The Greenhouse Effect&

Global Warming

Lecture 14: Atmospheres

Section 1: Measurements of the Temperature and CO2

in the Earth’s atmosphere.

Global Temperature: Past 130 years

Average Temperatureduring the 20th Century

The Greenhouse Effect: Trapping IR Thermal Emission

from the planet

• What is the greenhouse effect?• What is the cold evidence for Global Warming?• What different types of data indicate Global Warming• Is it good, bad, or both . . .• How would planets be different without the

greenhouse effect?• Compare the greenhouse effect on Venus, Earth, and Mars.

Questions:

Planet Earth: 4 Billion years of a stable environment

Charles Keeling

1958Mauna Loa,Hawaii

Develops techniquefor measuringcarbon dioxide inthe atmosphere.

A reduction in carbon dioxide occurs every spring and summer each year as plant growth increased in the land-rich northern hemisphere, consuming CO2 by photosynthesis..

Arctic Ice:Storing CO2 for 400,000 Years

The Vostok ice cores provide the longest continuous record of Antarctic climatic history. Cores go to a depth of 3350 meters, representing approximately 440,000 years of climate history.

Vostok ice core drilling site in Antarctica

Snow falls year after year, forming stratified layers in ice. Trapped within these layers are small air bubbles that get trapped during snow falls. These air bubbles contain samples of atmospheric composition.

Cutting an ice coreto analyze the CO2 trapped inside.

CO2 in atmosphere, measured in thick arctic ice.

CO2 Since the Year 1000 AD

FAQ 2.1, Figure 1

Ice Cores:Deuterium and 18Oxygen isotopes

Correlate with Air Temperature

Frac

tiona

l Inc

reas

e in

Deu

teriu

m

Temperature (oC)

Change

In

18O

Variations of deuterium (δD) in antarctic ice, which is a proxy for local temperature, and the atmospheric concentrations of the greenhouse gas carbon dioxide (CO2). Note the correlation.

Temperature and CO2 concentration in the atmopshereDuring the past 400,000 years (from the Antarctic Ice cores)

CO2

(ppm)

TEMP(oC)

Earth’s Temperature Increased 0.9 C in the Atmosphere and Ocean since 1880.

Figure TS.6

Patterns of linear global temperature trends over the period 1979 to 2005 estimated at the surface (left), and for the troposphere from satellite records (right). Grey indicates areas with incomplete data. (Bottom) Annual global mean temperatures (black dots) with linear fits to the data. The left hand axis shows temperature anomalies relative to the 1961 to 1990 average and the right hand axis shows estimated actual temperatures, both in °C. Linear trends are shown for the last 25 (yellow), 50 (orange), 100 (magenta) and 150 years (red). The smooth blue curve shows decadal variations (see Appendix 3.A), with the decadal 90% error range shown as a pale blue band about that line. The total temperature increase from the period 1850 to 1899 to the period 2001 to 2005 is 0.76°C ± 0.19°C.

Global Averaged Temperature

Change in Temperature from 1960 to 2000

Since 1850: Atmospheric CO2 has increased by 25%

Increase in Temperature tracksIncrease in Greenhouse Gases

Year1850 2000

Temperature vs Time

Earth Data: CO2 and Temperature

Carbon Dioxide:Humans are putting CO2

into our AtmosphereWorldwide CO2 ProductionBy fuel type: 1970 - 2020 Burning coal

Gasoline

Natural gas

Fact, not speculation.

The Greenhouse Effect&

Global Warming

Lecture 13: Atmospheres

Section 3: Glaciers are Retreating Feedback Mechanisms of the Greenhouse Effect Projections for the Future of our Atmosphere

Franz Josef Glacier In Retreat1951

1960

1964

1939

Muir Glacier, Alaska1941

2004

McCarty Glacier - Alaska

Retreat of Glaciers

1948 2002

Trift Glacier, Gadmental, Berner, Oberland Switzerland

2006

Mt. Hood, Oregon

1984 2002

A 2003 photograph of the ~2.9 square kilometer Easton Glacier on Mount Baker in Washington State. Between ~1890 and 1950, this glacier retreated ~2400 meters. It subsequently expanded 600 meters during a locally cold period between 1950 and 1979. Since then, it has again retreated 315 meters (as of 2002) with 150 meters lost solely between 1997 and 2002.[1]. The extent of the glacier in 1985 is indicated in the figure.

Easton Glacier

All survey regions except Scandinavia show a net thinning. This widespread glacier retreat is generally regarded as a sign of global warming. During this period, 83% of surveyed glaciers showed thinning with an average loss across all glaciers of 0.31 m/yr.

Retreating Glaciers

Glacier Mass

The Greenhouse Effect&

Global Warming

Lecture 13: Atmospheres

Section 2:The Physics of Infrared Absorption by Molecules

Earth Data: CO2 and Temperature

Why is Temperature closely related to CO2 ?

