Protons for Breakfast Week 4: Global Warming

In the event of an alarm sounding…

Global Warming Can we collect your facts please…

How it all fits together… Electromagnetic waves Atoms Heat Electricity

How it all fits together…

Global Warming The problem with this problem…

This evening… Do you have any personal evidence that the climate is changing? What do we mean by ‘climate?’

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.

This evening… Why is the Earth the temperature it is? The Earth’s Atmosphere Carbon dioxide Why are scientists concerned? What’s going to happen? What should we do? –We’d like you to do this!

The Simple Story What determines the surface temperature of the Earth? Energy Balance

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

What determines the surface temperature of the Earth? Simple Story (1) Light from the Sun heats the Earth… The Sun Earth 6400 °C

What determines the surface temperature of the Earth? Simple Story (2) Drawn to Scale… The Sun Earth (drawn 100 times too big) (drawn to scale)

What determines the surface temperature of the Earth? Simple Story (3) Light from the Sun heats the Earth… The Earth then radiates heat away… Light from the Sun Earth

What determines the surface temperature of the Earth? Simple Story (4) 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

What determines the surface temperature of the Earth? The Energy Balance of the Earth

Earth Warms Earth Cools What determines the surface temperature of the Earth? The Numbers World Energy Production heat input from the Sun heat lost from the Earth CO2 emissions

What determines the surface temperature of the Earth? Some more details…

What determines the surface temperature of the Earth? More detail (1) We need to know: How much light reaches the Earth? How much light reaches the Earth’s Surface? How much energy is radiated from the Earth’s Surface?

What determines the surface temperature of the Earth? How much light reaches the Earth? Light from the Sun heats the Earth… Earth At the top of the atmosphere Above the Equator At midday About 1360 W/m 2

What determines the surface temperature of the Earth? How much light reaches the Earth? Light from the Sun heats the Earth… Earth North Pole South Pole Equator 1360 W/m Whole Earth Average 340 W/m 2

What determines the surface temperature of the Earth? More detail (1) Light reflected from Earth Average Value 100 watts per square metre Light from the Sun Average Value 340 watts per square metre

What determines the surface temperature of the Earth? 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

What determines the surface temperature of the Earth? 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!

1. What determines the surface temperature of the Earth? More detail (2) Infra Red Radiation cools the Earth… Light from the Sun heats the Earth…

1. What determines the surface temperature of the Earth? More detail (2) Light from the Sun heats the Earth… Average Value 240 watts per square metre Average Value 240 watts per square metre

1. What determines the surface temperature of the Earth? More detail (2) How hot must the Earth be to radiate 240 W/m 2 ? Average Value 240 watts per square 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

A Question and an Answer 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

1. What determines the surface temperature of the Earth? More detail (4) -18 °C Average Surface Temperature 33 °C Temperature for radiation balance +15 °C Greenhouse Effect

What determines the surface temperature of the Earth? The Earth’s surface is 33 °C warmer than it would be if had no atmosphere

The Atmosphere Earth’s Atmosphere the Greenhouse Effect

The Atmosphere More detail (5) What is the composition of the atmosphere? Gas% Nitrogen (N 2 )78.1 Oxygen (O 2 )20.1 Argon (Ar)0.93 Water (H 2 O)0.1 to 1 Carbon Dioxide (CO 2 )0.035

Illustration of atmospheric composition More detail (6) About 100 molecules O2O2 Ar N2N2

Illustration of atmospheric composition More detail (7) About 1200 molecules Water(H 2 O)

Illustration of atmospheric composition More detail (8) About molecules Carbon dioxide (CO 2 )

The Atmosphere More detail (9) Nitrogen (N 2 ), Oxygen (O 2 ) & Argon (Ar) > 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

The Atmosphere More detail (10) With an atmosphere of only Nitrogen Oxygen & Argon, what would be the surface temperature? Average Value 240 watts per square metre Average Value 240 watts per square metre -18 °C

The Atmosphere More detail (10) Greenhouse warming is caused by Water (H 2 O) Carbon Dioxide (CO 2 )

The Atmosphere More detail (11) What is special about H 2 O and CO 2 ? Molecules have three atoms Natural frequencies of vibration in the infra-red They make the atmosphere opaque to certain infra-red frequencies

The Atmosphere More detail (12) Absorbtion frequencies determined by exact frequencies of molecular jiggling

The Atmosphere and the Greenhouse Effect The Transparency of the Atmosphere

Warning! Complicated diagram !

