Greenhouse Effect continued…

We are still here.

Climate change

The knobs that control earth’s climate: • Atmospheric composi-on (greenhouse effect) • Amount of solar radia-on (luminosity) • What parts of Earth get radia-on (orbit) • Atmospheric and ocean circula-on • Earth’s albedo (frac-on of solar energy reflected off earth’s

surface) • Volcanoes • Plate tectonics

How much radiation we get depends on the angle at which the Sun’s rays hit the Earth, which:

• varies with latitude • varies with the season • varies with orbital parameters . . .

The same amount of sunlight is spread over a larger area at high latitudes

SunEarth

For more learning module, go to: http://www.windows2universe.org/earth/climate/sun_radiation_at_earth.html

Solar irradiance (the power per unit area received from the Sun) varies with latitude because of the curvature of the Earth’s surface. When you travel from lower latitude (e.g. equator) to higher latitude (e.g. Massachusetts, 42N), you will notice that, in the middle of the day, the sun is not directly shining above you. Instead, the angle of the solar insolation is much smaller in the higher latitude than in the lower latitude (see figure as well as previous slide). Since each ray of light carries the same amount of energy (342 W/m2), if the solar angle is smaller, this energy must be split across a wider area. Therefore, higher latitudes receive less solar irradiance than the lower latitudes. This partly explains why you feel that sunlight is stronger in Miami, Florida than in Quebec City in Canada!

Earth’s orbit

Also, solar irradiance varies seasonally. Why we experience seasons?

Seasonality occurs because the Earth’s axis is tilted 23.5° as it revolves around the Sun. This tilt causes the northern and southern hemispheres to tilt alternately toward and away from the Sun, and this motion causes seasonal changes in solar radiation received in each hemisphere. Therefore, from our Earth perspectives, incoming solar radiation varies with seasons.

The figure shows the tilt of Earth’s axis in its annual orbit around the sun causes the northern and southern hemispheres to lean directly toward and then away from the Sun at different times of the year.

Earth’s orbit

This change in relative position causes seasonal shifts between the hemispheres in the amount of solar radiation received at Earth’s surface. Especially, from our Earthbound perspective, this orbital motion causes a shift of the overhead Sun through the tropics from a latitude of 23.5°N on June 21 to 23.5°S on December 21. This change in the Sun’s angle results in large seasonal changes in the amounts of solar radiation (W/m2) received on Earth.

This figure shows the latitudinal solar radiation energy received from January (J) to December (D). The high energy zone shifts as seasons migrate. During northern hemisphere spring/summer (April – August), the high energy zone shifts from equator to ~40N. The opposite happens during the southern hemisphere spring/summer.

Earth’s orbit – eccentricity

Further, Earth’s actual orbit is not a perfect circle. It has a slightly eccentric or elliptical shaped. This shape of Earth’s orbit around the Sun has varied in the past, becoming at times more circular and at other times more elliptical (eccentric). This change in orbital shape also contributes to changes in seasonality, and is called eccentricity.

Eccentricity:

Obliquity:

Precession:

Orbital effects

Cause slight adjustments in timing and location of radiation.

Combined, these cause Milankovitch cycles

The figures here summarize other important orbital effects that contribute to climate change on Earth (Eccentricity, Obliquity, and Precession). These are known as Milankovitch Cycles, named after Serbian astrophysicist, Milutin Milankovic, who found their cyclicity. They are important climate forcings to understand longer time scales (e.g. thousands to millions of years). However, long term climate change is beyond the scope of this course and, therefore, will not be included in future Tests.

Each of the successive time scales reveal short oscillations embedded within longer ones, just as cycles of daytime heating and nighttime cooling are embedded in the longer seasonal cycle of summer warmth and winter cold. Referring to past variability and understanding the factors contributing to those variability = paleoclimatology. In this course, we focus on relatively short response time periods that affect us more recently and in our near future.

Response times of Climate Components

This table shows examples of different climate components with various response times.

(continue)

August Arctic Ocean Ice Extent

Source: NSIDC

(con%nued)

Now, we revisit the figure showing sea ice extent in the Arc%c. It is obvious that the decrease in sea ice extension occurred within just the past few decades.

What is the forcing (climate knobs) for this, and is this a slow or fast response?

The Atmosphere Gas Name Chemical Formula Percent Volume Nitrogen N2 78.08%

Oxygen O2 20.95%

*Water H2O 0 to 4%

Argon Ar 0.93%

*Carbon Dioxide CO2 0.0390%

Neon Ne 0.0018%

Helium He 0.0005%

*Methane CH4 0.00017%

Hydrogen H2 0.00005%

*Nitrous Oxide N2O 0.00003%

*Ozone O3 0.000004%

*affected by people

We learned that the three major components of the atmosphere are nitrogen, oxygen, and argon, which compose over 99.9 % of the Earth’s entire atmosphere, but none are a greenhouse gas. In contrast, the most important greenhouse gases, which are water vapor (H2O), carbon dioxide (CO2), and methane (CH4), make up only a fraction of the atmospheric composition.

