Download Chapter 4: Insolation and Temperature

Chapter 4: Insolation and Temperature
I.
II.
The Impact of Temperature on the Landscape
A. all organisms have certain temperature tolerances
B. most inorganic components of landscape are affected by long-run
temperature conditions
1. temperature is a basic factor in soil development
2. repeated temperature fluctuations are prominent cause in breakdown
of exposed bedrock
Energy, Heat and Temperature
A. Energy
1. energy: ability to do work
2. anything that changes the state or condition of matter
3. kinetic energy: the energy of movement
a. constant movement of molecules in all substances
b. associated with how hot or cold something is
c. increased kinetic energy results in a substance warming up
B. Temperature and Heat
1. temperature
a. description of the average kinetic energy of the molecules in a
substance
b. degree of hotness or coldness of a substance
c. more vigorous the jiggling of the molecules, the higher the
temperature of a substance
2. heat/thermal energy
a. energy that transfers from one object or substance to another
because of a difference in temperature
b. energy transferred from object with higher temperature to object
with lower temperature
C. Measuring Temperature
1. Fahrenheit Scale
a. sea level freezing point of water = 32oF
b. sea level boiling point of water = 212oF
2. Celsius Scale
a. component of International System of measurement (SI)
b. sea level freezing point of water = 0oC
c. sea level boiling point of water = 100oC
d. conversions:
1) oF = (oC x 1.8) + 32o
2) oC = (oF – 32o)/1.8
3. Kelvin Scale
a. measures absolute temperature
1) scale begins at absolute zero, the lowest possible temperature
2) absolute zero: temperature at which molecules have their
minimum kinetic energy
3) 100o range between the freezing and boiling points of water
Chapter 4: Insolation and Temperature – p. 2 of 14
III.
4) there are no negative values
b. conversions
1) oC = oK – 273o
2) oK = oC + 273o
Solar Energy
A. Intro
1. the sun supplies essentially all the energy that drives most of the
atmospheric processes on Earth
2. unequal heating of the Earth by the sun puts the atmosphere in
motion and is responsible for the most fundamental patterns of
weather and climate
3. the sun produces energy by nuclear fusion
B. Electromagnetic Radiation
1. form of sun’s radiant energy
2. does not require a medium for transmission
3. speed of light = 186,000 mi/sec; energy travel time sun to Earth = 8 mins
4. wavelength: distance from the crest of one wave to the crest of the next
5. electromagnetic spectrum: electromagnetic radiation of all wavelengths (Fig 4-5)
6. 3 areas of spectrum of particular interest to physical geographer
a. visible light
1) fairly narrow band with wavelength: 0.4 – 0.7 µm (micrometers)
2) comprises 47% of energy from sun to Earth (Fig 4-5)
b. ultraviolet waves
1) wavelength: 0.01 – 0.4 µm
2) just shorter than human eye can sense
3) comprises 8% of total energy coming from the sun to Earth
4) much absorbed by ozone layer of the atmosphere
c. infrared waves
1) wavelength: 0.7 – 1,000 µm (1mm)
2) just longer than human eye can sense
3) range:
a) from short/near infrared
b) to thermal infrared
4) comprises 45% of total energy from sun to Earth
7. shortwave radiation
a. solar radiation is almost completely in the form of visible light,
ultraviolet and short infrared radiation
b. virtually all solar radiation is shortwave radiation
8. longwave radiation
a. all terrestrial radiation (radiation emitted by earth) is longwave
radiation (4µ is wavelength boundary between shortwave and
longwave radiation)
b. entirely in the thermal infrared portion of spectrum
C. Insolation
1. incoming solar radiation
Chapter 4: Insolation and Temperature – p. 3 of 14
IV.
V.
2. solar constant: the fairly constant amount of solar insolation
(averaged over a year) received at the top of the atmosphere
a. 1372 watts per square meter (W/m2) = 1 calorie/cm2
1) 1 watt = 1 joule/sec
2) 1 joule = 0.239 calories
3) calorie: amount of heat required to raise temperature of 1 gram of
water (at 15oC) by 1oC
Solar Power
A. solar energy
1. during a 24 hour day, an average of 164 watts of solar energy strikes
each square meter of Earth’s surface – enough energy to meet the
electrical generation needs of the entire planet
2. overall solar power provides only 0.1% of the global energy
B. photovoltaic cells
1. advantages:
a. low capital cost
b. requires little maintenance
c. no energy source other than sun is required to create electricity
d. potential for decentralized energy electrical generation
2. disadvantages:
a. only 15-12% efficient: capture a limited portion of the solar
spectrum; a sizable amount of captured photon energy is lost as
heat
b. solar dependent: limited electrical generation capacity when
cloudy/hazy, none when it’s dark
Basic Heating and Cooling Processes in the Atmosphere
A. Radiation
1. radiation: process by which electromagnetic radiation is emitted from
an object
2. hotter objects, such as our sun, emit more energy at shorter
wavelengths
3. cooler bodies, such as Earth, radiate mostly long waves
4. black body: a body that emits the maximum amount of radiation
possible at every wavelength
a. perfect radiators; radiate with almost 100% efficiency
b. the sun and Earth function essentially as black bodies
c. the atmosphere is not as efficient a radiator as the sun or Earth’s surface
B. Absorption
1. absorption: the ability of an object to assimilate energy from
electromagnetic waves that strike it
2. the temperature of on object increases when energy is absorbed
3. good radiators tend to be good absorbers; poor radiators tend to be
poor absorbers
4. good absorbers: sun, Earth, mineral matter (rock, soil); darker colors;
water vapor and CO2