Infra RedUltra VioletVisible Absorption bands SUN 6400 °C (left-hand scale)

Infra RedUltra VioletVisible Water Absorption bands SUN 6400 °C (left-hand scale) HEATER 1000 °C

1. What determines the surface temperature of the Earth? More detail (2) Infra Red Radiation cools the Earth…

What determines the surface temperature of the Earth? More detail (16) In balance at + 15 °C… On Average 240 W/m 2 On Average 390 W/m W/m 2 sent back to Earth Average Value 240 W/m 2

Greenhouse Warming 33 °C Others <1 °C CO 2 2 °C H 2 O 31 °C If H 2 O is a more important greenhouse gas than CO 2, why aren’t we worried about water vapour emissions? A Question

Answer Residence time Excess H 2 O in the atmosphere causes rain within a few days Excess CO 2 in the atmosphere takes a few hundred years to remove Photo Credit

How the parts fit together Atmospheric Water Global Temperature Greenhouse Effect Evaporation Small slowly changing contribution to Greenhouse Effect Clouds Carbon Dioxide

Experiment 1 Does water block infrared light?

Infra RedUltra VioletVisible Water Absorption bands SUN 6400 °C (left-hand scale) HEATER 1000 °C

Experiment 2 Does CO 2 absorb infrared light more than air?

Infra RedUltra VioletVisible Water Absorption bands SUN 6400 °C (left-hand scale) HEATER 1000 °C

Greenhouse Effect Earth’s surface is warmed by the Greenhouse Effect Caused by water and carbon dioxide Turns the Earth from a ‘snowball’ with a hot Equator into the relatively temperate place So what’s the problem?

Carbon dioxide & the carbon cycle The amount of carbon dioxide in the Earth’s atmosphere is increasing…

Atmospheric CO 2 Concentration versus year Historical Value 280 ppm Current value 388 ppm parts per million

Atmospheric CO 2 Concentration versus year (Detail 2) Click Graph to link to NOAA Web Site for Latest Data

Carbon dioxide Why is the amount of carbon dioxide in the Earth’s atmosphere is increasing? We are digging up geological deposits of carbon –Coal & Oil & Gas We are burning them! C+ O 2 →CO 2

Michael’s family CO 2 emissions 0.2 kg per mile 4000 miles per year 800 kg CO 2 /year 0.3 kg per mile per person 1000 miles per year 600 kg CO 2 /year 0.5 kg per kWh 7300 kWh per year 3650 kg CO 2 /year Holiday in California! person miles! 16,000 kg CO 2 /year 0.2 kg per kWh kWh per year 3400 kg CO 2 /year

My family’s CO 2 emissions 8500 kg of CO 2 per year at home kg For our holiday in California! 24.5 tonnes!! There are many families like Michael’s…

Global CO 2 Emissions 30 billion tonnes CO 2 8 billion tonnes C EVERY YEAR

Question Is 8 billion tonnes of carbon per year (emitted as CO 2 ) a lot or a little?

Carbon Cycle (Amounts of carbon in billions of tons) ,000 39, ,000 3, increasing at 3.2/year 60

Cause for Concern? What is the effect of increased levels of carbon dioxide in the Earth’s atmosphere? Nobody knows

Climate Models What is the current effect of CO 2 A net extra ‘forcing’ of around 2 watts per square metre… Average 240 W/m 2 On Average 390 W/m W/m 2 Average 240 W/m W/m 2

An additional 2 watts per square metre of ‘radiative forcing’ Scientific American March 2004

Cause for Concern? Should we be concerned?

