Transcript met60-topic02

MET 60
Chapter 2:
The “big picture”
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• Read Chapter 2 ASAP.
• The atmosphere is just one “sphere” on Earth.
• There are several others.
• They all interact!
• Ultimately to understand climate, we need to understand all
systems and interactions.
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The systems…
• The atmosphere.
• The oceans (part of the hydrosphere):
– Structure (thermal)
– Content (salt)
– Motions
• The cryosphere – ice:
– Polar regions
– Greenland & Antarctica
– Permafrost regions
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• The biosphere – everything living (DNA-based):
– Oceanic
– Land-based
• The “solid” earth:
– Plate tectonics & paleoclimate
– Volcanic gases
– Carbon locked in (“sequestered” e.g., in rocks)
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Various “cycles” are important for weather and climate,
including:
• The water cycle (2.2)
• The carbon cycle (2.3)
• Oxygen (2.4)
Finally section 2.5 gives an overview of Earth’s climate history
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The Oceans (part of the hydrosphere)
• Cover 72% of planet – hence VIP
• Enough water to cover planet with a layer 2.6 km deep
• Salty!
• On average 35 g of salts per kg of fresh water
• Salt water is denser than fresh water
– this matters because…see below…
• Remember that fresh water is densest at 4C
(hence – ice floats)
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Vertical density structure…
• Fig 2.2
• Maximum density gradient layer is called the thermocline
(or pycnocline)
– A density equivalent to an inversion
– Inhibits vertical mixing (between upper and lower ocean)
• Top layer of ocean is a mixed layer
– Rain → salinity/density decrease
– Evaporation → salinity/density increase
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Water masses…
• We talk of water masses, which retain their properties of
temperature and salinity as they move.
– A bit like air masses!
• Use this idea to trace motions etc. in the oceans
For the Atlantic…
• Antarctic Bottom Water (AABW)
– Very cold and dense (salty)
– Formed as ice forms at the Antarctic and salt is expelled,
leaving the surface water cold and dense
– Eventually sinks → AABW
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• North Atlantic Deep Water (NADW)
– Also cold and dense – not quite as dense as AABW
– Formed as ice forms around the Arctic
• Mediterranean Outflow
– Warm and very salty
Fig 2.8 shows the arrangement of these masses:
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AABW @ bottom (sinks down…)
NADW above (sinks down…)
“intermediate” water above
Surface water above (wind-driven flows)
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Thermohaline circulation…Fig. 2.7
• http://en.wikipedia.org/wiki/Thermohaline_circulation
• Circulation involving:
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sinking at high latitudes
poleward drift at depth
rising somewhere else
return flow @ surface
• Time involved?
– Hundreds of years!
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Wind-driven surface circulation…Fig 2.4
• Notice prevailing eastward flows in mid-latitude westerly
regions
• Notice ocean gyres
Sea-surface temperatures…Fig 2.11
• SSTs
• Pattern largely controlled by (net) radiative heating
• At lower latitudes, surface circulations → warmer in
western oceans, colder in eastern oceans
• At higher latitudes, opposite (wind driven)
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Sea-surface temperatures…
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Upwelling is an important factor
Due to the wind turning with depth (Ekman effect)
Gives us in N. Cal. our cool water
Cloud decks offshore also → cooling (Fig 1.7)
http://www.ssec.wisc.edu/data/sst/latest_sst.gif
• Often interested in SST anomalies, such as associated with
El Nino
• http://www.noaanews.noaa.gov/stories2009/20090709_elnin
o.html
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The Cryosphere
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Components – Table 2.1 & Fig. 2.12
– be aware of each one and its size (mass, area)
What does the cryosphere do?
1.
Provides thermal inertia to the climate system
– Components warm/cool more slowly
2. Contributes to the albedo
3. Influences (partially drives) the thermohaline oceanic
circulation
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4.
