Global warming

Protons for Breakfast

Global Warming

Week 4

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1800 1850 1900 1950 2000

In the event of…In the event of an attack of mutant bananas…

Global Warming

Can we collect your facts please…

What do we mean by Climate?

What is the Climate?

It’s the average weather

in a particular area

What is the Climate?

It’s the average weather

Over a period a time (30 years usually)

Averages of temperatures and rain occurrence

Calculated scientifically

Things like that determine what we call the Climate

Determine what the climate of a place will be.

One problem…

Do you have any personal evidence

that the global climate is changing?

This Evening…

1. Why is the Earth’s surface the temperature it is?

2. The Earth’s Atmosphere

3. Increasing Carbon Dioxide

4. Should we be concerned?

5. What’s going to happen?

6. What should we do?

Energy Balance

How hot does an object get when

placed in front of a fire?

Light from the Sun heats the Earth…

The Sun

Earth

5400

°C


Drawn to Scale…

The Sun Earth

(drawn 100 times

too big)

(drawn to scale)


The Earth then radiates heat away…

Light from

the Sun

Earth

Energy Balance

heat input from the Sun

heat lost from the Earth by

radiation

When there is balance, the Earth’s average

temperature will be stable

Earth

Warms

Earth

Cools

The Energy Balance of the Earth

Earth

Warms

Earth

Cools

Energy Balance: to scale

World Energy

Production

heat input from the

Sun

heat lost from the

Earth

Some more details…

How much light reaches the Earth?

Earth•At the top of the atmosphere

•Above the Equator

•At midday

•About 1360 W/m2

How much light reaches the Earth?

EarthNorth Pole

South Pole

Equator

1360 W/m2

680

Whole Earth Average 340 W/m2

How much light reaches the Earth’s Surface

Light reflected from Earth

Average Value

100 watts per square metre

Light from the SunAverage Value

340 watts per square metre

Hold on a moment!

What about all the

heat rising up

from the Earth’s hot

centre?

Earth

6400 km radius

5500 °C

Heat flow is less than

0.1 Watt per square

metre

Temperature increases by ~20 °C

for each kilometre below the

Earth’s surface

Heat flow to and from

surface from the Sun

240 Watt per Square

metre

A remarkable fact…

Heat flow from the centre of the Earth

can be completely ignored when

considering what determines the

surface temperature of the Earth!

What determines the surface

temperature of the Earth?

Infra Red Radiation cools the Earth…


Radiation Balance


Average Value

240 watts per square

metre

Average Value

240 watts

per square metre

Radiation Balance

How hot must the Earth be to radiate 240 W/m2 ?

Average Value


metre

-18 °C

A Question

What is the average temperature of the Earth?

1 metre above the surface and averaged over:• day and night, • all latitudes and longitudes.• all seasons

(a) – 15 ° C(b) – 5 ° C(c) + 5 ° C(d) + 15 °C

Summary

-18 °C

Average

Surface

Temperature

33

°CTemperature

for radiation

balance

+15 °CGreenhouse

Effect

The Earth’s surface is 33 °C warmer

than it would be if had no atmosphere

This Evening…







The composition of the atmosphere?

Gas %

Nitrogen (N2) 78.1

Oxygen (O2) 20.1

Argon (Ar) 0.93

Water (H2O) 0.1 to 1

Carbon Dioxide (CO2) 0.035

Illustration of atmospheric composition

About 100 molecules

O2

Ar

N2


About 1200 molecules

Water(H2O)


About 10000 molecules

Carbon dioxide (CO2)

Nitrogen (N2), Oxygen (O2) & Argon (Ar)

Suppose the atmosphere contained no carbon dioxide or water

• N2, O2 and Ar is more than 99% of the atmosphere

• Molecules have one or two atoms

• Natural frequency of vibration in the ultra-violet

• Make atmosphere opaque to ultra-violet light

• Transparent to infra-red and visible radiation

Nitrogen (N2), Oxygen (O2) & Argon (Ar)

With an atmosphere of only

Nitrogen Oxygen & Argon,

what would be the surface temperature?

