impactul schimbărilor climatice asupra geochimiei mediului 2
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ImpactulImpactul schimbrilor climaticeschimbrilor climatice
asupra geochimiei mediuluiasupra geochimiei mediului
Universitatea Al. I. Cuza
Facultatea de geografie-geologieSemestrul 7 (2010-2011)
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The topic of global climate changeThe topic of global climate changeillustrates both the scientificillustrates both the scientific
complexities and uncertainties, andcomplexities and uncertainties, and
the difficulties that people andthe difficulties that people and
nations have in formulating rationalnations have in formulating rational
policies addressing the many ofpolicies addressing the many offacets of a changing climate onfacets of a changing climate on
Earth.Earth.
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This course is, among manyThis course is, among manyother things, aboutother things, about
uncertainty, either ordinaryuncertainty, either ordinary
or scientific:or scientific:
Uncertainty is always with us and can neverUncertainty is always with us and can never be fullybe fully
eliminated from our lives, either individually oreliminated from our lives, either individually or
collectively as a society. Ourcollectively as a society. Our understanding of theunderstanding of the
past and our anticipation of the future will always bepast and our anticipation of the future will always be
obscured by uncertainty.obscured by uncertainty.
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Because uncertainty never disappears, decisionsBecause uncertainty never disappears, decisions
about the future, big and small, must always be madeabout the future, big and small, must always be made
in the absence of certainty. Waiting until uncertaintyin the absence of certainty. Waiting until uncertainty
is eliminated before making decisions is an implicitis eliminated before making decisions is an implicit
endorsement of theendorsement of thestatus quo,status quo, andand often an excuseoften an excuse
for maintaining it.for maintaining it.
Predicting the longPredicting the long--term future is a perilousterm future is a perilous
business, and seldom the predictions fall very closebusiness, and seldom the predictions fall very close
to reality.to reality.
Uncertainty, far from being a barrier to progress, isUncertainty, far from being a barrier to progress, is
actually a strong stimulus for, and an importantactually a strong stimulus for, and an important
ingredient of,ingredient of, creativitycreativity..
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Uncertainty pervades scientific predictions about the
future performance of global and regional climates. Anduncertainties multiply when considering all the
consequences that might follow form an incomplete
understanding of how the physical climate works:
the effects of atmospheric aerosols on clouds
the role of deep ocean in altering surface heat
exchange
innate unpredictability of large, complex, andchaotic systems such as the global atmosphere and
ocean
consequence of humans being part of the future
being predicted
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There are three limits to science that we must recognize:
1. Scientific knowledge about climate change will
always be incomplete, and it will always be
uncertain. We must recognize that uncertainty and
humility should always be essential features of any
public policy debate which involves science, not least
climate change.
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2. We must recognize that beyond such normal
scientific uncertainty, knowledge as a publiccommodity will always have been shaped to some
degree by the processes by which it emerges into the
social world and through which it subsequently
circulates. The separation of knowledge aboutclimate change from the politics of climate change
a process that has been described as purification is
no longer possible. The more wider this is recognized
the better.
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3. We must be more honest and transparent about what
science can tell us and what it cant. We should nothide behind science when difficult ethical choices are
called for. We must not always defer to science or
to the voices of scientist when we need to make
decisions about what to do. These are decisions thatin relation to climate change will always entail
judgments beyond the reach of science.
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Science thrives on disagreement.
Science can only function through questioningand challenge. It needs the oxygen of
skepticism and dispute in order to flourish.
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If we are to understand climate change and if
we are to use climate change constructively
in our politics, we must first hear and
understand the discordant voices, those
multifarious human beliefs, values,
attitudes, aspirations, and behaviors. And,especially, we must understand what
climate change signifies for these important
dimensions of human living and humancharacter.
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Lets take a look at four contemporary and
contrasting ways (framings) of narrating the
significance of climate change just some
of the more salient discourses currently in
circulation.
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1. Climate change as a battlegroundbetween
different philosophies and practices of science,between different ways of knowing.
Climate change as scientific controversy is a
compelling discourse to which the media and
other social actors are readily attracted. Althoughthe controversy is allegedly about science, very
often scientific disputes about climate change
end up being used as a proxy for much deeper
conflicts between alternative visions of the futureand competing centers of authority in society.
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2. Climate change as justification for thecommodification of the atmosphere and,
especially, for the commodification of the gas,
carbon dioxide (CO2).
In this frame, climate change is viewed as the latest
rationale for converting a public common into aprivatized asset in this case, the global
atmosphere. Owner rights to emit CO2 are
allocated or auctioned between entities, alongside
the attendant machinery of the market whichprices and regulates the commodity.
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3. Climate change as the inspiration for a global
network of new, or reinvigorated, social
movements. Seeing climate change as amanifestation of the nefarious practices of
globalization, this framing warrants the emergence
of new forms of activism, both elite and popular,
to challenge these practices and to catalyze changein political, social and economic behavior.
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4. Climate change as a threatto ethnic, national, and
global security. The rhetoric associated with this
framing compares climate change (unfavorably)
with the threats posed by international terrorism,
warranting a new form of geo-diplomacy at the
highest levels of government. This framing led in
April 2007 to the first debate about climate change
to be held at the United Nations Security Council.
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Four important themes can be linked to climate:
1. Climate has both physicaland culturalmeaning.
Indeed, the idea of climate can only be fully
understood if one allows these physical and
cultural dimensions to interact and mutually shape
each other. Treating climate purely as a physicalentity, accessible solely through natural science
or, conversely, allowing the cultural symbolism of
climate to be detached from any physical anchors,
denies something essential about the idea ofclimate.
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2. Climate as ideology is used to carry and convey a
variety of ideological assumptions and
projections. This ideological baggage may not
always be obvious at the first sight. But the
literature contains many examples showing how
climate has been used to support, inter alia, the
ideologies of racism, the human mastery of
Nature, the sanctity of a pristine Nature, and the
preference for stability over change.
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3. Climate changes over time both the physical
climates of places, but also the ideologies with
which climate is associated.
Climate may change because its physical attributes
change or because its cultural symbolism changes,
or both.
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4. The story ofclimate change and human
civilization has also changed over time. The
dominant trope in this story has been one ofclimate change as threat, and yet dissenting voices
have emerged which emphasize the creative
potential for societies that can be found through
changes in climate. We cannot detach the storieswe tell about climate from the stories we tell about
societies. Disagreements about climate change are
as likely to reveal conflicts within and between
societies about the ideologies that we carry andpromote, as they are to be rooted in contrary
readings of the scientific evidence that humans are
implicated in physical climate change.
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The Scientific MethodThe Scientific Method Dogma is a principle, belief, or statement of
idea or opinion authoritatively considered to
be absolute truth. The essence ofscience is the observation of
nature.
Scientific observations must be repeatable.Repeatability tends to make science self-corrective.
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A hypothesis is an explanation for a
scientific observation.
According to Karl Poppers doctrine of
falsifiability, it is impossible to prove that a
hypothesis is true (Popper, 1959). Therefore, science advances by disproving
hypotheses, and the most valuable type of
scientific evidence is that which tends tofalsify hypotheses.
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As a simple example, consider the following
hypothesis: allswans are white. You cannot prove this hypothesis by observing
white swans. Even if you study swans for twenty
years and see a thousand white swans, this does
not prove that a singleblack swan does not existsomewhere.
In order to arrive at a unique conclusion, one must
therefore disprove all alternative hypotheses, not
prove a favored hypothesis.
Science operates by disproving hypotheses.
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A corollary to Poppers Doctrine of
falsifiability is that if a hypothesis is
incapable of falsification, it is not a
scientific hypothesis.
