Transcript Geological record of climate change

Geological record of climate change
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Geological record of climate is fairly complete for the
past 100,000 years
 the record shows rapid climate change
Forcing factors and their time spans over which they
could influence climate:
Forcing factors
Time span
volcanic eruption
months to years
meteorite impact
days to decades
atmospheric pollution
months to centuries
changes in oceanic circulation
months to millennia
changes in sea and ice extent
years to millennia
continental drift
millions to billions of years
changes in orbit
millennia
changes in the Sun’s energy
years to billions of years
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Three cycles in the changes in solar luminosity
 11-year sunspot cycle
 78-year Gleissbery cycle
 200-year sunspot cycle
Sunspots
 dark areas on the Sun’s surface
 colder than the surrounding area
 4,000 K (about 3,700° C) vs. 5,800 K (about
5,500° C)
 causes cooling on Earth
 Sunspots caused by changes in Sun’s magnetic field
 Sunspots last from days to even months
 number of Sunspots not always the same
Sunspots observed
during a cycle of high
sunspot activity, March
30, 2001
http://www.oneminuteastronomer.com/
2009/09/11/sunspots/
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our
Energy Future, Columbia University Press. Source: SOHO/MDI Consortium
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Variations in Earth’s orbit around the Sun has influence
on Earth’s climate on a scale of tens of thousands to
hundreds of thousands of years
 Obliquity (tilt), Eccentricity, and Precession (wobble)
Obliquity
 greater the tilt, the colder the winters and the hotter
the summer
 affects Northern Hemisphere much more than
Southern Hemisphere because more land mass at
the former
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Eccentricity
 affects distance of Earth to Sun, so alters total solar
radiation received by Earth
 nearer the Earth to the Sun, hotter
Precession
 wobbling which causes the North Hemisphere to face
closer to the Sun brings greater warming effect
http://en.wikipedia.org/wiki/Axial_precession_(astronomy)
The Milankovitch cycles
21.5 to 24.5
current tilt
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy
Future, Columbia University Press. Source: R. Rohde, Global Warming Art
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Variations in Earth’s orbit has much less effect on
observed warming today than anthropogenic effects
 without greenhouse gases, the variations in Earth’s
orbit are actually causing global cooling
 reducing climate forcing 0.035 Wm-2 per decade
 with greenhouse gases, the climate forcing increases
0.2 Wm-2 per decade
Natural vs. anthropogenic forcing
with human activities
without human activities (natural forcing)
Climate record in Greenland ice
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In 1989, two teams, one European and one American,
begin drilling for ice cores in Greenland
In 1993, they obtained two complete drill cores through
the entire ice sheet
 American team drilled down to 3,053 meters
 European team drilled down to 3,029 meters
These ice cores contained the continuous geological
record of climate for the past 110,000 years
The location of Greenland Ice
Sheet drill sites
E.A. Mathez, 2009, Climate Change: The Science of Global
Warming and Our Energy Future, Columbia University Press.