Average Value


metre

Average Value

240 watts

per square metre

-18 °C

Greenhouse warming is caused by

Water (H2O)

Carbon Dioxide (CO2)

What is special about H2O and CO2

• Molecules have three atoms

• Natural frequencies of vibration in the infra-red

• They make the atmosphere opaque to certain infra-red frequencies

Vibrations of CO2 and H20

• Different types of molecular jiggling occur at different frequencies

Water H20 Carbon dioxide C02

Absorption demo

Frequency

The Transparency of the Atmosphere

Warning!

Complicated diagram

!

Infra RedUltra Violet Visible

Absorption bands

Infra Red Radiation cools the Earth…

Radiation Balance in the 20th Century…

On Average

240 W/m2

On Average

390 W/m2

150 W/m2

sent back to

Earth

Average Value

240 W/m2

On Average

+ 15 ºC

Greenhouse Warming

33

°C

Others <1 °C

CO2 2 °C

H2O 31

°C

If H2O is a

more important

greenhouse gas

than CO2,

why aren’t we

worried about

water vapour

emissions?

Residence time

Because excess H2O in

the atmosphere

• causes rain within a

few days

Excess CO2 in the

atmosphere

• takes a few hundred

years to remove

Photo Credit

http://www.cepolina.com

If H2O is a more important

greenhouse gas than CO2, why

aren’t we worried about

water vapour emissions?

How the parts fit together

Atmospheric

Water

Global

Temperature

Greenhouse Effect

Evaporation

Small slowly changing

contribution to

Greenhouse Effect

Clouds

Carbon

Dioxide

Experiment

Does water block infrared light?

A Children’s song What does the glass of a Greenhouse do?

It lets the short solar rays pass through

The objects in the house absorb these rays

And re-radiate them as long heat rays

What does the glass of a Greenhouse do?

It doesn’t let the long heat rays pass through

Trapped by the glass they bounce back and forth,

Re-radiated and re-absorbed

Stay Stay, you long heat rays, Warm up the house on cold cold days

Stay Stay, you long heat rays, Warm up the house on coooooold cold days

The atmosphere is like a greenhouse too

It lets most of the solar rays through

The surface of the Earth absorbs these rays

And re-radiates them as long heat rays

There’s vapour in the air, What does it do?

It doesn’t let the long heat rays pass through

Trapped by the vapour they bounce back and forth,

Re-radiated and re-absorbed

Stay Stay, you long heat rays, Warm up the house on cold cold days

Stay Stay, you long heat rays, Warm up the Earth on cooooooold cold days

Greenhouse Effect

• Earth’s surface is warmed by the Greenhouse Effect

• Caused by:

Water (mainly)

and carbon dioxide

• Turns the Earth from a ‘snowball’ with a hot Equator into the relatively temperate place

So what’s the problem?

This Evening…







0

50

100

150

200

250

300

350

400

1700 1750 1800 1850 1900 1950 2000

CO

2 C

on

ce

ntr

ati

on

(P

PM

)

Year

Atmospheric CO2 Concentration

versus year

Historical Value

280 ppm

Current value

~390 ppm

parts per

million

Click for

latest value

http://www.esrl.noaa.gov/gmd/ccgg/trends/



Carbon dioxide

Why is the amount of carbon dioxide in

the Earth’s atmosphere is increasing?

• We are digging up carbon as:

Coal & Oil & Gas

• We are burning them!

C + O2 →CO2

Michael’s family

CO2 emissions

0.2 kg per mile

4000

miles per year

800 kg CO2/year

0.3 kg per

mile per

person

1000

miles per year

600 kg

CO2/year

0.5 kg per

kWh

7300

kWh per year

3650 kg

CO2/year

Holiday in

California!

56000 person

miles!

