AOS 171: Global Change Exam 1

Our sun's output four billion years ago was 25% weaker than at present. What could account for the planet not having been a frozen ice ball?

There was a lot more CO₂ in the atmosphere in the past meaning that more infrared radiation was trapped to heat Earth’s surface. The CO₂ levels decreased with increased photosynthesis and rock formation as the sun’s output increased.

How is the earth’s protective magnetic field generated?

This is the magnetosphere that protects the earth from energetic solar and cosmic particles. The magnetic field is formed because of the earth’s rotating, molten metallic interior. When rotated, electrons are accelerated creating the magnetic field known as the magnetosphere.

Where does ozone come from?

Upon the creation of oceans, their surface protected photosynthetic organisms from UV-Radiation. These organisms took CO₂ out of the atmosphere and replaced it with O₂ which reacted with UV radiation to form O₃ (ozone).

How did the ozone layer help life to colonize the land?

Life colonized the land surface via the positive feedback among photosynthesis, ozone, and UV protection; when life is protected by the Ozone Layer from UV radiation, they colonize the land, with plants making more oxygen, hence more ozone (positive feedback)

Where is most of the ozone layer?

Stratosphere (about 90%)

How thick is the ozone layer?

About 3 mm thick

What are the approximate relative masses of the atmosphere, hydrosphere and lithosphere?

Atmosphere: 5 x 10¹⁸ kg

Hydrosphere: 300 times larger than atmosphere

Lithosphere: 5000 times larger than atmosphere

How did the present atmosphere come into being?

The present atmosphere was outgassed, with rain, photosynthesis, and rock formation accounting for our current mixture.

Compare the gases that come out of volcanoes with the mixture of air that we breathe. How can the discrepancies be resolved?

The discrepancies (fact that there is hardly any N2 and O2 coming out of volcanos, but air is mostly made up of these two molecules and that volcanic emissions are mainly CO2 and H2O which is much greater than the concentration in the air

• Precipitation created the oceans and removed sulfuric acid (H2SO4) and carbonic acid (CaCO3), which became incorporated into rocks.

• Photosynthesis gradually created fossil fuels and oxygen, and removed the CO2

• Photodissociation (dissociation of a chemical compound by the action of light) of H2O at high altitudes, with escape of lighter H to space, probably helped add even more oxygen to get to the 21%

• N2 does not react or dissolve readily, so it simply built up over time to 78%

Describe the photosynthesis - oxidation equation in words.

𝑃ℎ𝑜𝑡𝑜𝑠𝑦𝑛𝑡ℎ𝑒𝑠𝑖𝑠:             

𝑠𝑢𝑛𝑙𝑖𝑔ℎ𝑡 + 𝐻₂𝑂 + 𝐶𝑂₂ → 𝑂₂ + ℎ𝑦𝑑𝑟𝑜𝑐𝑎𝑟𝑏𝑜𝑛𝑠                               

𝑂𝑥𝑖𝑑𝑎𝑡𝑖𝑜𝑛 (𝑐𝑜𝑚𝑏𝑢𝑠𝑡𝑖𝑜𝑛):              

 𝑒𝑛𝑒𝑟𝑔𝑦 + 𝐻₂𝑂 + 𝐶𝑂₂  ← 𝑂₂ + ℎ𝑦𝑑𝑟𝑜𝑐𝑎𝑟𝑏𝑜𝑛𝑠 (𝑓𝑜𝑠𝑠𝑖𝑙 𝑓𝑢𝑒𝑙𝑠)                                      

During the northern summer does atmospheric CO2 concentration rise or fall?

The northern hemisphere land mass dominates so during the northern summer CO₂ falls.

During northern winter, do atmospheric CO₂ concentrations rise or fall? Why?

There isn’t much photosynthesis, so CO₂ rises in the northern winter time

During the last ice age were atmospheric CO₂ and CH₄ concentrations higher or lower than at present?

They were lower than at present—last ice age was around 50,000 to 10,0000 on graph

What relationship between CH₄ and CO₂ concentrations and temperature are found in the ice core record? What might explain this relationship and what will this relationship imply for the next few centries?

High values of CH₄ and CO₂ means higher temperatures due to the positive feedback nature of GHGs

• Glacial times: more GHGs are found in the ocean and in the land surface (consistent with a colder state)

• Interglacial times: these gases enter the atmosphere (consistent with a warmer state)

• Ranges were -10 K to +2 K relative to present temperatures

Considering the large recent increase in CH₄ and CO₂ raises a serious question of whether the temperature will rise out of the range seen in the previous million years

Contrast exponential growth and linear growth.

