the science of climate change

The Science of Climate Change

Explaining why we need to act NOWPrepared with material from NPL (UK), IPCC, BOM (Aus)

Australian Institute of Physics (Vic branch) Education Committee


What is climate change?

Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer).1



• Has Climate change occurred before?

YES!



How do we know Climate Change has occurred before?


The Foot-print of Glaciers

•Geologists wondered why large boulders occurred in landscapes were they didn’t belong•The shapes of some valleys were U shaped rather than V shape. •Striations (scratches) on rocks


So why do Ice Ages Occur?

The ice ages are believed to be caused by a phenomena called ‘Orbital Forcing’.



Why are Ice Ages important in this discussion?

The ice ages are part of a cycle where the Earth warms and then cools.

Ice ages and CO2 in the atmosphere follow each other




Ice Ages



0

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400

050100150200250300350400

CO

2 (

ppm

v)

Thousands of years before the present

Ice Ages


How do we know about the atmosphere 100,000 years ago?




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050100150200250300350400

CO

2 (

ppm

v)

Thousands of years before the present

Minimum Value

180 ppm

Maximum Value

300 ppm


• So if this has been happening for ages why are we worried now?




0

50

100

150

200

250

300

350

400

1700 1750 1800 1850 1900 1950 2000

CO

2 Concentr

ation (

PP

M)

Year

YOU ARE HERE!

Current value 389 ppm

variation in the last 400,000 years


So what makes CO2 so important?CO2 is a greenhouse gas

And what is a greenhouse gas?Well I’m so glad you asked!



The Earth’s atmosphere keeps heat in like a green house.

To understand how a green house works we need to take a step back and look at the light energy that keeps us all alive……….




We use the wave model to help us explain light. Different colours are produced by different wavelengths of light.


Not all the light that comes from the sun is in the visible spectrum.


How hot does an object get hot when placed in front of a fire?





Light from the Sun

Light reflected from EarthAverage Value

100 watts per square metre

Light from the SunAverage Value

340 watts per square metre


Without an atmosphere what would be the average surface temperature?

-18 °C

Average Value 240 watts per square metre

Average Value240 watts

per square metre




Light from the sun heats the Earth

Light from the Sun

Earth

The Earth then radiates heat away…



The Earth’s surface temperature is determined by energy in and energy out

Heat input from the Sun

Heat lost from the Earth by radiation



The energy in and the energy out determines the Earth’s temperature. So why is the Earth warmer than -18oC

Energy gets trapped in our atmosphere and starts to heat the surface up



• The Atmosphere consists of

Illustration of atmospheric composition

About 100 molecules

O2

Ar

N2

Illustration of atmospheric composition About 1200 molecules

Water(H2O)

Increase in CO2 concentration Concentration in 19th century

Carbon dioxide (CO2)

Added in 20th Century

About 10000 molecules



What would happen if we only had Nitrogen N2 and O2 (which represents 99%) in our atmosphere?

With an atmosphere of only Nitrogen & Oxygen, what would be the surface temperature?

-18 °C

Average Value 240 watts per square metre

Average Value240 watts

per square metre


-18 °C

Average Surface

Temperature

33 °CGreenhouse

EffectTemperature for

atmosphere of O2 and N2

+15 °C




Although they make-up less than 1% of our atmosphere the green house gases of water, H2O and carbon dioxide CO2 are able to contribute 33oC to our surface temperature.

So how can these gases have such an effect??



Lets look at these gases as a chemist would..Hydrogen, H2 Oxygen, O2

Greenhouse gasses:

Water H2O

Carbon Dioxide CO2



What is special about H2O and CO2?

• Their molecules have three atoms• Their natural frequencies of vibration are in the

infra-red



It is this difference which has a huge effect on how they absorb and reflect light energy.

Nitrogen, N2 and Oxygen, O2 are able to absorb high spectrum light energy like UV. They protect us from these harmful rays, but they allow visible and infrared through

Greenhouse gases like Water, H2O and Carbon Dioxide CO2 are able to absorb lower spectrum light energy like infrared.

Infra RedUltra Violet Visible

What determines the Earth’s surface temperature?

Greenhouse Warming

33 °C

Others <1 °C

CO2 2 °C

H2O 31 °C



So greenhouse gasses drive our planet warming which is good because we’d all be pretty cold at -18oC.

But our 15oC average depends on our greenhouse gases level remaining constant, that is our energy in and energy out stabalises

• In balance at + 15 °C…On Average

240 W/m2

On Average 240 W/m2

150 W/m2

sent back to Earth

Average Value240 W/m2


On Average 280 W/m2

On Average 320 W/m2

On Average 390 W/m2

Light energysent back to Earth

Light Energysent back to Earth

Light Energysent back to Earth

On Average less than 240 W/m2



The Earth’s surface temperature is determined by energy in and energy out which in turn is determined by the greenhouse effect

Heat input from the Sun

Heat lost from the Earth by radiation



0

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400

1700 1750 1800 1850 1900 1950 2000

CO

2 Concentr

ation (

PP

M)

Year

variation in the last 400,000 years

YOU ARE HERE!

Current value 389 ppm



CO2 is a particular problem because it hangs around, unlike water that cools in the atmosphere and then precipitates as rain and snow.



CO2 does get used up by green plants but the amount we are pumping in is more that the amount used.

300

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1960 1970 1980 1990 2000 2010

CO

2 (p

pm

)

Year



CO2 does get absorbed into the oceans but this makes them more acidic which has implications for marine life.



Looking to the future….Scientists use mathematical models of the climate to

try to work out where this might lead. These models are extremely complicated as small

changes have flow on effects.We test the accuracy of these models by applying them

to the past and seeing if they will give results that match known data.



But what about reports that say the average temperature has dropped since 2000…..

-1

-0.8

-0.6

-0.4

-0.2

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0.8

1

1850 1870 1890 1910 1930 1950 1970 1990 2010

Year

Tem

pera

ture

Ano

mal

y (C

elsi

us)

Observed Temperature changes

http://www.cru.uea.ac.uk/cru/climon/data/themi/g17.dat

But its not just average temperature that matters



What happens if the model can’t keep up with reality….



“ It is a matter of social justice. If we care about injustice and inequality, we must care about climate change. Climate change exacerbates existing inequalities.”

Barbara Stocking — Chief Executive, Oxfam GB, Oxford, England



The human cost.....

Images: Human Impact Report Climate Change, Global Humanitarian Forum ,2009Words: Kofi A. Annan, President of the Global Humanitarian Forum



What can you do?Join a network:http://www.envict.org.au/http://www.350.org/Join an action:http://www.newscientist.com/embedded/mg20327271900-better-world-global-green-atlas

Express you concern• Find your federal members:

http://www.aph.gov.au/• Find your state members:

http://www.parliament.vic.gov.au/default.htm



Thanks for Listening

Science Teachers for Climate Awareness

Jane [email protected]

the science of climate change

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