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Consider the contentious debate of
creationism vs. evolution. There are atleast three possible hypotheses:
1. The earth is young (few thousands
of years)
2. The Earth is young, but was created
by God to look old.
3. The Earth is old (billions of years)
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Both hypotheses 1 and 3 are capable ofbeing tested and potentially disproved.
Therefore, they are bothscientific
hypotheses. But, hypothesis number 2 cannot be
disproved, even theoretically. An
omnipotent Being cannot be outsmarted.
Therefore, hypothesis #2 is not a scientific
hypothesis. It is a dogma.
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PART I. Framework of ClimatePART I. Framework of Climate
ScienceScience What are the components of Earths climate
system?
How does climate change differ from day-to-dayweather change?
What factors drive changes in Earths climate?
How do the many parts of Earths climate system
react to these driving forces and interact? How do scientists study past climates and project
changes that lie in our future?
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Ch. 1Ch. 1
Overview of Climate ScienceOverview of Climate Science
This chapter surveys the factors that cause Earths
climate to change. It also reviews how the field of
climate science came into being, how scientists
study climate, and how an understanding of the
history of climate change helps to inform us about
changes looming in our near future.
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Scientists use the Celsius
and the Kelvin
temperature scales tomeasure climate changes.
Temperatures at Earths
surface vary mainly within
a small range of -50oC to
+30oC, just below and
above the freezing point
of water. Average is 150C
(590F)
(Unless otherwise noted,the figures and captions
are taken form Ruddiman,
2001)
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Weather and ClimateWeather and Climate Weather: is what is happening to the atmosphere at any
given time. It is characterized by the temperature, wind,precipitation, clouds, and other weather elements.
Climate: is what would be expected to occur at any giventime of the year based on statistics built up over manyyears. Climate varies from place to place, depending onlatitude, distance to the sea, vegetation, presence orabsence of mountains or other geographical factors.
Weather is what you get, climate is what you expect.
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Climate Variability and ClimateClimate Variability and ClimateChangeChange
Over the period of measurements of a
parameter (temp., rainfall, etc.), the averagevalue remains effectively constant (theseries is said to bestationary) but fluctuatesfrom observation to observation;
The combination ofclimate variability witha trend (e. g, cooling, warming, etc.)produces a climate change. (Fig. 1)
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Fig. 1. a) climate variability w/out any climate change; b) the same w/ a linear decline intemperature; c) climate variability w/ periodic variation of temp. of3oC; d) climatevariability w/ a sudden drop in temp. of4oC. (from Burroughs, 2001)
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Time scales of climate changeTime scales of climate change
(A) the last 300 million years, (B) the last 3 million years,
(C) the last 50,000 thousand years, and (D) the last 1,000
years. Here progressively smaller changes in climate at
successively shorter time scales are magnified out from
the larger changes at longer time scales.
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The Climate SystemThe Climate System It is an interactive system consisting of:
the atmosphere;
the hydrosphere;
the cryosphere;
the land surface;
the biosphere.
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Climate forcingsClimate forcings1. Tectonic processes generated by Earths internalheat. They are part of the theory of platetectonics (ex. the movements of continentsacross the globe, the uplift of mountain ranges,
and the opening and closing of ocean basins.2. Earth-orbitalchanges result from variations in
Earths orbit around the Sun. These orbitalchanges alter the amount of solar radiationreceived on Earth by season and by latitude.
3. Changes in the strength ofthe Sun also affect theamount of solar radiation arriving on Earth.
4. Anthropogenicforcingmeans the effect ofhumans on climate.
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Projected increase in continental runoff due to plant
responses to increasing carbon dioxide
Richard A. Betts et al. , Nature 448, 1037-1041 (30 August 2007)
In addition to influencing climatic conditions directly through radiative forcing, increasing carbon
dioxide concentration influences the climate system through its effects on plant physiology. Plant
stomata generally open less widely under increased carbon dioxide concentration, which reduces
transpiration and thus leaves more water at the land surface. This driver of change in the climate
system, which we term 'physiological forcing', has been detected in observational records of
increasing average continental runoff over the twentieth century. Here we use an ensemble of
experiments with a global climate model that includes a vegetation component to assess the
contribution of physiological forcing to future changes in continental runoff, in the context of
uncertainties in future precipitation. We find that the physiological effect of doubled carbon
dioxide concentrations on plant transpiration increases simulated global mean runoff by 6 per cent
relative to pre-industrial levels; an increase that is comparable to that simulated in response to
radiatively forced climate change (11 6 %). Assessments of the effect of increasing carbon
dioxide concentrations on the hydrological cycle that only consider radiative forcing will therefore
tend to underestimate future increases in runoff and overestimate decreases. This suggests that
freshwater resources may be less limited than previously assumed under scenarios of future global
warming, although there is still an increased risk of drought. Moreover, our results highlight that
the practice of assessing the climate-forcing potential of all greenhouse gases in terms of their
radiative forcing potential relative to carbon dioxide does not accurately reflect the relative effects
of different greenhouse gases on freshwater resources.
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Climate System Internal ResponsesClimate System Internal Responses
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Rates of Forcing versus ResponseRates of Forcing versus Response
Climate responses depend on the relative rate of changes in climate forcing versus the responsetime of the climate system (A) fast response times permit the climate system to fully track slowforcing. (B) slow response times allow little climate response to fast changes in forcing. (C, D)Roughly equal time scales of forcing and response allow varying degrees of response of the
climate system to the forcing.
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Cycles of forcing and responseCycles of forcing and response
Many kinds of climate forcing
vary in a cyclical way and
produce cyclic climate
responses. The amplitude of
climate responses is related to
the time allowed to attainequilibrium. (A) Climate
changes are larger when the
climate system has ample time
to respond. (B) The same
amplitude of forcing produces
smaller climate changes if theclimate system has less time to
respond.
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Variations in response time. An abrupt change in climate forcingwill produce climate responses ranging from slow to fast within different
components of the climate system, depending on their inherent response
times.
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Variations in cycles of response. If climate forcing occurs in
cycles, it will produce different cyclic responses in climate
system, with the fast responses tracking right along with the
forcing cycles while the slower cycles responses lag well behind.
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Feedback ProcessesFeedback Processes Essential to explaining and predicting climate change;
Positivefeedback: the original effect is reinforced by change of the
initial variable (ex: warming leads to a reduction in snow cover in
winter; this, in turn, could lead to more sunlight being absorbed at thesurface and yet more warming, an so on);
Negativefeedback: the original effect is dumped down by change of
the initial variable (ex: warming leads to more water vapor in the
atmosphere, which produces more clouds. These reflect more sunlight
into space thereby reducing the amount of heating of the surface and soend to cancel out the initial warming).
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Climate feedbacks
(A) Positive feedbackswithin the climate system
amplify changes initially
caused by external
factors.
(B) Negative feedbacks
mute or suppress the
initial changes
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Most common feedback processesMost common feedback processes
implied in climate changeimplied in climate change Ever-changing motions of the atmosphere
Variations in land surface (vegetation type,
soil moisture levels, snow-cover) Sea-Surface Temperatures (SSTs)
Extent of pack-ice in polar regions
Stately motions of the deep-ocean currentswhich may take over a thousand years tocomplete a single cycle
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Modern ClimateModern ClimateTheelectromagneticspectrum
Average solar
radiation on adisk and asphere
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Earths radiation budgetEarths radiation budget
Solar radiation arriving at the top of Earths atmosphere averages 342 Wm-2, indicating here as 100%(upper left). About 30% of the incoming radiation is reflected and scattered back to space, and theother 240 Wm-2 (70%) enters the climate system. Some of this entering radiation warms Earthssurface and causes it to radiate heat upward (right). The greenhouse effect (lower right) retains95%of the heat radiated back from Earths heated surface and warms by Earth by 31oC.