Exponential Growth: What we have seen population growth become (as time goes on our population growth was larger than in the years before)

Linear Growth: where in one year you add a certain amount then the next you add a certain amount, 100 million every year (what our population growth is starting to become)

What does doubling time mean?

How long it takes for a population to double in size

Where does almost all of the energy available on the earth's surface ultimately come from?

From the sun (the rest is from geothermal)

What does temperature measure?

• The average kinetic energy of particles in a substance

• Random molecular motion — kinetic energy of molecules running into each other

Sketch the global average vertical temperature profile of the earth's atmosphere. What are the names of each layer?

Note: temp on the x-axis, altitude on the y-axis

Troposphere: heated from below by sunlight reaching earth’s surface, so the temperature decreases upward in the troposphere

Stratosphere: heated from the absorption of UV by ozone (O₃), so temperature increases upward in the stratosphere

Mesosphere: temperature decreases upward in the mesosphere

Thermosphere: heated by extreme UV (AKA XUV), so the temperature increases upward into the thermosphere

In the vertical temperature profile, what accounts for the three temperature maxima?

The three maxima are there because we can divide the vertical temperature profile into three portions of the electromagnetic spectrum

XUV: absorbed in the thermosphere

UV: penetrates into the stratosphere, absorbed on the ozone layer

VIS + near IR: most of the energy is in this form; this goes right through the atmosphere and heats the surface (atmosphere is transparent to visible light)

Is there a constant output of radiant energy from the sun or is it variable?

Energy comes from a variable sun

On average it is 1367 [W/m²] but this varies by about ± 0.2 [W/m²] over the solar cycle

• We calculate there is 2 [W/m²] coming down because of anthropogenic influence

What are the “System International” (SI) units for mass, length, time and temperature?

Mass: [kg]

Length:[m]

Time: [s]

Temperature: [K]

What are the “System International” (SI) units for pressure, density, energy, power, and rate of transfer of electromagnetic radiation?

Pressure: Force/area=N/m²=(Kg*m/s²/m²)=Pascals

Density: Kg/m³

Energy: [J]

Power: [W]

Rate of transfer of electromagnetic radiation: [W/m²]

Express the freezing temperature of water and global average surface temperature in F, C and Kelvins.

Freezing point of water:             Average Surface Temperature:

               32 °F                                                      60 °F

                0 °C                                                       15 °C

                273 K                                                     288 K

What does 10³ kg m^-3 mean?

1000 kg/m³ = the density of water in scientific notation

How high up into our atmosphere do you have to go to put 1/2 of the molecules below you? At that level, what are the values of pressure and density? At that level, is the temperature colder or warmer than at the surface?

~5 km or 3 miles away

• ½ atmosphere pressure level = 500 m*bar

• density of 0.5 [kg/m³] at ~ 5 km

• At this level, the temperature is colder than at the surface (it is about 255 K which is the temperature at which the planet has to radiate to space to balance how much energy it gets from the sun (this is the Stefan Boltzmann law)

What balances the force of gravity to keep air parcels from accelerating toward the center of the earth?

Gravity pulls the molecules downward but what keeps it from happening is that there is a pressure gradient force (hydrostatic balance); air is a static fluid so for every particle in a profile you look at, the pressure is higher on the bottom and lower on top, giving a vertically direct pressure gradient force)

Hydrostatic Balance

When the force of gravity is balanced by the upward pressure gradient force, a very good approximation for most of our fluid envelopes

How dense are the ocean, human beings, and rocks?

Human beings and oceans are almost the same density (if we breath out we sink if we breath in we float)

Rocks: maybe three times as dense as water

How far down in the ocean do you have to go to add another 1 atmosphere of pressure?

About 10 [m]

What is the relationship between temperature and the wavelength of emitted electromagnetic radiation?

The energy of a photon is inversely proportional to its wavelength (more energy (hotter) = shorter wavelength)

What is shortwave radiation?

• Visible radiation

• Shorter than ~4μm

• characterizing electromagnetic radiation emitted at typical temperatures in the photosphere of the sun

What is longwave radiation?

