Chapter 3: cause of climate change

Question 1

Climate changes whenever

Answer 1

the earth’s energy balance (balance between incoming radiation from the Sun and outgoing terrestrial radiation from the Earth) is disturbed.

Question 2

climate forcing

Answer 2

Any process that can disturb the earth’s energy balance and forces the climate to change,

Question 3

Climate forcing can be separated into

Answer 3

internal and external types

Question 4

External forcing

Answer 4

operates from outside the Earth’s climate system, and includes changes in the global energy balance due to variations in the Earth’s orbit around the Sun, and changes in the amount of energy coming from the Sun.

Question 5

Internal forcing

Answer 5

operates from within the climate system, for example the change in the global energy balance due to changes in the composition of the atmosphere.

Question 6

Thus, external forcing is mainly because of

Answer 6

natural processes

Question 7

internal forcing may be due to

Answer 7

either natural (e.g., volcanic eruptions) or anthropogenic (e.g., changes in atmospheric composition) processes

Question 8

In general, climate changes prior to the Industrial Revolution can be explained by

Answer 8

natural causes, such as changes in solar energy, volcanic eruptions, and natural changes in greenhouse gas (GHG) concentrations.

Question 9

Recent climate changes, however, cannot be explained by natural causes alone. Research indicates that natural causes are very unlikely to explain most observed warming, especially warming since the mid‐20th century

Answer 9

Rather, human activities can very likely explain most of that warming

Question 10

compare between models

Answer 10

Models that account only for the effects of natural processes are not able to explain the warming over the past century. Models that also account for the greenhouse gases emitted by humans are able to explain this warming.

Question 11

External causes include changes in

Answer 11

the global energy balance due to:

• orbital variations and
• changes in the solar activity

Question 12

“Milankovitch Cycles (orbital variations)”

Answer 12

On timescales of a millennium and longer, changes in the character of the Earth’s orbit around the Sun can significantly affect the seasonal and latitudinal distribution of incoming solar energy

Question 13

“Milankovitch Cycles (orbital variations)” The change in energy receipt can amount to

Answer 13

10% or more in certain locations

Question 14

The Milankovitch Cycles force the changes between

Answer 14

ice age and warmer conditions on Earth, on time scales of 10,000 to 100,000 years

Question 15

The last Ice Age occurred ……………….. years ago

Answer 15

18,000

Question 16

Thus, ………………………………………… can be best explained by Milankovitch’s Astronomical theory

Answer 16

fluctuations in the Earth’s orbit which can upset the energy balance of the climate system

Question 17

The Milankovitch’s Astronomical theory is based on

Answer 17

three variations in the position of Earth relative to the Sun:

• Tilt of the Earth’s axis
• Eccentricity of the Earth’s orbit
• Orbital precession

Each of these variations has its specific time period and affect the earth’s energy balance, thus forcing the climate to change.

Question 18

Tilt of the Earth’s axis (Earth’s obliquity)

Answer 18

• Today the Earth is tilted on its rotational axis at an angle of 23.5° relative to a perpendicular to the orbital plane of Earth.
• The tilt varies between 21.5^o and 24.5^o over a period of 41,000 years.
• Obliquity does not influence the total amount of solar radiation received by the Earth, but it affects the distribution of insolation in space and time

Question 19

Increasing tilt amplify

Answer 19

the strength of the seasons, especially at the poles.

• As obliquity increases, the amount of solar radiation received at high latitudes increases during summers and decreases during winters.
• Changes in obliquity have little effect at low latitudes, since the strength of the effect decrease towards the equator.

Question 20

the strength of the seasons, especially at the poles.

• As obliquity increases, the amount of solar radiation received at high latitudes increases during summers and decreases during winters.
• Changes in obliquity have little effect at low latitudes, since the strength of the effect decrease towards the equator.

consequently, variations in the earth’s axial tilt affect the

Answer 20

strength of the latitudinal temperature gradient.

Question 21

Increased tilt has the effect of

Answer 21

raising the annual receipt of solar energy at high latitudes, with a consequent reduction in the latitudinal temperature gradient

Question 22

Eccentricity of the Earth’s orbit

Answer 22

The Earth’s orbit has been found to vary from being near circular (e = 0.005) to markedly elliptical (e = 0.06) over periodicities of approximately 100,000 and 413,000 years.