8,000 kg

CO2/year

0.2 kg per

kWh

17000

kWh per year

3400 kg

CO2/year

My family’s CO2 emissions

8500 kg of CO2 per year at home

8000 kg For our holiday in California!

16.5 tonnes!!There are many families like Michael’s…

Carbon?

Or Carbon dioxide?

CO2

1 tonne of CO2

0.27 tonne of C 0.73 tonne of O2

Global CO2 Emissions

0.0

2.0

4.0

6.0

8.0

10.0

1750 1800 1850 1900 1950 2000

0

5

10

15

20

25

30

35

Billio

ns

of

To

nn

es

of

Ca

rbo

n

Year

Billio

ns

of T

on

ne

s o

f

Ca

rbo

n D

iox

ide

30 billion tonnes CO2

8 billion tonnes C

EVERY YEAR

Question

Is 8 billion tonnes of carbon per year

(emitted as CO2)

a lot or a little?

Carbon Cycle (Amounts of

carbon in

billions of tons)

760

908

2,000

39,000

500

1,000

3,000(Coal)

300 (Oil &Gas)

2

2

760 increasing at 4 per year

60

Cause for Concern?

What is the effect of increased levels of

carbon dioxide in the Earth’s atmosphere?

Nobody knows

Radiation ‘Balance’ in 2012…

On Average

<240 W/m2

On Average

390 W/m2

150 W/m2

sent back to

Earth

Average Value

240 W/m2

On Average

+ 15 ºC

+2 W/m2

+?? ºC

Earth

Warms

Earth

Cools

Energy Balance: to scale

heat input from the

Sun

heat lost from the

Earth

This Evening…







4. Why are scientists are concerned

1. Pre-historic studies show a strong correlation

between atmospheric CO2 levels and global

climate.

2. There are observed changes in climate

Prehistoric Studies

1 year of snow

From approximately

16,250 years ago

0

100

200

300

400

0200400600800

Ca

rbo

n D

iox

ide

Co

nc

en

tra

tio

n (

PP

M)

Thousands of years befo re present day

Bubbles in Arctic and Antarctic Ice

300 ppm Maximum

180 ppm Minimum

Ice Ages

395 ppm

Cause for Concern?

Observed Changes in Climate

A Question?One estimate of the Land Surface Temperature?

A Question?

Berkeley

NA SA G ISS

Hadley CR U

NO AA NC DC

What has happened?

What did Global Warming Theory predict in 1981?

http://berkeleyearth.org

But its not just average

temperature that matters

http://berkeleyearth.org/

GlaciersMuir Glacier, Alaska

Photo credit:

Global Warming Art

Glaciers are

retreating:

worldwide

Arctic Sea Ice http://nsidc.org/arcticseaicenews/

http://nsidc.org/arcticseaicenews/

http://nsidc.org/arcticseaicenews/

Arctic Sea Ice Minima

2012

2013

A Question

Can we be completely sure that the

climate changes we observe are caused by

anthropogenic emissions of carbon dioxide?

Man-made

and

Woman-made

2001: It is likely

2007: It is very likely

2013: It is very very likely

This Evening…







Climate Models

‘What’s going to happen?”

• Climate Models ‘add up’

the many factors

Nobody knows

The best ‘realistic’ possibility…

If we make a 50% cut in global emissions:

80% cut in the UK

CO2 concentraions will rise to

twice historical levels

and stabilise

IPCC Predictions… Global Mean Temperature

We stop all emissions NOW

We BEGIN to stop all emissions EVENTUALLY

We BEGIN to stop all emissions NOW

We do nothing

This Evening…







What should we do…

Nothing EverythingSomething

What could we do?

What should we do?

In smaller groups

• Please come up with some

questions, and suggestions

• We will gather these together and

then discuss them!

You decide!

Despair?

You may never know what results come of your action,

but if you do nothing,

there will be no result.

Mahatma Ghandi

Global warming

Education

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