Transcript Earth`s Climate System Today

Earth’s Biosphere
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Interaction of physical processes in Earth’s
climate system with biosphere
 Results from the movement of carbon
Carbon Cycle
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Carbon moves freely between reservoirs
 Flux inversely related to reservoir size
Photosynthesis
photosynthesis
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6CO2  6 H 2O
C6 H12O6  6O2
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oxidation
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Sunlight, nutrients, H2O
Transpiration in vascular
plants
 Efficient transfer of
H2O(v) to atmosphere
Oxidation of Corg
 Burning
 Decomposition
Terrestrial Photosynthesis
CO2 and sunlight
plentiful
 H20 and correct
temperature for
specific plants not
always sufficient
 Biomass and biome
distribution
controlled by rainfall
and temperature
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Local Influence on Precipitation
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Orographic precipitation influences distribution
of biomass and biomes
Influences the distribution of precipitation
Marine Photosynthesis
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H2O, CO2 and sunlight
plentiful
Nutrients low (N, P)
Nutrients extracted
from surface water by
phytoplankton
Nutrients returned by
recycling
 Upper ocean (small)
 Upwelling (high)
 External inputs
(rivers, winds)
Ocean Productivity
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Related to supply of
nutrients
Nutrient supply high in
upwelling regions
 Equatorial upwelling
 Coastal upwelling
Southern Ocean
 Wind-driven mixing
 Short growing season
 Light limitation
Productivity – Climate Link
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“Biological Pump” –
photosynthesis
takes up CO2 and
nutrients, plants
eaten by
zooplankton, dead
zooplankton or
excreted matter
sinks carrying
carbon to
sediments
Export – Removal of Carbon
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For every 1000 carbon
atoms taken up by
phytoplankton
50-100 sink below 100 m
10 are exported to
depths below 1 km
 Stored for millennia
1 carbon atom is buried
in deep sea sediments
 Sequestered for eons
HNLC
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Growth in regions limited by micronutrients (Fe)
 High nutrient low chlorophyll (N. Pacific, SO)
Higher production linked with removal of CO2
Effect of Biosphere on Climate
Changes in greenhouse gases (CO2, CH4)
 Slow transfer of CO2 from rock reservoir
 Does not directly involve biosphere
 10-100’s millions of years
 CO2 exchange between shallow and deep
ocean
 10,000-100,000 year
 Rapid exchange between ocean, vegetation
and atmosphere
 Hundreds to few thousand years
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Increases in Greenhouse Gases
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CO2 increase anthropogenic
and seasonal
 Anthropogenic – burning
fossil fuels and
deforestation
 Seasonal – uptake of CO2
in N. hemisphere
terrestrial vegetation
Methane increase
anthropogenic
 Rice patties, cows,
swamps, termites,
biomass burning, fossil
fuels, domestic sewage
Climate Archives
Four major archives of climate records
 Sediments
 Ice
 Corals
 Trees
 Each archive has different time span,
resolution and ease of dating
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Understanding Climate Change
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Understanding present climate and predicting
future climate change requires
 Theory
 Empirical observations
Study of climate change involves construction
(or reconstruction) of time series of climate
data
 How these climate data vary across time
provides a measure (quantitative or
qualitative) of climate change
 Types of climate data include temperature,
precipitation (rainfall), wind, humidity,
evapotranspiration, pressure and solar
Contemporary & Past Climate
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Contemporary climate studies use empirically
observed instrumental data
 Temperature records available from central
England beginning in the 17th century
 Period traditionally associated with
instrumental records extends back to middle
of the 19th century
Climate change from periods prior to the
recording of instrumental data
 Must be reconstructed from indirect or proxy
sources of information
Climate Construction from Instrumental
Data
 Contemporary climate change studied by
constructing records (daily, monthly and
annual) which have been obtained with
standard equipment
 Temperature
 Rainfall
 Humidity
 Wind
Paleoclimate Reconstructions
Climate varies over different time scales
and each periodicity is a manifestation of