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Atmospheric Energy BalanceAtmospheric Energy Balance
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The Earths Energy BalanceThe Earths Energy Balance
In order to understand the Earths climatedriving processes, we must consider thefollowing:
i. the properties of solar radiation and also how theEarth re-radiates energy to space;
ii. how the Earths atmosphere and surface absorb orreflect solar energy and also re-radiates energy to
space; andiii. how all these parameters change throughout the year
and on longer timescales.
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The Earths Energy Balance (contd)The Earths Energy Balance (contd)
The radiative balance of the Earth can be defined
as:Over time the amount ofsolar radiation absorbed by theatmosphere and the surface beneath itis equalto the amount
ofheat radiation emitted by the Earth to space.
A body which absorbs all the radiation and, which
at any temperature, emits the maximum possible
amount of radiant energy is known as a black
body.
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The Earths Energy Balance (contd)The Earths Energy Balance (contd)
The temperature at the Suns surface is
about 6,000 K (about 5,276oC or 10,340oF).
If the Earth were a black body, the averageEarths surface temperature would be about
270 K (-3oC or 26oF). The observed average
value is 287 K (14o
C or 57o
F). Thedifference is due to the Greenhouse Effect.
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The AtmosphereThe Atmosphere
is the most unstableand rapidly changing
part of the system;
N2 (78.1%);
O2(20.9%); Ar(0.93%) Trace gases (CO2,
CH4, N2O, O3) =
greenhouse gases, less
than 0.1%
Water vapor (H2O),
1%, is also a GHG.
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Clouds influenceClouds influence
Albedo: the amount of solar radiation reflected
or scattered into space.
The mean global value is ~30%. It varies
between 5 90% (Table 2.1).
Clouds albedo varies between 40 - 90%.
Most clouds are bright reflectors of the
solar radiation and tend to cool
the climate system.
This phenomenon is called global dimming.
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Sun angle controls
heat absorption.
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Earths tilt and seasonalradiation
(A) The tilt of the Earthsaxis in its annualorbit around the Suncauses the northernand southernhemispheres to leandirectly toward theSun and then awayfrom the Sun at
different times of theyear
(B) This change inrelative positioncauses seasonal shifts
between thehemispheres in theamount of solarradiation received atEarths surface.
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Albedo-temperaturefeedback.
When climate cools,the increased extentof reflective snowand ice increases thealbedo of Earths
surface in high-latitude regions,causing furthercooling by positivefeedback. The same
feedback processamplifies climatewarming.
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Difference in heatingbetween land and ocean.
During the seasonal cycleof solar radiation (top),ocean surfaces heat andcool slowly and only by
small amounts becausetemperature changes aremixed through a layer 100m thick (lower left). Incontrast, land surfacesheat and cool quickly and
strongly because of theirlow capacity to conductand store heat (lowerright). (thermalinertia)
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Water vapor feedback. When climate warms, the atmosphere is able to holdmore water vapor (the major greenhouse gas in the atmosphere), and theincrease in water vapor leads to further warming by means of a positivefeedback. This feedback works in reverse during cooling.
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Sun Earth Relationship
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Global Atmospheric Circulation Model (GACM)
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Seasonal Pressure and Precipitation Patterns
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General circulation of the atmosphere. (Left) Heated air rises in the tropicsat the intertropical convergence zone (ITCZ) and sinks in the subtropics as part
of the large-scale Hadley cell flow, which transports heat away from the equator.Additional poleward heat transfer occurs along moving weather systems atmiddle and higher latitudes, with warm air rising and moving poleward and coldair sinking and moving equatorward. (Right) Evaporation vs. precipitation ascontrolled by latitude and general circulation of the atmosphere.
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Monsoonal circulation at largeMonsoonal circulation at large--scalescale
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Surface ocean circulation. The surface flow of the oceans is organized intostrong wind-driven currents. Currents moving out of the tropics carry heatpoleward, while currents moving away from the poles carry cold waterequatorward.
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Sinking of surface water. Warm salty water flowing northward inthe North Atlantic Ocean chills and sinks north of Iceland and in theLabrador sea. This cold deep water flows south of the Atlantic atdepths of 2 to 4 km. This processes is called the GreatOceanConveyor Belt.
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DeepDeep--ocean Circulationocean Circulation
Water filling theNorth Atlantic Basin
comes from sourcesin the high-latitudeNorth Atlantic, theSouthern Ocean nearAntarctica, and (atshallow depths) theMediterranean Sea.
The permanent
thermocline (100 -1000 m) separatescold deep water fromshallower layersaffected by changes inEarths surfacetemperature. Shallowseasonal thermocline(0-100 m) varies inresponse to seasonalsolar heating of theupper ocean layers.
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The Carbon CycleThe Carbon Cycle
The major carbon reservoirs on
Earth vary widely in size (A)
and exchange carbon at
different rates (B). Largerreservoirs (rocks, the deep
ocean) exchange carbon much
slower than smaller reservoirs
(air, vegetation, the surface
ocean)
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PhotosynthesisPhotosynthesis
On land In the ocean
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VegetationVegetation--Climate FeedbacksClimate Feedbacks
Vegetation-albedo feedback.When high-latitude climate cools,
replacement of spruce forest by
tundra raises the albedo of the land
in winter and causes additional
cooling (+ feedback).
Vegetation-precipitation feedback. Whenclimate becomes warmer, replacement of
grasslands by trees increases the release of
water vapor back to the atmosphere and
causes increases in local rainfall (+
feedback).
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Recent increases in
CO2 and CH4.There is an annual oscillation
(small drop in April-May and a
similar rise in the following
Sept.-Oct. The second trend in
the CO2 curve is its gradual
increase (burning of fossil-fuel,
deforestation).
The recent increase in CH4
concentration is likely due tohuman activities.
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CLIMATOLOGY
The Current Debate on the Linkage Between Global Warming andHurricanes
By J. MarshallShepherd andThomas Knutson, University ofGeorgia andNOAA
GeophysicalFluid DynamicsLaboratory (December 2006)
Following Hurricane Katrina and the parade of storms that affected theconterminous United States in 20042005, the apparent recent increase inintense hurricane activity in the Atlantic basin, and the reported increases inrecent decades in some hurricane intensity and duration measures in severalbasins have received considerable attention. An important ongoing avenue of
investigation in the climate and meteorology research communities is todetermine the relative roles of anthropogenic forcing (i.e., global warming)and natural variability in producing the observed recent increases in hurricanefrequency in the Atlantic, as well as the reported increases of tropical cycloneactivity measures in several other ocean basins. A survey of the existingliterature shows that many types of data have been used to describe hurricaneintensity, and not all records are of sufficient length to reliably identifyhistorical trends. Additionally, there are concerns among researchers about
possible effects of data inhomogeneities on the reported trends. Much of thecurrent debate has focused on the relative roles of sea-surface temperatures orlarge-scale potential intensity versus the role of other environmental factorssuch as vertical wind shear in causing observed changes in hurricane statistics.Significantly more research from observations, theory, and modeling isneeded to resolve the current debate around global warming and hurricanes.
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J P t t "B " f C t C t M th E i i
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Japanese Patent "Beano" for Cows to Cut Methane Emissions
by H.R. Downs - Jan 31st, 2008
Unless you live in a city or a big town, you see them everywhere, cows
Holsteins, Brahmas, Guernseys, Beefmasters, Limusins, or, if you happen tolive in Ethiopia, the aptly named Barka. Why aptly named? Becauseclimatologists estimate that cattle bark out an astounding amount ofgreenhouse gas, from both ends. You might call it the wind herd 'round theworld.