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Freezing @ ice edges
Impacts sea levels via storage
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Over land, ice flows towards edges of ice cap
– e.g., off Greenland – Fig. 2.13
– Greenland ice cap thickness → ice 100,000 years old @
bottom
– Antarctic - 500,000 years old
– Cores → information on past climate (see later)
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Alpine glaciers
– Smaller
– Move faster
– Shrinking rapidly!
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Sea Ice
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Only 1-3 m thick
Once ice starts to form, the ocean is insulated (very cold
above), so additional ice forms more slowly
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Not a solid layer!
Floes and leads! Fig. 2.15
Heat exchange through the leads → complicated picture
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Permafrost
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Global Climate Change effects are enhanced at high
latitudes
Hence – lots of interest now in permafrost
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Fig. 2.17 – understand the curves!
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The Biosphere
Marine biosphere…
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Top layer of ocean = euphotic zone
= where light can penetrate
= photosynthesis
…provided nutrients are provided…
E.g., via upwelling
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Fig. 2.10 → active zones and biological deserts
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Note the impact of El Nino!
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Terrestrial biosphere…
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A biome is an area with a given climate that can support a
give combination of animal and plant life
Fig. 2.19
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Distribution depends on:
Latitude (→ insolation)
Annual average temperature (e.g., > or < 0C)
Annual range of temperature (summer – winter)
Diurnal range of temperature (day – night)
Precipitation amount and distribution
Cloudiness amount and distribution (_______________)
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How does the terrestrial biosphere impact climate (and
weather?)
1.
Impact on hydrological cycle
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Example: on hot days, plants transpire via
evaporating water from leaves
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Cooling of plants
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Reduced heating of the soil as a result
2.
Impact on albedo
3.
Impact on surface roughness
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The solid earth
Make sure you know about plate tectonics and continental drift
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Both play a role in climate
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Plate tectonics → carbon sequestration
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Continental drift → role in climate
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Fig. 2.20
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The hydrological cycle
Spend time looking at Table 2.2
Huge amount in the mantle
Expelled via volcanic eruptions
Large amount in oceans
Considerable amount in ice sheets (Greenland, Antarctica)
Teeny amount in atmosphere!
short residence time!
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Two things of interest:
1.
Precipitation (P) – Fig. 1.25
2.
Evaporation (E)
On the average globally:
EP
Where the overbar denotes an average (always!)
Not true at every location/time!
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Over the Sahara,
E>P
Along the ITCZ,
P>E
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In a column of air somewhere:
P
E
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And…
Tr
P
Tr
Tr
E
Tr is the water vapor flux or transport into/out of the column
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Note that for land…
E
P
atmosphere
soil/rock
T
Where now T is transport into rivers, lakes, aquifers
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The carbon cycle
Imagine following a carbon atom through the carbon cycle:
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Atmosphere:
CO2 and CH4
Terrestrial biosphere:
locked in plants via photosynthesis
CO2 + H2O  CH2O + O2
 carbodydrate
Oceans:
dissolved CO2 in sea water (→carbonic acid, H2CO3)
absorbed into ocean biota
precipitated onto ocean floor (in dead stuff)
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Oceans…
precipitated onto ocean floor (in dead stuff)
Solid earth:
sedimentary rocks (from previous line!)
in/into the mantle via subduction of plates
released back into atmosphere in volcanic eruptions
weathered from the surface soils and rocks
fossil fuels 
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The carbon cycle
Some processes go very fast (photosynthesis)
Some go very slow (subduction etc.)