CO2 emissions by country

Very interesting map as the area of each country represents the amount of CO2

emissions (updated in 2008). This figure indicates that the US, EU countries, India,

China, South Korea, and Japan are particularly responsible for the large amount of

CO2 added to the atmosphere. https://www.grida.no/resources/5437

Both CO2 and CH4 trap part of Earth’s back radiation, keep the heat in the

atmosphere, and make Earth warmer than it would otherwise be. And this

warming in turn activates the positive feedback effect of water vapor (H2O). Due to

the importance of this positive feedback, water vapor is considered to be the most

concerning greenhouse gas.

CO2 is also important when we consider future climate change as human emissions

of CO2 are driving climate change. This figure shows major countries emitting CO2

since 1950 in billions tons. The U.S. is THE largest contributor of the CO2 emission.

Methane (CH4) is a second important atmospheric greenhouse gas. It has many

sources, including swampy lowland bogs, rice paddies, the stomachs and bowels of

cows, digesting vegetation, termites, and the decay of organic matter in an oxygen-

free (anaerobic) environment.

Greenhouse Gas Concentra.ons

Industrial Revolution 1750-1850 AD

Carbon dioxide and other greenhouse gas (e.g. CO2, CH4, N2O) variability between 0 to 2005 AC. Please take notice of the abrupt increasing that occurred between 18th to mid-19th – at the time of the Industrial Revolution!

Industrial Revolution

▪ The Industrial Revolution was a period from 1750 to 1850 where changes in

agriculture, manufacturing, mining, transportation, and technology had a

profound effect on the social, economic and cultural conditions of the times.

▪ It began in the United Kingdom, then subsequently spread throughout

Western Europe, North America, Japan, and eventually the rest of the world.

▪ The Industrial Revolution marks a major turning point in history; almost

every aspect of daily life was influenced in some way.

▪ Most notably, average income and population began to exhibit

unprecedented sustained growth.

▪ In the two centuries following 1800, the world's average per capita income

increased over tenfold, while the world's population increased over sixfold

▪ Major innovations: steam power, iron making, textiles

The shapes of the blackbody

spectra of Earth and the sun

Percentage of radiation

absorbed through the atmosphere

Absorption Spectra of Greenhouse Gases

To fully understand the greenhouse effect, we need to understand, once more, about

blackbody radia9on. As we learned earlier, the radia9on emi<ed by a blackbody has

a characteris9c wavelength distribu9on that depends on the body’s absolute

temperature (the Earth’s blackbody radia9on = infrared wavelength).

In the lowest figure “Percentage of radia9on absorbed through the atmosphere”,

absorp9on of 100% means that no radia9on penetrates the atmosphere. CO2, O3,

N2O, CH4, H2O are the media that absorb associated wavelength energy – and we

now know that these media are called greenhouse gases! As you see, part of the

shortwave radia9on from the Sun is almost 100% absorbed by ozone (O3) and oxygen

molecules (O2) in the stratospheric ozone layer!

Supplemental reading: What is Ozone? NASA Goddard Space Flight Center,

h<ps://ozonewatch.gsfc.nasa.gov/facts/SH.html

Greenhouse Effect continued…

We are still here.

Climate change

The knobs that control earth’s climate: • Atmospheric composition (greenhouse effect) • Amount of solar radiation (luminosity) • What parts of Earth get radiation (orbit) • Atmospheric and ocean circulation • Earth’s albedo (fraction of solar energy reflected off earth’s

surface) • Volcanoes • Plate tectonics

We talked about climate knobs that effectively control our climate system. Rather than to understand the chaotic and complicated systems that interact with the climate system as a whole, a better way to understand climate is to focus on components (climate knobs) that strongly affect the climate system. Here, let’s learn about the first climate knobs.

Air Pollution

Smog trapped below clouds by a thermal inversion across upstate New York

Image from NASA Johnson Space Center

Although the atmosphere is a renewable resource, the atmosphere is very fluid and definitely not stable. It is the most dynamic of all of Earth’s systems. We, as human beings, both use and abuse the atmosphere. It is treated as a gigantic waste disposal system for emissions from our vehicles and industries. How people affect the atmosphere and influence global climate has become a major environmental concern for many around the world.

EOS, December 2014

The Atmosphere Gas Name Chemical Formula Percent Volume Nitrogen N2 78.08%

Oxygen O2 20.95%

*Water H2O 0 to 4%

Argon Ar 0.93%

*Carbon Dioxide CO2 0.0390%

Neon Ne 0.0018%

Helium He 0.0005%

*Methane CH4 0.00017%

Hydrogen H2 0.00005%

*Nitrous Oxide N2O 0.00003%

*Ozone O3 0.000004%

*affected by people

The most important greenhouse gases are water vapor (H2O), carbon dioxide (CO2), and methane (CH4), and they consist of only a fraction of the entire atmosphere’s composition. While water vapor can range to above 3% in the moist tropics, it is less than 1% of the atmosphere in a dry/cold environment. All of these greenhouse gases make up, on average, less than 1% of the atmosphere, and are referred to as trace gases. Although small, these gases are important in how they can impact and alter the Earth’s energy budget. Here, green-colored gases are human influenced greenhouse gases. While we are primarily talking about trace gases, it is important to note that not all trace gases are greenhouse gases.