But cow flatulence is old news. Here's a sample of news from UN:
. . .livestock . . . accountsfor 9 per cent ofCO2 derivingfrom human-related
activities, but produces a much larger share ofeven more harmfulgreenhousegases. It generates 65 per cent ofhuman-related nitrous oxide, which has 296times the GlobalWarmingPotential(GWP) ofCO2. Most ofthis comesfrommanure.Andit accountsfor respectively 37 per cent ofallhuman-inducedmethane (23times as warming as CO2), which is largely produced by the digestive systemofruminants, and 64 per cent ofammonia, which contributes significantly toacid rain.
Earth is home to at least a billion and a half head of cattle. Thats more than allthe people living in India. And, the cattle population is growing in lock stepwith rising incomes, progress and development. The same U.N. reportpredicts:
Globalmeat production is projected to more than doublefrom 229 milliontonnes in 1999/2001 to 465 million tonnes in 2050, while milk outputis set toclimbfrom 580 to 1043 million tonnes. . .
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So what are we going to do with a billion and a half, 1,000 poundcreatures belching and crepitating us into global warming?
Beano for cows?
Junichi Takahashi, Ph.D., a Japanese scientist at Obihiro University ofAgriculture and Veterinary Medicine in Hokkaido, Japan may have theanswer, or at least part of the answer. Dr. Takahashi and friends havedeveloped a food additive that, they say, reduces bovine globalwarming intestinal gas to negligible levels.
The Takahashi team discovered this remedy quite by accident. They
noticed that pasture grass heavily fertilized with nitrates (not to beconfused with nitrites) triggered a marked reduction in methanegeneration in cattle; methane exacerbates global warming 20 timesmore than CO2.
Then, in the course of treating a mass poisoning in a herd of cattle, theveterinary team at Obihiro U. discovered that a combination of nitrates
and the amino acid cysteine not only reversed the poisoning but alsocut methane gas in the herd to trivial levels. Happily, this novel feedcut gases from both ends. No word on whether nitrous oxide levels arereduced by the additive but N2O is not emitted by the cow herself butrather from the ordure she so carefully places on the ground
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NY Times, February 8, 2008
Studies Deem Biofuels a Greenhouse Threat
By ELISABETH ROSENTHAL
Almost all biofuels used today cause more greenhouse gas emissions than conventional fuels if the fullemissions costs of producing these green fuels are taken into account, two studies being published
Thursday have concluded.The benefits of biofuels have come under increasing attack in recent months, as scientists took a closer look
at the global environmental cost of their production. These latest studies, published in the prestigiousjournal Science, are likely to add to the controversy.
These studies for the first time take a detailed, comprehensive look at the emissions effects of the hugeamount of natural land that is being converted to cropland globally to support biofuels development.
The destruction of natural ecosystems whether rain forest in the tropics or grasslands in South America not only releases greenhouse gases into the atmosphere when they are burned and plowed, but alsodeprives the planet of natural sponges to absorb carbon emissions. Cropland also absorbs far less carbonthan the rain forests or even scrubland that it replaces.
Together the two studies offer sweeping conclusions: It does not matter if it is rain forest or scrubland that iscleared, the greenhouse gas contribution is significant. More important, they discovered that, takenglobally, the production of almost all biofuels resulted, directly or indirectly, intentionally or not, in newlands being cleared, either for food or fuel. When you take this into account, most of the biofuel that
people are using or planning to use would probably increase greenhouse gasses substantially, saidTimothy Searchinger, lead author of one of the studies and a researcher in environment and economics atPrinceton University. Previously theres been an accounting error: land use change has been left out of
prior analysis.
These plant-based fuels were originally billed as better than fossil fuels because the carbon released whenthey were burned was balanced by the carbon absorbed when the plants grew. But even that equation
proved overly simplistic because the process of turning plants into fuels causes its own emissions forrefining and transport, for example.
The clearance of grassland releases 93 times the amount of greenhouse gas that would be saved by the fuelmade annually on that land, said Joseph Fargione, lead author of the second paper, and a scientist at the
Nature Conservancy. So for the next 93 years youre making climate change worse, just at the timewhen we need to be bringing down carbon emissions.
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The Intergovernment Panel on Climate Change has said that the world has to reverse the increase ofgreenhouse gas emissions by 2020 to avert disastrous environment consequences.
In the wake of the new studies, a group of 10 of the United Statess most eminent ecologists andenvironmental biologists today sent a letter to President Bush and the speaker of the House, NancyPelosi, urging a reform of biofuels policies. We write to call your attention to recent research
indicating that many anticipated biofuels will actually exacerbate global warming, the letter said.The European Union and a number of European countries have recently tried to address the land use
issue with proposals stipulating that imported biofuels cannot come from land that was previouslyrain forest. But even with such restrictions in place, Dr. Searchingers study shows, the purchase ofbiofuels in Europe and the United States leads indirectly to the destruction of natural habitats farafield.
For instance, if vegetable oil prices go up globally, as they have because of increased demand forbiofuel crops, more new land is inevitably cleared as farmers in developing countries try to get in
on the profits. So crops from old plantations go to Europe for biofuels, while new fields are clearedto feed people at home.
Likewise, Dr. Fargione said that the dedication of so much cropland in the United States to growingcorn for bioethanol had caused indirect land use changes far away. Previously, Midwestern farmershad alternated corn with soy in their fields, one year to the next. Now many grow only corn,meaning that soy has to be grown elsewhere. Increasingly, that elsewhere, Dr. Fargione said, isBrazil, on land that was previously forest or savanna. Brazilian farmers are planting more of theworlds soybeans and theyre deforesting the Amazon to do it, he said.
International environmental groups, including the United Nations, responded cautiously to the studies,saying that biofuels could still be useful. We dont want a total public backlash that would preventus from getting the potential benefits, said Nicholas Nuttall, spokesman for the United NationalEnergy Program, who said the United Nations had recently created a new panel to study theevidence.
There was an unfortunate effort to dress up biofuels as the silver bullet of climate change, he said.We fully believe that if biofuels are to be part of the solution rather than part of the problem, thereurgently needs to be better sustainability criterion.
Th E U i h h i 5 75 bi f l f b h d f
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The European Union has set a target that countries use 5.75 percent biofuel for transport by the end of2008. Proposals in the United States energy package would require that 15 percent of all transportfuels be made from biofuel by 2022. To reach these goals, biofuels production is heavilysubsidized at many levels on both continents, supporting a burgeoning global industry.
Syngenta, the Swiss agricultural giant, announced Thursday that its annual profits had risen 75
percent in the last year, in part because of rising demand for biofuels. Industry groups, like theRenewable Fuels Association, immediately attacked the new studies as simplistic, failing toput the issue into context.
While it is important to analyze the climate change consequences of differing energy strategies, wemust all remember where we are today, how world demand for liquid fuels is growing, and whatthe realistic alternatives are to meet those growing demands, said Bob Dineen, the groupsdirector, in a statement following the Science reports release. Biofuels like ethanol are the onlytool readily available that can begin to address the challenges of energy security andenvironmental protection, he said.
The European Biodiesel Board says that biodiesel reduces greenhouse gasses by 50 to 95 percentcompared to conventional fuel, and has other advantages as well, like providing new income forfarmers and energy security for Europe in the face of rising global oil prices and shrinking supply.
But the papers published Thursday suggested that, if land use is taken into account, biofuels may notprovide all the benefits once anticipated. Dr. Searchinger said the only possible exception hecould see for now was sugar cane grown in Brazil, which take relatively little energy to grow andis readily refined into fuel. He added that governments should quickly turn their attention todeveloping biofuels that did not require cropping, such as those from agricultural waste products.