Question 23

Variations in eccentricity influence

Answer 23

the total amount of solar radiation incident at the top of the Earth’s atmosphere at perihelion and aphelion.

Question 24

For example, the present ellipticity of the Earth’s orbit with a 3% difference in distance causes a

Answer 24

6% difference in solar energy between perihelion and aphelion.

Question 25

With maximum ellipticity, the energy received at ………….. would be …………….. % greater than that at ……………..

Answer 25

perihelion

20% to 30%

aphelion

Question 26

Orbital precision (precision of equinoxes)

Answer 26

Due to the gravitational interaction of other planets, primarily the Moon and Jupiter, the perihelion moves in space with a consequent shifting or precession of the elliptical orbit.

Question 27

This precession causes

Answer 27

the equinoxes to move around Earth’s orbit, completing on full 360^o orbit around the Sun every 23000 years.

Question 28

Effects of the precision of equinoxes

Answer 28

• Like obliquity, precession does not affect the total amount of solar energy received by the Earth, but only its hemispheric distribution over time.
• Due to orbital precision, after 11,000 years NHS summer occur at perihelion with the north pole is tilted towards the Sun. This results in more hotter summers.

Question 29

Sunspots are

Answer 29

cooler areas on the sun’s surface (the photosphere), which are associated with strong local magnetic activity

Question 30

faculae

Answer 30

associated with sunspots are the brighter and hotter areas called faculae, which increase the solar irradiance.

Question 31

sunspot cycles

Answer 31

The periodic changes (11 or 22 years) in the sunspot number

Question 32

The total solar energy flux, is related to the sunspot cycle as follows:

Answer 32

Question 33

Internal causes include

Answer 33

changes in the global energy balance due to:

• volcanic activity (natural) and
• changes in atmospheric composition (natural and anthropogenic)

Question 34

Volcanic activity is an example of

Answer 34

internal (natural) climate forcing

Question 35

Explosive volcanic eruptions can

Answer 35

inject large quantities of dust and sulphur dioxide, in gaseous form, into the upper atmosphere, the stratosphere, where the sulphur dioxide is rapidly converted into sulphuric acid aerosols.

• Volcanic pollution (from smaller eruptions) in the lower atmosphere is removed within days by rain
• However, the volcanic dust and aerosols in the stratosphere may remain for several years, gradually spreading over much of the globe

Question 36

Volcanic pollution results in

Answer 36

a 5 to 10% reduction in the direct solar beam, largely through scattering as a result of the highly reflective sulphuric acid aerosols.

Question 37

Large eruptions, such as the Mount Pinatubo (Philippines) eruption in 1991, can bring about

Answer 37

a global cooling of up to 0.3°C lasting for up to 2 years.

Question 38

The changing composition of the atmosphere, particularly its ……………………….. is a well‐known example of internal climate forcing

Answer 38

greenhouse gas content

Question 39

Greenhouse gases absorb

Answer 39

terrestrial, long‐wave radiation from the Earth and reemit this radiation up to space and down to the surface.

• The increase in the amount of downward energy warms the surface creating the greenhouse effect.

Question 40

A change in the greenhouse gas content of the atmosphere will affect

Answer 40

the energy balance of the climate system. For example, if the amount of carbon dioxide is increased, more out‐going radiation will be trapped in the atmosphere.

Question 41

A change in the greenhouse gas content of the atmosphere will affect the energy balance of the climate system. For example, if the amount of carbon dioxide is increased, more out‐going radiation will be trapped in the atmosphere.

 To restore the energy balance between energy coming from the Sun and energy leaving the Earth,

Answer 41

the temperature of the atmosphere rises

Question 42

To restore the energy balance between energy coming from the Sun and energy leaving the Earth, the temperature of the atmosphere rises.

 This enhances

Answer 42

the Earth’s natural greenhouse effect. Changes in the concentrations of greenhouse gases can occur in numerous ways.

• Natural changes in the carbon dioxide content of the atmosphere occurred at the end of the last Ice Age in response to the Milankovitch Cycles.
• Mankind, through energy generation, changing land use and other processes, has produced a substantial change in the atmospheric composition over most recent centuries, causing a major shift in global climate (global warming).