impactul schimbărilor climatice asupra geochimiei mediului 2

8/8/2019 Impactul schimbrilor 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.



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pp


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).




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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

8/8/2019 Impactul schimbrilor climat

impactul schimbărilor climatice asupra geochimiei mediului 2

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