Source: Geological Survey of Greenland
Greenland ice core
E.A. Mathez, 2009, Climate Change: The Science of Global Warming
and Our Energy Future, Columbia University Press. Source: NOAA
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Ice forms as the snow laid down each year compacts
and recrystallizes into ice during their burial by younger
layers of snow
Newly fallen snow is porous and mixed with air
As the snow recrystallizes, some of the air is trapped to
form bubbles in the ice
 dust also accumulates, so the ice holds samples of
ancient atmosphere and its dust
Greenland is the best place to obtain ice cores because
of higher accumulation of snowfall in Greenland
 20 cm a year at Greenland
 2 cm a year at Antarctica
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Annual layers in ice is determined by
 variations in cloudiness which is caused by the
differences in bubble and ice grain size
 radiocarbon dating of entrapped CO2
Calibration of age by comparing the date of a known
event
 such as high sulfuric acid content in a layer of the ice
core with a known volcanic eruption date
Annual layers of the Greenland ice core (1837 m depth)
http://en.wikipedia.org/wiki/Dye_3
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The site at Greenland was chosen for ice core drilling
because
 close to ice drainage divide (where ice flows in
opposite directions)
 less mixing of annual layers
 bedrock is relatively flat
 important because when ice flows, it folds and
fractures, disrupting/mixing the annual layers
Ice cores
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18O
(heavy isotope) and 16O (light isotope)
 18O is 0.2% of O2, the rest (99.8%) is 16O
When liquid water evaporates to vapour or when vapour
condenses to liquid water,
 18O is enriched in the liquid and 16O is enriched in the
vapour
As water-laden air flows northward and cools, it loses
more and more of vapour as precipitation, so
increasingly more 16O but increasingly less 18O in the air
In cool periods, ice formed in Greenland has more 16O
than the ice formed during warm periods
 air that provides the snow to Greenland loses more of
its water before it reaches Greenland during cold
periods than during warm periods
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The concentration of Ca, Na, and Cl are also indicators
of past climate
Ca is present mainly as carbonate and represents
atmospheric dust
In cool periods,
 the air circulation system scours dust from a wider
land area, so more dust present in the air
 air is drier, leading to more drier (arid) regions and
more dust to be scoured by air
Na and Cl are from the ocean as sea salt
Both dust and sea salt reach Greenland in the late winter
to early spring
The record of temperature in the Greenland ice cores
Today
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our
Energy Future, Columbia University Press. Data from Mayewski et al., 1997
The record of the
Younger Dryas in the
Greenland ice cores
Years before present
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our
Energy Future, Columbia University Press. Data from Mayewski and Bender, 1995
Santorini (?), Greece
approx. 1627 B.C.
The record of major volcanic eruptions in the Greenland ice cores
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our
Energy Future, Columbia University Press. Data from Zielinski et al., 1994
Ocean sediments
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Every year, 6-11 billion tons of sediment accumulate on
the ocean floor
 sediment consists of dead planktonic (near surface
dwelling) and benthic (deep-water dwelling)
The marine sediment record is rather complete but
burrowing organisms and ocean currents commonly
disturb/mix the layers
NOAA Image Gallery
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Climate conditions can be deduced from the
composition, abundance, and characteristics of the
fossils in the sediment
 18O:16O ratio in the hard shells of sea-dwelling
creatures
 high ratio means high evaporation rates (leaving
18O behind in the sea), thus, indicating warm
period
 higher dust (from winds) content indicate cool periods
 cool periods indicated by low humidity and
stronger winds which scours more dust
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Foraminifera, or forams, (protozoa) and diatoms (algae)
are commonly used as microbial climate proxies
They are both planktonic (near surface-dwelling) or
benthic (bottom- dwelling) creatures
Foram shells are made up of calcium carbonate (CaCO3)
while diatom shells are composed of silicon dioxide
(SiO2)
 Their shell remains are taken from sediments and
analyzed
 warmer water tends to evaporate off more of the
lighter isotopes (16O), so shells grown in warmer
waters will be enriched in the heavier isotope (18O)
Diatoms
http://starcentral.mbl.edu/microscope
Forams
http://starcentral.mbl.edu/microscope/
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The abundance of certain microorganisms is an indicator
of sea surface temperature
 determine the foram and diatom population dynamics
Relative abundance and species composition may
indicate environmental conditions
Warmer weather will usually cause organisms to
proliferate (population explosion)
Each species has a particular set of ideal growing
conditions, so species composition (or combination) at a
particular site at a particular time may indicate past
environmental conditions
Lake sediments
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Sediments in mid-latitudes lake