See Table 2.3 & Fig. 2.23
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Atmospheric carbon
Most in CO2 (also a greenhouse gas)
Well mixed (away from leaves)
Amounts increasing (Fig. 1.3)
Some in CH4 (also a greenhouse gas)
Emitted from rice farming & livestock
Emitted from natural gas (CH4) production
Amounts increasing (Fig. xxx)
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Biospheric carbon
Terrestrial part…Photosynthesis…
Plants take in sunlight (visible) + CO2 + H2O → “food” and O2
Upon decay, plants release CO2 and heat
Fig. 2.24 shows where this is effective (surprising!)
p.43: “if a large quantity of CO2 were injected into the
atmosphere instantaneously…” – the biosphere could not
quickly absorb it
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Oceanic part…Photosynthesis…
Marine biosphere absorbs carbon in euphotic zone
Transports it downward as animals and plants die and sink
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Oceanic (non-biosphere) carbon
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2)
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Dissolved CO2 (carbonic acid, H2CO3)
Carbonate ions (CO32-)
Bicarbonate ions (HCO3-) – largest reservoir
Bicarbonate is incorporated into shells etc.
Carbon in the crust
“Currently, the burning of fossil fuels is returning as much
carbon to the atmosphere in a single year as weathering
would return in hundreds of thousands of years.” – p.45
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Oxygen
Read the main text - basically on the accumulation of O2 in the
atmosphere over time
Oxygen (and other) isotopes
What are they?
Why do we care?
Because isotope data are proxies for climate data:
temperature and other quantities
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Isotopes
a)
The Springfield baseball team (!)
http://en.wikipedia.org/wiki/Springfield_(The_Simpsons)
b)
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atomic things (see (a))
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Isotopes
http://ie.lbl.gov/education/info.htm
http://www.google.com/imgres?imgurl=http://www.emporia.edu/eart
hsci/student/tinsley1/isotopes.gif&imgrefurl=http://www.empor
ia.edu/earthsci/student/tinsley1/webpage1.html&h=142&w=350
&sz=408&tbnid=DBhGIF367Fj6mM:&tbnh=49&tbnw=120&p
rev=/images%3Fq%3Disotopes%2Bof%2Boxygen&hl=en&usg
=__7ylrVMpAzqQUpx2uYXb-7hKLv20=&ei=N7vSpGuGYXwsgOm0e24Cw&sa=X&oi=image_result&resnum=
7&ct=image
http://www.nature.com/news/2009/090909/full/news.2009.901.html
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Example: Oxygen-18 (18O)
In cores of ocean sediments, 18O amounts are enhanced in
times when surface ocean waters are cooler
Thus we examine the ratio 18O/ 16O over time (carbon dating
→ time)
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18O
also changes in response to continental ice sheet volume.
16O
preferentially evaporates (from the ocean)
- leaving more 18O in the ocean
If ice sheets grow (from snow enriched in 16O)
then the ocean & sediments are enriched in 18O
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Example: Carbon-13 (13C)
Low amounts of 13C in organic deposits indicate high levels of
CO2 at the time of plant growth
Thus we examine the ratio 18O/ 16O over time (carbon dating
→ time)
18O
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also changes in response to continental ice sheet volume
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No class Tuesday
Furlough (all faculty)
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Climate History
Much is reconstructed from
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isotope data
geology
modeling!
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Something to remember:
faint young sun
luminosity has increased  30% since planet formed
so???
we should be getting hotter!!!
but…
planet was NOT frozen most of the time
“snowball earth”??
resolution?
atmospheric greenhouse effect
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Past 100 million years…
timeline at
http://www.seafriends.org.nz/books/geotime.htm
Warmer before/cooler after “K-T boundary”
iridium
Glaciation began afterwards
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Past 1 million years…
Glacial and interglacial epochs
we are in an interglacial 
Isotope data reveals links between temperatures and CO2 and
CH4 levels (Fig. 2.31)
LGM = “last glacial maximum” – about 20,000 ya - colder
much lower sea levels (125m)
much lower CO2 concentrations (180 ppmv)
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Variations strongly linked to orbital variations
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Obliquity (tilt…currently 23 ½ )
Eccentricity (small)
Precession
Fig. 2.34
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Past 20,000 years…
Interglacial
Younger-Dryas (cold) event
– see also paper in Asst 3
– see Fig. 2.35
Little Ice Age - 14th – 19th centuries
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