This land use problem is not just a secondary effect it was often just a footnote in prior papers,.It is major. The comparison with fossil fuels is going to be adverse for virtually all biofuels oncropland.
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Ch. 2Ch. 2
Climate Archives, Data, and ModelsClimate Archives, Data, and ModelsClimate scientists use a wide range of techniques toClimate scientists use a wide range of techniques toextract, reconstruct, and interpret the history of Earthsextract, reconstruct, and interpret the history of Earthsclimate. Much of this history is recorded in four archives:climate. Much of this history is recorded in four archives:
sediments, ice, corals, and treessediments, ice, corals, and trees..
The interpretation of climate data is aided by the use ofThe interpretation of climate data is aided by the use ofclimate models to test hypotheses of climate change in aclimate models to test hypotheses of climate change in aquantitative way. In this chapter we describe physicalquantitative way. In this chapter we describe physical
models that simulate the circulation of Earths atmospheremodels that simulate the circulation of Earths atmosphereand ocean and then examine the concept behind modelsand ocean and then examine the concept behind modelsused to track mass movements of chemical tracers throughused to track mass movements of chemical tracers throughthe climate system.the climate system.
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Types of archivesTypes of archives
Sediments (cores, moraines, windblown loess)
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Lake cores. Hundreds of cores have been taken fromsmall lakes and analyzed for records of changes in
pollen (vegetation) and lake level over the last several
thousand years.
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Windblown loess. Strong
winds have deposited thick
layers of silt-size grains insoutheast China during the
last 3 million years. The
total thickness of these
loess deposits can each
several hundred meters. In
many regions people have
created homes in the loess
cliffs.
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Ocean drilling. Hundreds of ocean sediment cores are archives of past
climatic changes. The longest cores have been retrieved by drilling
operation on theJOIDES Resolution, run by the International Ocean
Drilling Program (IODP) at Texas A&M University.
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Ice ArchivesIce Archives
Ice cores retrieve climate records extending back thousands
ofyears in small mountain glaciers (A) to as much ashundreds of thousands ofyears in continent-sized ice-
sheets.
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Other Climate ArchivesOther Climate Archives
Layers of limestone in caves;
Trees;
Corals;
Historical archives of climate-related
phenomena
Instrumental records (only in last 100 to 200
years).
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Annual layering
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Climate Data (Climate Proxies)Climate Data (Climate Proxies)
Past vegetation. For oldergeologic intervals, climate on the
continents can be inferred from
distinctive vegetation. The remains
of trees similar to modern palms are
found in rocks from Wyoming
dating 45 millions years ago. Today
frigid winters in Wyoming would
kill palm trees.
Plankton:a proxy indicator
of climate in the ocean. CaCO3
shells of foraminifera (upper
left) and coccoliths (lower
left); SiO2 shells of diatoms
(upper right) and radiolaria
(lower right)
Pollen:a proxy indicator of
climate on land. For younger time
intervals, climate on land can be
reconstructed from changes in the
relative abundance of distinctive
types of pollen.
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Chemical weathering, transport, and deposition. Chemical weatheringslowly attacks rocks on land and sends dissolved ions into rivers for transport to the ocean.
Ocean plankton incorporate some of the dissolved ions in their shells, which fall to the seafloor
and form part of the geologic record. Some dissolved ions are also deposited in shallow
evaporating pools on continental margins where the climate dry.
Cli t M d lCli t M d l
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Climate ModelsClimate Models
Physical Climate ModelsPhysical Climate Models
Models of Earths climate are constructed to simulate present-day circulation. Thenchanges based on Earths history (different CO2 levels, ice sheet sizes, or mountainelevations) are inserted into the model, and simulations of past climates are run. Theclimate output is compared with independent geologic data to test the performance ofthe model.
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33--D General Circulation ModelsD General Circulation Models
(GCMs)(GCMs)GCMs incorporate the
basic physical laws and
equations that govern the
circulation of Earthsatmosphere: the fluid
motion of air;
conservation of mass,
energy, and other
properties; and gas laws
covering the expansion
and contraction of air.
ControlControl case simulationscase simulations
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ControlControl--case simulationscase simulations
GCMs are developed bytesting how well theyreproduce modern-dayclimate (temperature,
precipitation, and winds)based on present boundary
conditions (CO2,mountains, and land-seadistribution).
(A) observed Januarysurface temperatures
(B) model-simulatedvalues.
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Geochemical ModelsGeochemical Models
Geochemical models are used to follow the movements of Earths materials
(called geochemical tracers) through the climate system.Unlike physical circulation models, most geochemical models do not
reproduce the physical processes that govern the flow of air and water.
Instead, the models trace the sources, rates of transfer, and ultimatedepositional fate of two major components: sediment particles that result
from physical weathering (wind, water, and ice) , and dissolved ions
produced by chemical weathering (dissolution or hydrolysis).
Movements of tracers can be evaluated if they are not created or destroyed
by radioactive decay along the way.
Geochemical models can also trace exchanges of biogeochemical materials
such as carbon or oxygen isotopes that cycle back and forth among the
atmosphere, ocean, ice, and vegetation.
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OneOne--Way Transfer ModelsWay Transfer Models
The most basic kind of model tracks transfers of
material form its source or sources to the ultimate
sites of deposition, such as debris eroded from theland and deposited in ocean sediments.
If the material deposited has distinctive geochemical
characteristics, it can be analyzed and its abundance
quantified in term of a flux rate its rate of burial inthat sedimentary archive.
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One-Way Transfer. Geologists and geochemists often
need to distinguish the separate contributions of several
sources (usually linked to weathering of continental
rocks) to a single depositional archive (such as ocean
sediments).
S i ti t tif th t f i fl f i
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Scientists can quantify the rate of influx of ice-
rafted debris to high-latitude polar oceans by
extracting all sediment that is sand-size or largerand separating the mineral grains from the shells
of fossil plankton.
This analysis quantifies a process changes in theproduction and low of icebergs that is related to
climate.
The analysis can be carried a step further bycounting the ice-rafted debris under a microscope
to separate it into different types of grains (such
as volcanic debris, quartz, and limestone)
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The composition of these grains can provide a
general idea of source regions (for example, in
the North Atlantic, volcanic debris that came
form Iceland, and quartz and limestone that
came from Europe and North America). This level of analysis might tell climate
scientists which region within a particular
continent was the source of some of the grains.
A li d i i i if h
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A more complicated situation arises if the
material examined is fine-grained and has
been derived form multiple sources.
For example, fine silt and clay deposited in
the North Atlantic Ocean could have been
ice-rafted from North America or Europe,blown in from North Africa by dust storms, or
carried in deep currents from other sources.
Chemical Reservoirs
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Chemical Reservoirs
A different modeling approach is used for
geochemical tracers that are transported indissolved forms.
Mass balance models divide Earths systems
into reservoirs, including the atmosphere,ocean, ice, vegetation, and sediments.
The ocean is the most important reservoirs: it
receives almost all erosional products from thecontinents, it interacts with all of the other
reservoirs, and it deposits tracers in well-
preserved sedimentary archives.
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Geochemical reservoirs
and fluxes
Geochemical reservoirs are
like bathtubs with the
faucet and drain both left
partly open. The faucet
delivers the input flux, the
drain takes away the outputflux, and the balance
between the input and the
output determines the water
level in the tub (reservoir).
At steady state, input and
output are in balance and
the water level in the tub
remains constant.
The residence time is the time it takes for a
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The residence time is the time it takes for a
geochemical tracer to pass through a reservoir.