• Infrared radiation

• longer than ~4μm

• characterizing electromagnetic radiation emitted at typical temperatures in the earth’s system

Stefan-Boltzmann Law

E=σT⁴

E = power of emitted radiation in W/m²

σ = 5.67×10^-8 [W/m²*K^-4] = Stefan-Boltzmann Constant

T = Temperature in Kelvin [K]

How hot is the photosphere of the sun?

About 6000 K (corresponds to yellow light)

How hot is the earth's surface?

about 288 K (10 microns in the infared)

How long is one micrometer (μm)?

It is 10^-6 meters

What does the Stefan-Boltzmann law imply about the relationship between temperature and the amount of electromagnetic energy coming from a body?

If you double the temperature you are going to emit 16 times as much radiation – negative feedback in the climate system

How does the intensity of electromagnetic radiation decrease away from a source?

Diluted by 1/r²

r = distance from source

Which photons are the most energetic?

Extreme Ultraviolet

What wavelengths are typically emitted from the sun?

0.5 microns (yellow-violet)

Which wavelengths carry most of the energy from the sun?

0.3 - 0.7 microns (visible light)

What wavelengths are typically reflected from the earth?

Visible light

What wavelengths are typically reflected from the moon?

If you can see the moon it is sunlight bouncing off the moon so it is visible light

What wavelengths are typically emitted from the earth's surface and from greenhouse gas molecules in the atmosphere?

Infrared (longer wavelengths)

What does transparent mean?

It means it transmits light

What does absorb and re-emit mean?

→Infrared transfer

Absorption: When electromagnetic radiation is absorbed by a substance (energy increases)

Emission: when electromagnetic radiation is emitted by a substance (energy decreases)

Which parts of the electromagnetic spectrum are most relevant to the ozone problem, and which to the greenhouse problem?

Ozone Problem: UV-Radiation is stopped by ozone layer

Greenhouse Problem: the energy comes to earth in the form of visible light and the emission is in the infrared

What is radiative equilibrium?

When the amount of electromagnetic radiation being absorbed by a body equals the amount being emitted (255 K)

What is albedo?

→Fraction of sunlight that bounces back (albedo of one means that all of the sunlight is reflected back; an albedo of 0 means all of the sunlight is absorbed by the object)

→Albedo(A) = (Reflected Sunlight)/(Incoming Sunlight)

What is the typical albedo of water, of clouds, and of the earth on average?

Water has a very low albedo (meaning it absorbs most of the sunlight) Albedo=0.1

Cloud Albedo= 0.5 (clouds are a major uncertainty in the atmosphere science because they sometimes have positive or negative feedback)

Earth: Albedo=0.3; depends on if there are trees, soil, etc. – Fraction of sunlight that stays in the earth’s system is about 70% being absorbed in the Earth’s system

Where does the factor of four come from in balancing absorbed solar radiation with emitted longwave radiation?

It comes from the geometry of a sphere (4πr² is the emitting area (the surface area of a sphere))

Why is Venus so hot at the surface?

Because Venus has a huge greenhouse effect (lots of carbon dioxide in its atmosphere)

How does an actual greenhouse work?

→ A glass-roofed greenhouse lets in visible light, which heats the interior of the greenhouse.

→ The warmed air cannot rise, so the roof acts as a physical barrier to convective heat transport by air motions, and the air inside stays warmer than outside the greenhouse.

How does the natural atmospheric greenhouse effect work?

→ The earth readily transmits visible light

→ The earth emits infrared light, but molecules in the atmosphere absorb and re-emit the infrared radiation back down to the surface.

→ This extra energy raises the temperature of earth’s surface.

How big is the natural greenhouse effect on the earth?

33 K (without an atmosphere we would be that much colder)

From about what altitude in the atmosphere is IR being emitted at 255 K?

At an altitude of about 5 km

What are the main greenhouse constituents in our present earth atmosphere?

Clouds (H₂O vapor), a little due to CO₂ in the atmosphere (CO₂ is increasing), CH₄, N₂O and industrial gases like HFCs

What is the “atmospheric window”?

The atmospheric window refers to specific ranges of wavelengths in the electromagnetic spectrum (specifically between 8-12 micrometers) that can pass through the Earth's atmosphere with minimal absorption, allowing infrared radiation to escape into space.

What gaseous constituents might “smear” this atmospheric window?

→ Human activities are increasing quantities of gases which absorb actively in the 8-12 μm band (the “window” where GHGs have less infrared absorption), “smudging” the atmospheric window, so that more infrared photons are absorbed, making the earth’s surface warmer

→ the gaseous molecules that will smear the atmospheric window are any complex molecules that have an absorption spectrum in this range (CFCs, N₂O)

What are some possible consequences of anthropogenic global warming?

