from the atmosphere
– Plate motions cause variations in the amount of rocks exposed to weathering
– This is a VERY slow process!
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Impacts of Warming:
• Warming: ~6°F in next 100 years– Except in Europe where it will be cooler?
• Effects vary regionally: rain, temps • Vulnerable ecosystems: Arctic, alpine• Water supplies?• Food supplies?• Diseases?• Increased forest growth• Damage to coastal infrastructure• Surprises: “significant uncertainties remain?
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• 1979 and 2003• Arctic sea ice coverage
has been reduced• Many predict an ice-
free Arctic Ocean in a few decades
• This will impact commerce and defense
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• Climate belts shift• By the year 2095:
– Illinois will have Arkansas winter weather
– Illinois will have Texas summer weather
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• Melting glaciers and thermal expansion will cause sea level to rise
• this will seriously impact coastal communities
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• But is this statement true?
http://http://www.sciencedaily.com/www.sciencedaily.com/releases/releases/2005/08/050804123855.htm2005/08/050804123855.htm
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•Hardly!
•This is a gross exaggeration
•In truth, the temperature in MOST places in Antarctica is decreasing
•But in others, it’s increasing.
•A lot?
•Not 10°C
•Not even in 50 years
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Recent Ice conditionsRecent Ice conditionsin Antarctica.in Antarctica.Note the huge bergNote the huge berg
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Global Climate Change(Cont.)
• Global warming may also lead to changes in global wind patterns which may cause changes in ocean currents
• This will:– Alter upwelling and downwelling.
– Alter nutrient availability and productivity.
– Affect migration patterns of marine organisms.
• Affect tropical storms?– Increased shear
– Fewer storms?
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Deep-Ocean Circulation• Brings heat to the North Atlantic
• Occurs in North Atlantic because of precise salinity and temperature conditions
• If these change and it shuts down, this area will cool dramatically
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• Remember the “Younger Dryas”?• What caused it?• We think it was the oceans!
http://math.ucr.edu/home/baez/temperature/http://math.ucr.edu/home/baez/temperature/
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Younger Dryas• Dryas: flower from
Europe– Requires cold climate
• Younger: early part of the period
• Greenland warmed by 15ºF in a decade or less
• Winds: less during colder periods?
• A Global event
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Younger Dryas• Lasted 1,300
years• Very cold• Atmosphere:
– 3X more sea salt • (wind over oceans)
– 4-7X more dust • (wind over arid places)
• Most likely cause?– Shut down of conveyor circulation!
• Caused by draining of Lake Agassiz• Lake formed from glacial runoff• Ice dam broke, flooding Arctic with fresh water• Recovery required freezing/removal of fresh wter cap
– Comet?
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Effect of shutting off deep circulation• The north Atlantic would cool• Other areas would warm, especially in the
Southern Hemispherehttp://www.cru.uea.ac.uk/cru/info/thc/http://www.cru.uea.ac.uk/cru/info/thc/
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Summary• Climate is complicated; not easily modeled
• The oceans play a huge role
• Climate has changed in the past, is changing now and will change in the future but we don’t know for sure how it will change
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What should we do?
• This is for YOU to decide:
• 1) Nothing: just let “nature” take its course
• 2) Nothing, but: give up on limiting CO2 emissions but work on dealing with the impacts
• 3) Encourage developed countries to reduce emissions
• 4) Mandate that all nations reduce emissions
• 5) Use “countermeasures”:– dust blanket
– Umbrella in space
– Pump CO2 into the ocean
– Install “Lovelock” nutrient pumps
– ??