In the tub analogy, the residence time is thetime the average molecule of water takes to
pass from the faucet to the drain.
For a reservoir at steady state (a tub with anunchanging water level), the residence time is
residence time= reservoir size/flux rate in/out
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ReservoirReservoir--Exchange ModelsExchange Models
The methods discussed to this point have
been based on one-way mass transfers in
which geochemical tracers leave the
interactive climate system by being buried in
seafloor sediments and isolated out of touch
with other reservoirs for millennia.
Another important exchange is the movementof a geochemical tracer back and forth
between two (or more) reservoirs.
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Reservoir exchangemodels. Some
geochemical models are
designed to track
reversible exchanges of
important components
such as water and carbon
as they cycle between
smaller reservoirs such as
ice sheets and vegetationand the larger ocean
reservoir.
One example is the transfer of water between
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One example is the transfer of water between
the ocean and ice sheets on orbital time
scales.
Exchanges of water between the relatively
small reservoir stored in ice sheets on land
and the much larger reservoir left behind inthe ocean can be tracked by using the fact
that the isotopic composition of oxygen in the
H2O molecules in ice sheets is different from
the average composition of the ocean in
shells of plankton provide a way to estimate
past changes in the volume of ice stored on
land.
Another useful application of reservoir-exchange
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Another useful application of reservoir-exchange
analysis examines fluxes of carbon among its many
reservoirs. Fluxes of carbon between the relatively small
reservoir of carbon stored in land vegetation and the
much larger carbon reservoir in the ocean can be
tracked using the fact that terrestrial carbon has acarbon isotope ration distinctively different form that
of marine carbon.
Net transfers of terrestrial carbon from land to sea can
be detected by examining the average carbon isotopecomposition of the ocean recorded in the shells of
calcite organism buried in ocean sediments.
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Other types of modelsOther types of models
Reservoir-Exchange Models track a single geochemicaltracer as it moves back in forth between two or morereservoirs (ex., transfer of water between the ocean and icesheets on orbital time scales).
Ocean GCMs are similar in construction to atmosphericGCMs.
Ice-sheet Models
Vegetation Models
Time-Dependent Models
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Part II. TectonicPart II. Tectonic--Scale ClimateScale Climate
ChangeChange Why has Earth remained habitable throughout its entire
recorded history?
What explains the changes in Earths climate over the last
several hundred million years? Why was Earth ice-free even at the poles 100 Myr ago?
What are the causes and climatic effects of changes in sealevel through time?
How did the apocalyptic asteroid impact 65 Myr ago affectclimate?
What causes Earths climate to cool over the last 55 Myr?
hh
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Ch. 3Ch. 3
COCO22 and Longand Long--Term ClimateTerm Climate Why is Earth habitable? Because
Our Sun is just the right distance from Earth
GHG warm Earths climate by 31
o
C Why Earth has remained habitable for most of its
4.55 billion years of existence, even though our
Sun was much weaker at the beginning? Because
Our planet had/has a kind ofnaturalthermostatcontrolling thegreenhouse eras as wellas icehouse
eras.
Wh i V h t?Wh i V h t?
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Why is Venus hot?Why is Venus hot?
(A) Venus receives almost twice as much as solar radiation as (B) Earth, but its
dense cloud cover permits less radiation to penetrate to its surface. Yet Venus is
much hotter than Earth because of its CO2-enriched atmosphere creates a much
stronger greenhouse effect that traps much more heat.
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The Faint Young Sun ParadoxThe Faint Young Sun Paradox
Models indicate that theyoung Sun shone 25% to30% more faintly than
today; In such conditions, an
early Earth would haveremained completelyfrozen for the first 3 Byr.
Primitive life-forms dateback to at least 3.5 Byrago.
Climate DebateClimate Debate
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Climate DebateClimate Debate
A Snowball Earth?A Snowball Earth?
Evidence of several glaciations (2 - 4 icehouse episodes) between 850 and550 Myr ago is found on Earths modern-day continents. If theseglaciated regions were located at or near the polar regions, climate mayhave been little different from what it is today. But if they were locatedin the tropics, a snowball Earth may have existed.
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The Earths ThermostatThe Earths Thermostat
Warmed the Earth very early when
otherwise our planet would have frozen
under a weak young Sun Cooled the Earth when Sun became hotter.
WHO/WHAT DID IT?
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maybe GHG, if they were more maybe GHG, if they were more
abundant earlier in Earths historyabundant earlier in Earths history
and subsequently decreased inand subsequently decreased inabundance?abundance?
But HOW?
C b E h b t R kC b E h b t R k
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Carbon Exchanges between RocksCarbon Exchanges between Rocks
and the Atmosphereand the Atmosphere (A) The largest reservoir
of carbon on Earth lies in
its rocks.
(B) Over intervals ofmillion of years, slow
exchanges among the rock
and ocean/vegetation/soil/
/atmosphere reservoirs cancause large changes in
atmospheric CO2 levels.
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CO2 enters Earths atmosphere from deep in its interior
through release of gases in volcanoes and at hot springssuch as those found today at Yellowstone National Park inWyoming.
Removal of CORemoval of CO22 from the Atmosphere by Chemicalfrom the Atmosphere by Chemical
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Removal of CORemoval of CO22 from the Atmosphere by Chemicalfrom the Atmosphere by Chemical
WeatheringWeathering
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HydrolysisHydrolysis
is the main mechanism for removing CO2 from
the atmosphere;
Three main ingredients in the process are:1. The minerals that make up typical continental
rocks;
2. Water derived from rain;3. CO2 derived from the atmosphere.
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Chemical weathering of silica-rich rocks on the continents
removes CO2 from the atmosphere, and part of the carbon
is later stored in the shells of marine plankton and buried in
ocean sediments.
Di l iDi l i
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DissolutionDissolution
It is important to distinguish weathering of
silicates by hydrolysis from dissolution.
Dissolution is the familiar process that eatsaway limestone in caves.
Cli t t l h i lCli t t l h i l
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Climate controls on chemicalClimate controls on chemical
weatheringweatheringTemperature (A) and
precipitation (B) both
show a general trend from
high values in warmer lowlatitudes to low values in
colder high latitudes. The
total amount of vegetation
produced per year increase
with temperature (C), as
well as with precipitation
Is Chemical Weathering EarthsIs Chemical Weathering Earths
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Is Chemical Weathering EarthsIs Chemical Weathering Earths
Thermostat?Thermostat?Negative feedback from
chemical weathering
Chemical weathering acts
as a negative climate
feedback by reducing the
intensity of both (A)
imposed climate warming
and (B) imposed climatecooling.
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Earths Thermostat?Earths Thermostat?
(A) The most plausibleexplanation of the faintyoung Sun paradox isthat the weakness ofthe early Sun wascompensated for by a
stronger carbongreenhouse in theatmosphere.
(B) When the Sun laterstrengthened, increasedchemical weatheringdeposited the excessgreenhouse carbon inrocks, and thegreenhouse effectweakened enough tokeep Earthstemperature moderate.
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Water vapor feedbackWater vapor feedback
When climate warms, the
atmosphere is able to hold
more water vapor, which is
the major greenhouse gas in
the atmosphere. The
increase in water vapor
leads to further warming by
means of positive feedback.
This feedback works in the
same way (but oppositedirection) during cooling.