• Surface temperatures warming

• Sea level rise

• Changes in large scale weather patterns

• Increased frequency of heat waves

• Changes in ocean circulation

• Rapid polar warming

• Changes in rainfall patterns

• etc.

How far are we from the sun?

150 million km

What is the radius of the earth?

6,367 km

Why are the poles cold and the equator hot?

Due to the sphericity of the earth’s shape, the sun’s rays are concentrated in the tropics and spread out at the poles as shown in the image.

How does the earth system deal with the fact that more short-wave energy comes into the tropics than long-wave energy is emitted, while the reverse is true of the high latitudes?

Atmospheric and oceanic heat transport arises in response to differential radiative heating, and acts to reduce temperature differences caused by differences in radiative heating

1) In the oceans, warm currents go poleward on the west edges of the ocean basins, and cold currents go equatorward on the east edges of the oceans

2) latent and sensible heat transport in the atmosphere, with warm moist tropical air moving poleward and being replaced by cold dry polar air moving equatorward

What is sensible heat transport?

Warm air is transported generally upward and poleward, while cold air is generally transported downward and equatorward

What is latent heat transport?

Moist air is transported generally upward and poleward, while dry air is generally transported downward and equatorward

About what fraction of solar energy reaching our planet goes into evaporation?

About 1/3 (35-40%) – a significant amount simply goes into evaporating water

How much energy does it take to evaporate 1 kg of water?

2.5 × 10⁶ J (2.5 million J; this is a lot of heat)

What are some of the differences between the properties of the land and the ocean?

Ocean can evaporate

Dry land will absorb heat it so it heats really quickly

Evaporation is the main difference – easier to heat and cool land surface compared to the ocean surface

It is much easier to warm and heat land than it is the ocean

What fraction of the earth's surface is covered by ocean?

About 70%

How can the land/sea differences explain the fact that earth is colder in January when it is closer to the sun?

In January, the land on the Northern Hemisphere is tilted away from the sun, so it cools quickly. Snow can build up on the land, causing it to reflect more sunlight so it gets cooler (ice albedo feedback)

In July, the NH land is tilted toward the sun, so it heats up quickly (more than compensating for the fact that the earth is farther from the sun)

In January the SH oceans heat slowly and cool slowly in july

What is a gyre?

Closed current circulations in the upper layer of the ocean driven by wind

-Westerly wind stress in midlatitudes

-Easterly wind stress in subtropics and bounded by continents

What is the thermocline? About how deep is it?

The depth at which the warm sunlit surface layer of the ocean transitions to the cold, deep ocean

Occurs around 100, 200 or 300 m where you can see a transition in the image

About how deep are the oceans?

about 5,000 meters

How does the ocean introduce a long time-scale into climate change issues?

There is a huge heat capacity of oceans (so whatever heat has been stored into the ocean stays there for a while)

A quarter of anthropogenic carbon release goes into the ocean, the ocean stores CO₂ for long periods of time:

• Whatever is in contact with the ocean’s surface (gases like CO₂) if it sinks to the bottom of the ocean it takes whatever in that water down (CO₂ from burning fossil fuels is going where ever it is coldest and saltiest enough to sink into the deep ocean — it stays in the ocean for a long (like a 1000 years) and when it comes back up, it exposes the atmosphere to whatever it had with it)

If the sea surface were warmer, would you expect more or less carbon dioxide and water vapor in the air?

Carbon dioxide dissolves into sea water preferentially where it is colder and where it is depleted of nutrients therefore it warmer surface means more GHGs in the air

How can the temperature of a nearby ocean control whether there is a desert or not?

The capacity of air to hold water grows exponentially with the temperature so if you are near warmer currents (east coast) with a lot more vapor in the air then you get a lot more rainfall. If you are on the west coast, near the the cold currents, the air cannot hold as much water

• Deserts occur on the west sides of continents commonly

What is a monsoon?

A seasonal reversal in the prevailing wind direction on a continental scale

Be able to sketch the relationship among the overturning circulation, warm and cold locations, and surface low and high pressure systems for winter or summer.