 high carbonate contents correlate with extensive
global ice volumes, reflecting low quantities of water
entering the lake and more brackish (salty) lake water
 low carbonate correlate with warm periods, when
water level of lakes was high and the water fresher
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Varves
 alternating light and dark layers in sediment in lake
valleys
 In winter, lake surface is frozen, so no sediments
enter water and microscopic organisms die from lack
of light for photosynthesis. Fine clay still suspended in
the lake will settle and accumulate at the lake bottom,
producing a dark layer
 In spring, sediments and nutrients (from runoff) enters
the lake. The sediment settle and accumulate at the
lake bottom as a light layer
Thickness of dark layers reflect summer biological
activity/productivity
Thickness of light layers reflect the amount of meltwater
entering the lake
Varves exposed on the campus of the University of
Massachusetts, Amherst
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future,
Columbia University Press. Photograph by J. Beckett, American Museum of Natural History
Corals
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Corals can be used to determine short term climate
changes
Corals build skeletons by extracting Ca and carbonate
from sea water
Corals formed during winter and summer have different
densities
Ratio of 18O:16O reflect seawater temperature
Concentration of trace elements (such as Cd and Ba)
can be analyzed to determine
 upwelling and changes in windblown sediment or river
runoff entering the ocean
 high Cd and Ba indicate increased upwelling of
water
Coral
E.A. Mathez, 2009, Climate Change: The Science of Global Warming
and Our Energy Future, Columbia University Press. Photograph by
D. Finnin, American Museum of Natural History
Dendroclimatology
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Each year, trees add a layer of growth between the older
wood and the bark. This layer, or ring as seen in cross
section, can be
 wide = indicating a wet season (good growth)
 narrow = indicating a dry growing season (poor
growth)
Tree rings indicate good or bad growing seasons which
reflect available moisture, temperature, and cloud cover
Limitations
 past climate record not as long as ice cores
 time span obtained so far is 11,000 years of
climate record
 tree growth is sensitive to local growing conditions
 may not represent global climate at that time
Cross section of a tree trunk being prepared
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future,
Columbia University Press. Photograph by R. Mickens, American Museum of Natural History
http://www.priweb.org/globalchange/clima
techange/studyingcc/scc_01.html
http://www.beringia.com/climate/content/treerings.shtml
Stomata
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Plant fossils from buried sediments are a relatively new
tool being used to unravel Earth's carbon dioxide (CO2)
history
Stomata are tiny pores on plant leaves which regulate
carbon dioxide absorption and water vapor release
 for photosynthesis (inhale CO2, exhale O2)
Lesser number of stomata indicative of high atmospheric
CO2, and greater when atmospheric CO2 is low
http://evolution.berkeley.edu/evolibrary/article/0_0_0/mcelwain_03
An illustration of the stomatal CO2 proxy. (Left) Photomicrograph of fossil leaf
cuticle of the fern. (Right) The fern's nearest living relative, Stenochlaena palustris
The stomatal index of the fossil cuticle is considerably lower than the extant
cuticle, indicating that CO2 was higher directly after the K/T boundary than today.
Photos courtesy of Barry Lomax (University of Sheffield, Sheffield, U.K.)
(Scale bars, 10 μm)
Royer D L PNAS 2008;105:407-408
Stomatal Index, SI (%) = 100 x NS / (NS + EC)
where NS is the number of stomata and EC is the number of epidermal cells
Ph.D. dissertation of Tom van Hoof: "Coupling between atmospheric CO2 and temperature during the onset of the Little
Ice Age“; http://igitur-archive.library.uu.nl/dissertations/2004-1214-121238/index.htm
Climate change : the science, impacts and solutions. 2nd edn. A. Barrie Pittock, CSIRO, Australia, 2009
Past climate
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Using proxy data, Mann et al. (1998) reconstructed the
climate for the past 1000 years
 known as the famous “hockey stick” graph
Mann ME, Bradley RS, Hughes MK (1998) Global-scale temperature patterns and
climate forcing over the past six centuries. Nature 392:779–787.
http://www.guardian.co.uk/environment/2010/feb/02/hockey-stick-graph-climate-change
Instrumental Temperature Record
http://en.wikipedia.org/wiki/Temperature_record_of_the_past_1000_years
Richter, B. 2010. Beyond Smoke and Mirrors: Climate Change and Energy in the 21st Century. Cambridge University Press, New York
http://motls.blogspot.com/2006/07/carbon-dioxide-and-temperatures-ice.html
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The Antarctic temperature starts to change first, followed
by CO2
 responds between 800- and 1000-year lag
Why CO2 lags temperature?
 Oceans are large, and it simply takes centuries for
them to warm up or cool down before they release or
absorb gases
 warm oceans hold CO2 lesser than cold oceans
 so warming ocean releases CO2 slowly and
gradually
 this is why even if no more antropogenic CO2 is
released today, the Earth will still warm because of
“past CO2” being gradually released by the oceans
Climate tipping points
World Development Report 2010: Development and Climate Change, The World Bank, Washington, 2010