separate forcing mechanisms
 Different components of the climate
system change and respond to forcing
factors at different rates
 To understand the role each component
plays in the evolution of climate we must
have a record longer than the time it takes
for the component to undergo significant
change
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Paleoclimatology
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Study of climate change prior to the period of
instrumental measurements
Instrumental records span only a fraction (<10-7)
of Earth's climatic history
 Provide a inadequate perspective on climatic
variation and the evolution of the climate
today and in the future
A longer perspective on climate variability can be
obtained by the study of natural climatedependent phenomena
Such phenomena provide a proxy record of the
climate
Paleoclimate Proxy Records
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Many natural systems are dependent on climate
 It may be possible to derive paleoclimatic
information from them
By definition, such proxy records of climate all
contain a climatic signal
 The signal may be weak and embedded in a
great deal of (climatic) background noise
 Proxy material acts as a filter, transforming
climate conditions in the past into a relatively
permanent record
 Deciphering that record can often be complex
Proxy Data
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Proxy material can differ according to
 Its spatial coverage
 The period to which it pertains
 Its ability to resolve events accurately in time
For example
 Ocean floor sediments, reveal information about long
periods of climatic change and evolution (107 years),
with low-frequency resolution (103 years)
 Tree rings useful only during the last 10,000 years,
but offer high frequency (annual) resolution
The choice of proxy record (as with the choice of
instrumental record) depends on physical mechanism
under review
Factors to Consider
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When using proxy records to reconstruct paleoclimates
one must consider
 The continuity of the record
 The accuracy to which it can be dated
 Ocean sediments may be continuous for over 1
million years but are hard to date
 Ice cores may be easier to date but can miss layers
due to melting and wind erosion
 Glacial deposits are highly episodic, providing
evidence only of discrete events in the past
Different proxy systems have different levels of inertia
with respect to climate
 Some systems vary in phase with climate forcing
 Some systems lag behind by as much as several
centuries
Steps in Reconstructing Climate
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Paleoclimate reconstruction proceeds through a
number of stages
st stage is proxy data collection, followed
 The 1
by initial analysis and measurement
 This results in primary data
 The 2nd stage involves calibration of the data
with modern climate records
 The secondary data provide a record of
past climatic variation
 The 3rd stage is the statistical analysis of this
secondary data
 The paleoclimatic record is statistically
described and interpreted
Proxy Calibration
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The uniformitarian principle is typically
assumed
 Contemporary climatic variations form a
modern analog for paleoclimatic changes
 However the possibility always exists
that paleo-environmental conditions
may not have modern analogs
 The calibration may be only qualitative,
involving subjective assessment, or it
may be highly quantitative
Proxy Calibration: An Example
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Emiliania huxleyi is one
of 5000 or so species of
phytoplankton
Most abundant
coccolithophore on a
global basis, and is
extremely widespread
 Occurs in all except
the polar oceans
Produces unique
compounds
 C37-C39 di-, tri- and
tetraunsaturated
methyl and ethyl
ketones
Alkenones as biomarkers
• Long-chain (C37-C39) di-, tri- and tetraunsaturated methyl and ethyl ketones
(alkenones) found in oceanic sediments
Emiliania huxleyi Blooms
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E. huxleyi can occur in
massive blooms
 100,000 km2
 During blooms E.
huxleyi cell
numbers usually
outnumber those of
all other species
combined
 Frequently they
account for 80
or 90% of the
total number of
phytoplankton
SeaWiFS satellite image of bloom off Newfoundland
in the western Atlantic on 21 July 1999
Emiliania huxleyi Makes
Alkenones
UK’37 Varies with Temperature
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Alkenone unsaturation
global calibration
 UK’37 determined in
core top sediment
samples
 SST from from
Levitus ocean atlas
 Figure from Muller
et al. (1998)
Global UK’37 SST Correlation