During winter the continents get much colder. The air over the continents becomes denser, more compact, and sinks, leaving room for air molecules to “fall off” of the expanded warm oceanic air columns onto the top of the contracted continental air columns. This increases the surface pressure over land and decreases it over the oceans. The resulting pressure difference causes the air to flow from the continents toward the oceans (offshore flow). The rising warm air over the oceans cools as it rises, leading to condensation and precipitation. The cold air over the continent warms somewhat as it sinks, which suppresses condensation and clouds.

What is the Walker circulation?

east-west overturning circulation in the tropics, with rising motion over Africa, Indonesia, and South America and sinking over the oceans; component of ENSO (based on the same principles as the monsoon)

What is the Coriolis effect?

Our reference frame on the earth’s surface around the rotation axis so straight-line motion appears to be curved (to the right in the Northern Hemisphere and to the left in the Southern Hemisphere)

In what direction does wind push the ocean surface layer in the northern hemisphere (Ekman transport)?

Ekman transport – wind stress on the upper layer of water causes it to move to the right (left) of the wind in the NH (SH), causing coastal upwelling on the west coasts of continents

On which side of the oceans does warm water move poleward?

On the west sides of oceans near east sides of continents

Where is upwelling most likely to occur?

Upwelling is the rise of seawater from the deep sections of oceans

On the east sides of the oceans or the west sides of continents (California and Peru)

Where are deserts most likely to occur?

On the west side of continents (where it is cool)

On which sides of the continents is it usually the rainiest?

On the eastern side of the continent when you are near the warm currents like the gulf stream

What controls the density of sea water?

How warm it is and how much salt is in it

Where is the ocean the warmest? Where is it the saltiest?

Warmest: Near the tropics and off the west edge of the ocean (gulf of Mexico is warm, pacific near Indonesia)

Saltiest: in the Atlantic

What physical processes can affect the salinity of water?

Settler driven evaporation or wind driven evaporation will increase the salinity; more precipitation will decrease the salinity; fresh water rivers flowing in will decrease the salinity; ice formation generally increases the salinity but when it melts it decreases the salinity

About how much salt is in a cubic meter of ocean water?

40 kg of salt in a m³ of water

What is the thermohaline circulation?

Slow overturning circulation in the ocean driven by differences in temperature (thermos) and salinity (haline)

Why does water tend to sink to the bottom preferentially in the North Atlantic?

Not enough rain here, evaporation in the sub-tropics, cooling at high-latitudes, and ice formation (makes more salty)

What is the "conveyor belt" idea?

This is a way to view the thermohaline circulation where there is sinking in the North Atlantic, spreading throughout the deep ocean (deep saline-rich current), rising, and returning to the surface of the North Atlantic ((less saline, shallow current)

Where is carbon dioxide entering the ocean and what does it do to the ocean?

Most of it is entering the deep ocean in the North Atlantic; it is then dissolved and forms carbonic acid and is slowly acidifying the ocean

What is El Nino? La Nina?

El Nino Southern Oscillation (ENSO) – A 3-7 year cycle seated in the equatorial Pacific basin with variations in sea level pressure, sea surface temperature, rainfall, strength of the Walker Circulation, and tilt of the thermocline

What is the Southern Oscillation?

– the atmospheric component of ENSO which involves variation in the difference in sea level pressure between Darwin, Australia and Tahiti (El Nino when this correspondence is weaker and La Nina when it is stronger)

What are the main characteristics of the tropical atmosphere and ocean during the cold phase of ENSO? During the warm phase?

Cold Phase: La Nina

• Strong Walker Circulation

• Steeply-sloping thermocline

• Cold SST/dry near Peru

• Wet near Indonesia

• Large Tahiti-Darwin SLP diff.

Warm Phase: El Nino

• Weak Walker Circulation

• Flat thermocline

• Warm SST/wet near Peru

• Dry near Indonesia

• Small Tahiti-Darwin SLP (sea level pressure) diff.

What are some practical reasons for trying to understand and predict ENSO?

• plan ahead to suppress fires

• Peru makes plans to offset fisheries and agriculture, U.S.

• If you live in Peru and you want to eat, you should know what you need to import fish or grow crops. El Nino is bad for fishing but good for growing crops in Peru

What is the Northern Annular Mode / North Atlantic Oscillation?

Northern Annular Mode (NAM): vertical coupling between the stratospheric polar night jet and tropospheric jet stream which varies between strong westerly flow and blocking highs with a disturbed polar vortex

North Atlantic Oscillation (NAO): – The component of NAM seated in the North Atlantic which describes the variation between a strong westerly