Cause for Concern? Scientists are concerned for several reasons: 1.Pre-historic studies show a correlation between atmospheric CO 2 levels and global climate 2.There are observed changes in climate

Cause for Concern? Prehistoric Studies 1 year of snow From approximately 16,250 years ago

Pre-Historic studies Bubbles in Arctic and Antarctic Ice 300 ppm Maximum180 ppm Minimum Ice Ages

Milankovitch Cycles Did CO 2 cause the ice ages? No, CO 2 helped us escape from them! Ice ages are caused by small changes in the orbit of Earth around the Sun Milankovitch Cycles

The Earth Orbits the Sun Daily Rotation Northern Hemisphere Summer Northern Hemisphere Winter Angle varies from 22.5º to 24.5º And back again every 40,000 years 23.5º tilt Earth Spins times on its journey around the Sun

Most Southerly Advance Mid Winter Seasonal Changes in Ice Cover

Most Southerly Advance Mid Winter Most Northerly Retreat Mid Summer If summer day length increases by a minute or two or days are warmer on average by a small amount This area used to reflect 90% of sunlight Now it reflects only around 30% Warmer ground emits trapped CO 2 and Methane

Pre-Historic studies Bubbles in Arctic and Antarctic Ice Range of variation in last 800,000 years Current value 388 ppm

Cause for Concern? Observed Changes in Climate

Observed Changes Average surface temperature is difficult to measure

Observed changes It is difficult to detect small changes in a long series of data?

My Weight: Spotting a trend

Observed changes Best estimates But its not just average temperature that matters

Other observations Germany

Other observations Muir Glacier, Alaska Photo credit: Global Warming Art

Other observations Argentina

Causes for concern Pre-historic climate studies Observed changes

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 likely2007: It is very likely

Climate Models Predictions Try to ‘add up’ the many factors affecting climate? Climate Models help us estimate… ‘What’s going to happen?”

The Future… CO 2 levels will continue to rise. If we make a 50% cut in global emissions –Requires a much greater cut (80% ?) by the UK Then CO 2 will stabilise at twice historical levels

IPCC Predictions… Human CO 2 emissions

IPCC Predictions… Atmospheric CO 2 concentration

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

What could we do? What should we do? Nothing –Spend money on coping with consequences We could reduce the amount of CO 2 we emit –Even though this involves saving energy, this still costs money –Things we do now will cost us money now Is global warming our top priority? –Global poverty? AIDS? –Hospitals? Education? Science? Banks? Would you vote to increase the price of all fuels?

So… What do YOU think we should do?

Despair? You may never know what results come of your action, but if you do nothing, there will be no result. Mahatma Ghandi

See you next week to discuss… Mobile Phone Safety! Goodnight

Unused Slides

Contributions to Climate Forcing Greenhouse gases Carbon Dioxide Methane Chlorofluorocarbons Nitrous Oxide Ozone Aerosols Black Carbon Reflective aerosols Cloud droplet changes Land cover changes Sun Climate Forcing (W/m 2 ) 0+1

Feedback Global Temperature More Evaporation Climate Forcing Increased Climate Forcing Increased Water Vapour Increased Cloud Cover Decreased Climate Forcing Negative Positive

Powers of Ten (Global Warming) Length scale in metres Very Very Small Very Very Large Human Relationships Diameter of the Earth Distance to the Sun Tallest Mountain Deepest Trench Atoms & Molecules Microbes The phenomenon of global warming involves physical processes with length scales spanning 20 powers of 10!

The spectrum of sunlight

Global CO 2 Emissions ?

IPCC Predictions… Climate Research Unit East Anglia University metres in 100 years ? 1 metre

IPCC Predictions… 1 metre in 100 years

UK CO 2 Emissions

Daily Rotation Northern Hemisphere Summer Northern Hemisphere Spring Equinox Northern Hemisphere Winter Northern Hemisphere Autumn Equinox Angle varies from 22.5º to 24.5º And back again every 40,000 years 23.5º tilt Earth Spins times on its journey around the Sun

Carbon dioxide The amount of carbon dioxide in the Earth’s atmosphere is increasing… Historically280 ppm ppm ppm 2025about 425 ppm ppm

Cause for Concern? Climate models

Climate Models What is a computer model of the climate? © Australian Bureau of Meteorology

Climate Models What is the output of a climate model?