Vibrational Modes for CO2

C OO

CO O

O OC

n1 symmetric

n2 bending absorb 15 mm

n asymmetric absorb 4.3 mm

Greenhouse effect caused by CO2: CO2 molecules absorb infrared light at specific wavelengths, trapping that energy in the Earth’s atmosphere.

Other Greenhouse Gases

O

O O

O

H H

water ozone

N NO C

H

H

H H

methanenitrous oxide

These molecules in Earth’s atmosphere absorb IR light

Absorption in the Earth's atmosphere (middle panel) and the effect that this has on both solar radiation and upgoing thermal radiation (top panel). Individual absorption spectrum for major greenhouse gases plus Rayleigh scattering are shown in the lower panel.

Both the Earth and the Sun shine by thermal emission of light. For the sun, these emissions peak in the visible region and correspond to a temperature of ~5500 K. Emissions from the Earth vary following variations in temperature across different locations and altitudes, but always peak in the infrared. The Earth has an average emission temperature of about 250 K (-20 C).

The wavelengths of absorption bands are determined by the chemical properties of the gases present. Water vapor is the most significant of these greenhouse gases, followed by carbon dioxide.

Per

cent

Abs

orpt

ion

Light Absorbed by the Atmosphere

Absorption by gases In the Earth’s Atmosphere

Absorption by different molecules l = 0-15 µm

Absorption

Transmission

Peak thermal emission at T=300K

CO2

BendingMode

How Greenhouse Gases Warm the Troposphere

CO2

The Greenhouse Effect Visible Sunlight passes through a

planet’s atmosphere. Some of this light is absorbed by the

planet’s surface. Planet warms. Emits its own light:

“thermal radiation”, as infrared (IR) light - back out to space.

IR light is absorbed by the molecules and sent back to Earth !

Result: the temperature is higher than if there were no atmosphere at all.

What Determines a Planet’s Surface Temperature?

Greenhouse Effect cannot change incoming Sunlight, so it cannot change the total energy returned to space.• it increases the energy (heat) trapped in lower atmosphere• it works like a blanket

In the absence of the Greenhouse Effect, what would determine a planet’s surface temperature?• the planet's distance from the Sun• the planet’s overall reflectivity, “albedo” (fraction reflected)• the higher the albedo, the less light absorbed, planet cooler

Earth’s average temperature would be –17º C (–1º F) without the Greenhouse Effect !

DataCO2 Levels are higher than in the past 400,000 years.

Temperature rose 0.9 C since 1860.

CO2 correlates with Temperature for 400,000 years.

Data: CO2 and Temp. are Rising.

Physics: Temp. Related to CO2, by the Greenhouse Effect.

Global Warming Dataand Physics.

Feedback: Declining Arctic IceCauses less reflectivity (Albedo)

Is the Sun to Blame ? No. Luminosity has been constant.

Sunlight hitting Earth:

• 11 year Sunspot cycle• Offsets among instruments• No trend

Percentage change in monthly values of the total solar irradiance composites of Willson and Mordvinov (2003; WM2003, violet symbols and line) and Fröhlich and Lean (2004; FL2004, green solid line).

(Solar max)

Global Warming Made a political issue by certain people.

Three Facts are Absolute:

1. Earth has warmed by 0.5 C in past 50 years. Temperature rise greatest in past 10 years.

2. Humans are increasing by 30-50% the CO2 in the atmosphere.3. Rising CO2 will cause rising temperatures

Only Question: Not Whether, but by how much are humans contributing to Global Warming ?

Feedback Proceses:Positive and Negative

Suppose Temp rises ==> Evaporation of ocean water.

Feedback: H2O is a greenhouse gas ==> Earth gets even Warmer !

But clouds may form, increasing albedo.==> Earth cools.

The Arctic:Positive Feedback Process

Temp rise causes polar cap ice to melt. Artic ground exposed: dirt absorbs more

sunlight (lower albedo). Ground warms up more: Earth gets hotter. More polar cap ice melts. Earth gets even

hotter.

Consequences ofGlobal Warming

1. More evaporation of oceans: More storms, and more severe storms.

2. Water in oceans expand with rising Temp. Sea level has already risen 20 cm in past 100 years. Coastal regions and islands flood.

3. Polar caps and Glaciers melt: Causes rising ocean levels.

4. Change in ocean current patterns. Desserts may get rain; Farmland may get none.

Consequences ofGlobal Warming

According to the UN report: The world will be a much hotter place by 2100.