L ki D i t Cli t S iL ki D i t Cli t S i
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Looking Deeper into Climate ScienceLooking Deeper into Climate Science
The Organic Carbon SubcycleThe Organic Carbon Subcycle
About 20% of the carbon thatmoves between Earths surfacereservoirs (air, water, andvegetation) and its deep rockreservoirs does so in theorganic carbon cycle.Photosynthesis on land and in
the surface ocean turnsinorganic carbon into organiccarbon, most of which isquickly returned to theatmosphere or surface ocean. Asmall fraction of the organiccarbon is buried in continentaland oceanic sediments thatslowly turn into rock. Thiscarbon is eventually returned to
the atmosphere as CO2, eitherby erosion of continental rocksor by melting and volcanicemissions.
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G i h p th iG i h p th i
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Gaia hypothesisGaia hypothesis
Over time, life-forms
gradually developed in
complexity and played a
progressively greater
role in chemical
weathering and itscontrol of Earths
climate. In the extreme
form of the Gaia
hypothesis, life evolved
for the purpose of
regulating Earths
climate.
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Supporters vs. critics of Gaia hypothesisSupporters vs. critics of Gaia hypothesis
Chemical weatheringthermostat directly involvesthe action of life-forms:
(1)carbon is the basis of theCO2 cycle;
(2)Photosynthesis;
(3) role of shell-bearingplankton in extracting CO2
from the ocean and store itin their CaCO3 shells.
Many of the active rolesplayed by organisms inthe biosphere today are arelatively recent
developments in Earthshistory and the role of lifein the distant past was
probably negligible;
The very late appearance ofshell-bearing oceanicorganisms near 540 Myrago means that life hadno played obvious role inchemical weathering.
The Revenge of GaiaThe Revenge of Gaia Earths ClimateEarths Climate
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The Revenge of GaiaThe Revenge of Gaia Earth s ClimateEarth s Climate
in Crisis and the Fate of Humanityin Crisis and the Fate of Humanity This is the last book published by Dr. James E. Lovelock in July 2006.
James Lovelock- father of climate studies and originator of the influentialGaia theory which views the entire earth as a living meta-organism-provides adefinitive look at our imminent global crisis. In this disturbing new book,Lovelock guides us toward a hard reality: soon, we may not be able to alter the
oncoming climate crisis. Lovelocks influential Gaia theory, one of thebuilding blocks of modern climate science, conceives of the Earth, includingthe atmosphere, oceans, biosphere and upper layers of rock, as a single livingsuper-organism, regulating its internal environment much as an animalregulates its body temperature and chemical balance. But now, says Lovelock,that organism is sick. It is running a fever born of the combination of a sunwhose intensity is slowly growing over millions of years, and an atmospherewhose greenhouse gases have recently spiked due to human activity. Earth will
adjust to these stresses, but on time scales measured in the hundreds ofmillennia. It is already too late, Lovelock says, to prevent the global climatefrom "flipping" into an entirely new equilibrium state that will leave thetropics uninhabitable, and force migration to the poles. The Revenge ofGaiaexplains the stress the planetary system is under and how humans arecontributing to it, what the consequences will be, and what humanity must doto rescue itself.
Ch 4 Plate Tectonics and LongCh 4 Plate Tectonics and Long
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Ch. 4 Plate Tectonics and LongCh. 4 Plate Tectonics and Long--
Term ClimateTerm ClimateThe last 550 Myr of Earths history are far better known than the first 4
billion years (the locations of continents and the shapes of the oceanbasins are clearer; better-preserved sedimentary rock archives; betterstudied fluctuations between icehouse intervals and greenhouseintervals).
First we examine how plate tectonics work. Next we explore thepossibility that icehouse intervals occur because plate tectonics motioncause continents to drift across cold polar regions. Then we climatemodels to investigate the range of factors that controlled climate 200Myr ago. These investigations reveal that changes in atmospheric CO2levels are needed to explain the sequence of changes from icehouse to
greenhouse conditions over the last 550 Myr. Finally, we evaluate twohypotheses that link changes in plate tectonic processes to changes inCO2 levels.
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Increasingly wellpreserved sedimentaryrock archives holdabundant evidence ofpast climates,including a sequence
of alternationsbetween icehouseintervals andgreenhouse intervals
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Earths structureEarths structure
Earths outer layers can be
subdivided in two ways.
The basalts of the ocean
crust and the granites in
continental crust differ fromeach other and from the
underlying mantle in
chemical composition. As
physical behavior, the
lithosphere that forms the
tectonic plates is hard, rigidunit, whereas the underlying
asthenosphere is softer and
capable of flowing slowly.
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Tectonic platesTectonic plates
Earths lithosphere is divided into a dozen major tectonic
plates and several smaller plates, which move as rigid units in
relation to one another, as the arrows indicate.
Plate Tectonics and Glaciations:Plate Tectonics and Glaciations:
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The Polar Position HypothesisThe Polar Position Hypothesis
The long-term changes are due tolatitudinalposition controlling theglaciations on continents.
After450 Myr ago, plate tectonics activitycarried the southern continent of Gondwana
across the South Pole on a path headedtoward continents scattered across thenorthern hemisphere. Subsequent collisionsformed the giant continent Pangaea.
Changes in the position of the south magneticpole in relation to the Gondwana continent
were caused by the slow movement ifGondwana across a stable pole. Glaciationsoccurred in the northern Sahara about 430Myr ago as well as in S. Africa, Antarctica, S.America, and Australia
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Polar Position HypothesisPolar Position Hypothesis
It made two key predictions that can be
tested over the younger part of the Earths
history:(1) ice sheets should appear on continents that were
located at polar or near-polar latitudes, but
(2) no ice should appear if the continents were located
outside polar regions
Evaluation of the Polar Position Hypothesis of
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yp
Glaciation
Time (Myr ago) Ice sheetspresent?
Continents inpolar position?
Hypothesissupported?
440 Yes Yes Yes
425-325 No Yes No
325-240 Yes Yes Yes
240-125 No No Yes
125-35 No Yes No
35-0 Yes Yes Yes
GlaciationsGlaciations --ExamplesExamples
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Northern Africa (440 Myr ago)
Central Park, NYC
Tectonic Control of COTectonic Control of CO22 Input:Input:
The BLAG Spreading Rate Hypothesis (R.The BLAG Spreading Rate Hypothesis (R. BBerner,erner,
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The BLAG Spreading Rate Hypothesis (R.The BLAG Spreading Rate Hypothesis (R.BBerner,erner,
A.A. LaLasaga, R.saga, R. GGarrels, 1983)arrels, 1983)
The climate changes during the last severalmillion years have been driven mainly bychanges in the rate ofCO2 input to theatmosphere (and ocean) by plate tectonics
processes.
CO2 is transferred from rocks in Earths
interior to the atmosphere-ocean systemmainly at two kinds of plate margins: oceanridges (top left) and subduction zones (topand bottom right). A small input of CO2occurs when volcanoes erupt at hot spots inthe middle of plates (bottom left)
The BLAG spreading hypothesis asserts thatatmospheric CO2 and global climate are
driven by the global mean rate of sea floorspreading, which controls the global rate ofCO2 input at ocean ridge crests andsubduction zones.
Convergent Margins: IndiaConvergent Margins: India--AsiaAsia
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Convergent Margins: IndiaConvergent Margins: India AsiaAsia
CollisionCollision
k fk f
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Breakup of PangaeaBreakup of Pangaea
Seafloor Spreading and PlateSeafloor Spreading and Plate
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Seafloor Spreading and PlateSeafloor Spreading and Plate
BoundariesBoundaries
The BLAG hypothesisinvokes chemical weatheringas a negative feedback that
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as a negative feedback thatpartially counters the changesin atmospheric CO2 and
global climate driven bychanges in rates of seafloorspreading.
In the BLAG hypothesis,carbon cycles continuouslybetween rock reservoir andthe atmosphere: CO2 isremoved from the atmosphere
by chemical weathering onland, deposited in the ocean,subducted, and returned tothe atmosphere by volcanicactivity.
