Global Change_I-II.pdf

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GLOBAL CHANGE

o .

oEarth has changed in the past.

oEarth will change in the future.

oHow will this affect us?

Introduction

oEarth is changing probably faster today than it has

in the past.

Mostly due to human activity (anthropogenic).

Most clearly seen in the atmosphere.

Also in forests, mountains, lakes, rivers and

oceans etc.

Some effects detrimental to the environment

oca , reg ona an g o a


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oGlobal environmental issues that we will discuss:

o a warm ng

-different than greenhouse effect

Ozone hole over Antarctica

Deforestation and loss of Biodiversity

What needs to be done

.

o Knowledge of the scientific problems is

essential for taking right and intelligent

decisions.

o At times the decision ma be costl .


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2. Past global change:

o

before humans came on the scene.

o Need to look at the past records to distinguish

between natural and anthropogenic change.

o Climate records show overlapping of both short

term man made and lon term chan es.

o Need to understand how and why climate has

changed in the past.o Is the Earth cooling or heating up?


3. Systems approach:

o To treat Earth as a system of interrelated and

interacting components: the atmosphere, the

hydrosphere, the biota and the solid Earth

o To understand how different components

interact in response to external influences, or

forcings.


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Geosphere

Global Change on short time scales

Global Warming

oGreenhouse effect-A natural process wherein gases

absorb outgoing infrared radiation (IR or radiant heat) and

reradiate it back to the Earths surface. It makes the Earth

warmer because of the atmosphere.

oGlobal warmin - a warmin of Earths atmos here that is

due to an anthropogenic enhancement of the greenhouseeffect by releasing certain gases through a combination of

industrial and agricultural activities.


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Global Change on short time scales

Global Warming

oThe issue has been controversial.

oDifficult to separate the anthropogenic signal from

natural ones.

Global Change on short time scalesEvidence of Global Warming

oThere are clear evidence of global warming.

Intergovernmental Panel on Climate Change (IPCC)

2007 report

Increase in air and ocean temperatures

Widespread melting of snow and ice

Rise in global average sea level


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Mauna Loa CO2

concentrations

Keeling Curve

began from 1958

Charles David Keeling

(19282005)

Overall increase of ~1.4 ppm/yr

Rate of increase is faster in the recent past (0.7ppm/yr in the early 1960s to 1.9 ppm/yr over the last

decade.

Keeling Curve: Updated

https://scripps.ucsd.edu/programs/keelingcurve/


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Overall increase of ~1.4 ppm/yr

Rate of increase is faster in the recent past (0.7 ppm/yr in the

early 1960s to 1.9 ppm/yr over the last decade.


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Increase in atmospheric CO2

oEvidence that atmospheric CO2 is increasing is

indis utable.

oHas been confirmed in many stations in the world.

oRange in seasonal fluctuations vary.

oMostly caused by combustion of coal, oil and

natural gas, partly by tropical deforestation

How do we know this??


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oWhen did the increase

begin?

Ice core records

oNeed to go to records

before human impact.

oNote the concurrence

between ice core records

and direct measurements.

oPreindustrial CO concentration (at ca. 1800) was ~280 ppm.

Today, it is about 400 ppm.oCO2 build up started well before Industrial Age (around 1850)

oIncrease between 1800-1850 is attributed to deforestation in North

America

oCalled the pioneer effect.


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Preindustrial CO2concentration (at ca. 1800) was ~280 ppm. Today, it is about 390

ppm.

The concentrations of greenhouse gases are

definitely increasing!!!

So what???

Is it affecting us?

Has it changed the climate?


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Change in surface temperature

oHas the increase in greenhouse gases caused a rise intemperature?

oThe answer is Yes! as per IPCC.

oData of recording stations (meteorological stations) over 100

years, show consistent increase in atmospheric temperature.

oSimilar trends shown by SST measurements carried out by

ships.

Average surface temperature as deviations from 19611990 mean value.

IPCC Assessment Report 2007

Goddard Institute for Space Studies(GISS), National Climatic Data Center (NCDC ) NOAA,

Climatic Research Unit at the University of East Anglia (CRUTEM)


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Change in surface temperature

oSurface temperature has increased by about 0.8C since

1900.

oThis increase is expected from 40% increase in atmospheric

CO2 as seen earlier.

oBut temperature does not increase as uniformly as CO2 and

rates of increase differ. Climate is also influenced by other

.

oThere could be problems with temperature records.

oMeteorological stations are located more in the cities. This

Records of global surface temperature

records. Scientists try to account for this effect, removal of this

effect can not be very accurate.

oUncertainty in the SST measurements.

oThe way measurement is done

oSatellite measurements will improve records in future


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Records of global surface temperature

oCoverage in time and space. Several decades of reliable

measurements are needed for establishing accurate trends.

oIn spite of this, 0.8C increase seems real.

oThe cause needs to be understood.

Causes and problems of temperature change

o Is the recent warming a recovery from Little Ice Age

(1500-1850)? Underscores the importance of looking at the

ast records to redict the future.

o During the period between the 1940 and 1970, warming

stopped. Northern hemisphere temperature declined.

o This may have been caused by sulfate aerosols that enter

the atmosphere from coal fired power plants.

o Coal burning also releases CO2 and should contribute to

global warming.


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Causes and problems of temperature change

o We now scrub the SO2 from coal plant emissions to protect

a es an r vers rom ac ra n.

o Removal timescales of SO2 (few weeks) and CO2 (decades)

are different, CO2 effect is cumulative. Need for awarenessof time scale of global change.

Effect of global warming

Changes in the cryosphere

.oIn Alaska, the warming has been nearly 3C in the

last century.

oDramatic effects on the extent of sea ice in the

Arctic Ocean.


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Source: NASA. The yellow outline shows the average sea ice minimum from 1979.


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oThe Northwest Passage is open a few weeks each year

oShould facilitate trade between Europe and the Americas

oProblem for polar bears and local inhabitants

oIncreased melting of Greenland ice sheets (thicker and

hence slower to melt) would raise sea level adverse effect

on continental coast lines

o o e: e me ng o rc c sea ce oes no cause c angein the sea level)


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oRise in sea level

oTropical pests

oIntensity of tropical hurricanes



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Ozone Hole

Stratospheric ozone absorbs harmful UV rays.

Ozone depletion can have adverse effect on life.

oFirst discovered in 1985 over Antarctica.

oObserved in yearly ozone concentration above Halley

Bay.

oThe ozone level during October dropped by halfbetween 1975 and 1990.


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Ozone Depletion

oMostly caused by chlorine compounds

namely chlorine monoxide, ClO.

oInside the hole, ozone levels were more than

were 15 times higher

http://www.antarctica.ac.uk/met/jds/ozone/images/zminoct nocurve.JPG


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Deforestation and loss of biodiversity

oHumans switched from hunters/gatherersto farmers.

oLoss of vegetation leads to loss of plant

species, dependent animals and

microorganisms.

oBiodiversity reduced.

oMost significant in tropical rain forests

(loss rate is ~1.8% per year).

oExtinction of species and loss of genetic

information.

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