Climate change

The knobs that control earth’s climate: • Atmospheric composition (greenhouse effect) • Amount of solar radiation (luminosity) • What parts of Earth get radiation (orbit) • Atmospheric and ocean circulation • Earth’s albedo (fraction of solar energy reflected off earth’s

surface) • Volcanoes • Plate tectonics

The Sun as a source of Energy The sun is the ultimate source of energy in our solar system. Almost all energy originates from the Sun.

• Nuclear Fusion – Hydrogen is converted

to Helium releasing tremendous energy

– 3.9 X 1026 W (watt)!

– Average distance to the Earth is ~150 X 106 km

– Surface temp. is 5800 K (kelvin)

Nuclear Fusion: At the core of the Sun, tremendous amounts of nuclear power are generated by a reaction known as nuclear fusion. Nuclear fusion is the process by which two or more smaller atomic nuclei combine to form a larger one, with an accompanying release of energy. Fusion is a process where a simple hydrogen nuclei containing one proton fuses to produce helium. Fusion is a clean energy producing process and can be used as an alternative energy source in the future. However, the process is currently too expensive to be widely commercialized.

The Sun is a natural fusion reactor, which produces magnificent amounts of energy and it’s clean energy!

For more information about nuclear fusion, pleas visit: https://energyeducation.ca/encyclopedia/Nuclear_fusion_in_the_Sun

Diagram showing the different parts of the Sun. The three parts of the atmosphere, from the surface of the Sun outward are the photosphere, chromosphere, and corona. (Credit: NASA)

Further reading about the Sun: https://imagine.gsfc.nasa.gov/science/objects/sun1.html

Video link: NASA -Introduction to the Electromagnetic Spectrum https://youtu.be/lwfJPc-rSXw

Energy travels by means of light through space in the form of waves called electromagnetic radiation. These waves span many orders of magnitude in size, or wavelength, and this range of wave sizes is known as the electromagnetic spectrum.

Energy travels by means of light through space in the form of waves. Photon – an elementary particle – carries this energy in the form of a wave. This is called electromagnetic radiation.

These waves span many orders of magnitude in size, or wavelength, and this range of wave sizes is known as the electromagnetic spectrum.

Absorption Spectra of Greenhouse Gases

Energy from the Sun moves through space in a wide range of wave forms that vary by wavelength (electromagnetic spectrum). However, the energy that drives Earth’s climate system occupies only a narrow range of this spectrum. Much of the incoming radiation energy from the Sun is scattered, reflected, or absorbed by the atmosphere. By the time it reaches the surface of the Earth, it mostly consists of visible radiation at wavelengths between 0.4 and 0.7 micrometers. Also, some ultraviolet radiation enters Earth’s atmosphere. Both are sometimes referred to as shortwave radiation (blue band in figure). Infrared radiation is a longer wavelength than visible and ultraviolet radiation and referred to as longwave radiation (red band in figure).

The shapes of the blackbody

spectra of Earth and the sun

Percentage of radiation

absorbed through the atmosphere

Absorption Spectra of Greenhouse Gases

If a chunk of matter oscillates and can interact with light at all possible frequencies, it is called a blackbody. The light (energy) that is emitted by a blackbody is called blackbody radiation. Most solids and liquids at the surface of the Earth are blackbodies. Blackbody radiation is made up of a characteristic distribution of frequencies of infrared light (red band in figures).

Thus, Earth not only absorbs energy, it emits the energy back to the space.

In the middle figure, “the shapes of the blackbody spectra of Earth and the Sun” show the band of wavelength the Sun shines with surface temperature 5800 kelvin (K) (blue band) and Earth shines in infrared light (red band) with mean surface temperature 255 K (= -18 C°, -0.4 F).

The lowest figure, “percentage of radiation absorbed through the atmosphere” explains the basics of greenhouse effect. We will come back to this later!

Blackbody (Planck) Curve

Sun’s planetary temperature 5800 K or 5526 C Incoming solar radiation = shortwave radiation

Earth’s planetary temperature 255 K or -18 C Earth’s outgoing radiation = longwave radiation

The wavelength distribution of blackbody radiation can be described mathematically by a relation called the Planck function, thus called blackbody curve or Planck curve. The important message from this figure is the spectrum of blackbody radiation is dependent on the temperature of the object. A higher temperature blackbody radiates higher energy in a shorter wavelength than a lower temperature object.

Example Test 1 question: An idealized object that absorbs all incident electromagnetic radiation and emits the maximum amount of radiation possible at every wavelength for its temperature is a(n):

A. blackbody B. isotherm C. celsius D. albedo E. kelvin

The answer is A!

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