Coral reefs almost extinctIn North America, a new dust-bowl brings deserts to life in the high plains states, centered on Nebraska, but also wipes out agriculture andcattle ranching as sand dunes appear across five US states, from Texas in the south to Montana in the north.Rising sea levels accelerate as the Greenland ice sheet tips into irreversible melt, submerging atoll nations and low-lying deltas. In Peru, disappearing Andean glaciers mean 10 million people face water shortages. Warming seas wipe out the Great Barrier Reef and make coral reefs virtually extinct throughout the tropics. Worldwide, a third of all species on the planet face extinction+3.4 ｡ :

Rainforest turns to desertThe Amazonian rainforest burns in a firestorm of catastrophic ferocity, covering South America with ash and smoke. Once the smoke clears, the interior of Brazil has become desert, and huge amounts of extra carbon have entered the atmosphere, further boosting global warming. The entire Arctic ice-cap disappears in the summer months, leaving the North Pole ice-free for the first time in 3 million years. Polar bears, walruses and ringed seals all go extinct. Water supplies run short in California as the Sierra Nevada snowpack melts away. Tens of millions are displaced as the Kalahari desert expands across southern Africa.

Melting ice caps displace millionsRapidly-rising temperatures in the Arctic put Siberian permafrost in the melt zone, releasing vast quantities of methane and CO2. Global temperatures keep on rising rapidly in consequence. Melting ice-caps and sea level rises displace more than 100 million people, particularly in Bangladesh, the Nile Delta and Shanghai. Heatwaves and drought make much of the sub-tropics uninhabitable: large-scale migration even takes place within Europe, where deserts are growing in southern Spain, Italy and Greece. More than half of wild species are wiped out, in the worst mass extinction since the end of the dinosaurs. Agriculture collapses in Australia+5.4 ｡ : Sea levels rise by five metresThe West Antarctic ice sheet breaks up, eventually adding another five metres to global sea levels. If these temperatures are sustained, the entire planet will become ice-free, and sea

Predictions of temperatures next 100 years

DEPENDS ON MAGNITUDE OF FEEDBACK AND RATE OF INCREASE OF GHG. IN 100 YEARS, FORCED CLIMATE CHANGE WILL MOST LIKELY EXCEED NATURAL VARIABILITY

The Greenhouse Effect&

Global Warming

Lecture 13: Atmospheres

Section 4: Comparison of Atmospheres: Earth to Venus and Mars

4.6 Billion Years Ago ...

(150 million km from Sun)

1 AU0.7 AU 1.5 AU

SUNVenus Earth Mars

Temperature: Top of Atmosphere

Tem

pera

ture

(Cel

siu)

500

300

100 0

-100-100

0

100

200

300

400

500

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

decreases with distance from Sun

5500 oC

Earth-18oC (0oF)

Venus

Distance From SunMars

0

0

300

500

200

100

-100

400

Tem

pera

ture

(C

)

Clue: atm composition

-100

0

100

200

300

400

500

0.5 1 1.5 2

500

300

100

0

-100

Tem

pera

ture

(Cel

sius

)

EARTH:Surface 15oC (60oF)Top of Atm: -18oC (0oF)

All three phases of water

Surface warmer than top of atm Greenhouse Effect

Surface

No Greenhouse

Climate History of Venus Venus should have outgassed as much H2O as Earth.

• Early on, when the Sun was dimmer, Venus may have had oceans of water Venus’ proximity to the Sun caused all H2O to evaporate.

• H2O caused runaway greenhouse effect • surface heated to extreme temperature• CO2 released from rocks: Adds to greenhouse effect• UV photons from Sun dissociate H2O; H2 escapes, O is stripped

If Earth moved to Venus’ Orbit

Venusian Weather Today• Venus has no seasons to speak of.

• rotation axis is nearly 90º to the ecliptic plane• Venus has little wind at its surface

• rotates very slowly, so there is no Coriolis effect• The surface temperature stays constant all over Venus.

• thick atmosphere distributes heat via two large circulation cells There is no rain on the surface.

• it is too hot and Venus has almost no H2O Venusian clouds contain sulfuric acid!

• implies recent volcanic outgassing?

Mars’ Thin Atmosphere

Martian sunset illustrates just how thin the Martian atmosphere is.

The Earth is Changing Rapidly

Who Speaks for Earth?

Who is the steward, theshepherd, the parentof our home planet?

CO2 is higher than at any time in recorded history. Global Temperatures are rising

Humans are changing the planet Earth, for the first time in history.

We don’t know the outcome of our experiment with our planet. Maybe everything will be perfectly OK. But Venus offers pause.

Suggested Movie:

An Inconvenient Truth

Show: An Inconvenient Truth

Get DVD. Interesting Chapters: 5-7-9, 11, 16, 20, 21-28, 30-32(or 5-9, 16-28)Takes 30 min.

Martian Weather: N Polar Ice Cap & Dust Storm

Martian Weather Today• Seasons on Mars are more extreme than on Earth

• Mars’ orbit is more elliptical• CO2 condenses & vaporizes at opposite poles

• changes in atmospheric pressure drive pole-to-pole winds• sometimes cause huge dust storms