Tectonic Control of COTectonic Control of CO22 Removal:Removal:
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Tectonic Control of COTectonic Control of CO22 Removal:Removal:
The Uplift Weathering HypothesisThe Uplift Weathering Hypothesis
Developed by Maureen Raimo and her colleagues in the late 1980s.
They consider the chemical weathering as the active driver of climate change,rather than a negative feedback that moderates climate changes.
The BLAG hypothesis views chemical as responding to three climate-relatedfactors: temperature, precipitation, and vegetation.
The uplift weathering hypothesis asserts that the global mean rate of chemicalweathering is heavily affected by the availability of fresh rock and mineralexposure that the weathering process can attack, and that this exposure effectcan override the combined effects of the three climate-related factors both insome regions and globally.
Examples: The Wind River Basin of Wyoming; The Amazon River Basin
The uplift is caused by two kinds of tectonic processes: a. subduction of ocean
crust underneath continental margins, and b. the collision of continents (ex.,the Tibetan Plateau, 55 Myr ago)
Ch 5 G h CliCh 5 G h Cli
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Ch. 5 Greenhouse ClimateCh. 5 Greenhouse Climate
Evidence shows that 100 Myr ago the Earth was warmenough at the poles to keep ice sheets from forming thiswas a real greenhouse world!
Do climate models simulate the warmth of this greenhouse
climate? And if so, did a high level of atmospheric CO2 cause it?
What lessons this past greenhouse world holds for ourfuture climate?
Why sea level 100 Myr ago was some 200 m higher than it
is today? What happened 65 Myr ago to change the climate and
environment?
What Explains the Warmth 100 Myr Ago?What Explains the Warmth 100 Myr Ago?
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What Explains the Warmth 100 Myr Ago?What Explains the Warmth 100 Myr Ago?
The world 100 Myr ago. By 100 Myr ago, plate tectonic
processes had broken the supercontinent Pangea into separate
smaller continents that were flooded by shallow seas.
Evidence of greenhouse warmth 100 Myr agoEvidence of greenhouse warmth 100 Myr ago
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Evidence of greenhouse warmth 100 Myr agoEvidence of greenhouse warmth 100 Myr agoVegetation and animals
that appear to have beenwarm-adapted lived in
both polar regions 100Myr ago:
(A) fossils of breadfruittrees like those that livetoday in the tropics;
(B) Dinosaurs, many of
which lived poleward ofthe Arctic and Antarcticcircles.
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Cretaceous target signal. Climate scientists have
used geologic data (faunal, floral, and geochemical)to compile an estimate of temperatures 100 Myr ago.
Temperature were warmer than they are today at all
latitude, especially in polar regions.
What Explains Greenhouse Warmth 100 Myr ago?What Explains Greenhouse Warmth 100 Myr ago?
Climate Model SimulationClimate Model Simulation
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Climate Model SimulationClimate Model Simulation
What Explains the Data-ModelMismatch?
PossibleProblems with the Data
a. fossil organisms may be differentfrom their modern counterparts.
b. fossil under-representation
c. postdepositional alteration ofmaterials in the geologic record.
PossibleProblems with the Model
a. the treatment of oceancirculation is still very crude.
b. the effects of clouds on climateis not fully understood.
The Cretaceous ocean could haveoperated in a fundamentallydifferent way from the present-dayocean (ocean heat transporthypothesis).
What Explains Greenhouse Warmth 100 Myr ago?What Explains Greenhouse Warmth 100 Myr ago? (contd.)(contd.)
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What Explains Greenhouse Warmth 100 Myr ago?What Explains Greenhouse Warmth 100 Myr ago? (contd.)(contd.)
Sea Level Changes (Eustatic Changes)Sea Level Changes (Eustatic Changes)
Transgression (rise of the sea level) may cause warm climates by moderating the harshwinters
vs.
Regression (fall of the sea level) may cause cold climates of continental conditions.
Causes of TectonicCauses of Tectonic--Scale changes inScale changes in
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gg
Sea LevelSea Level Reading assignment: p. 86-92
Asteroid Impacts orAsteroid Impacts or
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pp
Why Did the Dinosaurs disappeared 65 Myr ago?Why Did the Dinosaurs disappeared 65 Myr ago?
A. Ocean sediments
containing a layer enriched
in the element iridium are
evidence of a large asteroidimpact 65 Myr ago.
B. Sediments deposited in
Montana 65 Myr ago
contain grains of quartzcrisscrossed by multiple
lineations produced by high-
pressure shock waves from
an asteroid impact.
Asteroid Impacts orAsteroid Impacts or
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pp
Why Did the Dinosaurs disappeared 65 Myr ago?Why Did the Dinosaurs disappeared 65 Myr ago?
Mexicos YucatnPeninsula has a circulararea more than 200 km indiameter that is a goodcandidate for the site of
the asteroid impact 65Myr ago. The patternshown is a result ofmeasurements of Earthsgravity that can detectlow-density pulverized
rock (in blue) and higher-density rock (in green andyellow).
Asteroid Impacts orAsteroid Impacts or
Why Did the Dinosaurs disappeared 65 Myr ago?Why Did the Dinosaurs disappeared 65 Myr ago?
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Why Did the Dinosaurs disappeared 65 Myr ago?Why Did the Dinosaurs disappeared 65 Myr ago?
The asteroid impact 65 Myr ago is sought to have had major effects on Earths
environment, including the extinction of over two-thirds of the species then alive.
The likely climatic effects vary with the amount of elapsed time after the initial
impact and appear to have been restricted to a few centuries.
Relevance of Past GreenhouseRelevance of Past Greenhouse
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Climate to the FutureClimate to the Future CO2 levels varied from 100 ppm to 1,400 ppm.
The pre-industrial level of CO2 was 280 ppm.
At low (1,000 ppm) CO2 values, it will reduce
the amount of s snow and ice present at highlatitudes
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CO2 saturation: As CO2 concentrations
rise, the atmosphere gradually reaches the
point at which further CO2 increases havelittle effect in trapping additional back
radiation from Earths surface.
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Water vapor feedback: A warm
atmosphere with CO2 values of 1,000 ppm
can hold much more water vapor than acold atmosphere with values of 100 ppm.
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Effect ofCO2 on global temperature. Climate model simulations ofthe effects of changing atmospheric CO2 levels on global temperature show
greater warmth for higher CO2 concentrations.
Large and abrupt greenhouseLarge and abrupt greenhouse
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g gg g
episode near 50 Myr agoepisode near 50 Myr ago
Unusual warmth 55 Myr
ago. A pulse of unusual
warmth that developed near55 Myr ago and persisted for
tens of thousands of years
warmed the deep ocean by
several degrees Celsius.
Gas hydrate decomposition!
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Ch. 6Ch. 6
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Back into theBack into the IcehouseIcehouse The Last 55 Million YearsThe Last 55 Million Years
Oxygen Isotope DataOxygen Isotope Data
B th 16O d 18O t bl ( di ti )
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Both 16O and 18O are stable (nonradioactive)
isotopes of oxygen that occur naturally in Earthswater and air.
The ratio 18O/ 16O }or 0.0025.
Climate scientists who analyze the CaCO3shells
of foraminifera in the oceans measure small
variations around this average value.
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In the modern ocean, typical H18O values vary from 0 to -
2 in warm tropical surface waters to as much as +3 to
+4 in cold deep ocean waters. In present-day ice sheets,in contrast, typical H18O values reach -30 in Greenland
and -55 in Antarctica.
The isotopic composition of oxygen from ocean waterrecorded in foraminifera shells has changed over time,mainly in response to two important climate related
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top related