5. poor absorbers: snow, ice, lighter colors, nitrogen
Chapter 4: Insolation and Temperature – p. 4 of 14
C. Reflection
1. reflection: ability of an object to repel electromagnetic waves without
altering either the object or the waves
2. good absorbers are poor reflectors, and vice versa (explains unmelted
snow on a sunny day)
D. Scattering
1. scattering: deflection of electromagnetic waves that involves a change
in direction but no change in wavelength
2. amount of scattering depends on wavelength as well as size, shape,
and composition of the molecule or particulate
3. shorter waves are more readily scattered than longer ones by
atmospheric gases
a. Rayleigh scattering: scattering of shortest wavelengths of visible light,
violet and blue
b. violets and blues more likely to be scattered in the visible part of
spectrum  blue skies
c. more atmosphere to traverse at sunrise/sunset  orange/red skies
d. Mie scattering: scattering of almost all wavelengths of visible light by
larger particles that results in sky appearing gray
E. Transmission
1. transmission: process whereby electromagnetic waves pass
completely through a medium
2. transmission variability
a. poor transmitter: Earth materials
b. good transmitter: water
3. greenhouse effect
a. transmission generally depends on wavelength of radiation
b. glass
1) readily transmits shortwave radiation but not longwave radiation
2) that’s why heat builds up in a closed automobile
F. greenhouse effect: the trapping of heat in the lower troposphere
because of differential transmissivity for short and long waves
1. greenhouse gases readily transmit incoming shortwave radiation
from the sun but do not easily transmit outgoing longwave
terrestrial radiation
2. most important greenhouse gases: water vapor and CO2
3. terrestrial radiation is absorbed by greenhouse gases and reradiated back
toward the surface, delaying the energy loss to space
4. one of the most important heating processes in the troposphere
a. w/o greenhouse effect, Earth’s average temperature would be 5oF
(rather than current average = 59oF)
b. global warming: increase in CO2 atmosphere resulting in an increase
in the average global temperature
G. Conduction
1. conduction: movement of heat energy from one molecule to another
without changes in the relative position of the molecules
Chapter 4: Insolation and Temperature – p. 5 of 14
VI.
a. enables heat to be transferred from one part of a stationary body to
another or from one object to a second object when the 2 are in contact
b. results from molecular collision
c. when 2 molecules of unequal temperature are in contact with one
another, heat passes from the warmer to the cooler until they
attain the same temperature
2. variation in ability to conduct
a. good conductors: metals
b. poor conductors: earth materials, air
2) only air layer touching the ground is heated much
3) dry air is a less efficient conductor than moist air
H. Convection
1. convection: heat is transferred from one point to another by the
predominantly vertical circulation of a fluid (including air)
a. heated molecules move from one place to another
b. convection causes warm air to rise
c. convection cell: updraft of warm air and a downdraft of air after it has cooled
I. Advection: when the dominant direction of heat transfer in a moving
fluid is horizontal
J. Adiabatic Cooling and Warming
1. whenever air ascends or descends its temperature changes due to a
variation in pressure
2. Expansion: Adiabatic Cooling: cooling by expansion in rising air
a. increased altitude  decreased air pressure  expansion 
reduced collisions  temperature drop
b. adiabatic: without the gain or loss of heat
c. in the atmosphere any time air rises it cools adiabatically
3. Compression: Adiabatic Warming: warming by compression in
descending air
a. decreased altitude  increased air pressure  compression 
increased collisions  temperature rise
b. in the atmosphere any time air descends it warms adiabatically
c. adiabatic cooling of rising air: one of the most important processes in
cloud development and precipitation
K. Latent Heat
1. latent heat: energy stored or released when a substance changes
state
2. evaporation: liquid water is converted to gaseous water vapor
a. energy is stored
b. cooling process
3. condensation: gaseous water vapor condenses to liquid water
a. energy is released
b. warming process
The Heating of the Atmosphere
A. there is an annual balance between incoming and outgoing radiation
Chapter 4: Insolation and Temperature – p. 6 of 14
1. incoming shortwave radiation and outgoing longwave radiation
are in a long-term balance (total amount of insolation received by
Earth and its atmosphere equals the total amount of terrestrial
radiation returned to space)
2. global energy budget: annual balance between incoming and
outgoing radiation for the entire globe
B. Earth’s energy budget (using 100 units to represent total insolation at
top of atmosphere) (Fig 4-17)
1. incoming shortwave solar radiation = 100
a. albedo = 31
1) albedo: reflectivity of an object
2) Earth’s albedo: the fraction of total solar radiation that is reflected
back, unchanged, into space
3) almost 1/3 of the incoming solar radiation is reflected back into
space without being absorbed or altered
b. absorbed by Earth’s atmosphere = 24
1) absorbed by the ozone layer = 3
2) absorbed by the rest of the atmosphere = 21
3) this energy heats the Earth’s atmosphere directly
c. absorbed by Earth’s surface = 45
1) almost half the incoming solar radiation passes through the Earth’s
atmosphere and is absorbed by Earth’s surface
2) this energy heats the Earth’s surface
2. outgoing radiation lost to space = 100
a. albedo = 31
b. longwave radiation emitted to space by the atmosphere = 61
1) incoming radiation that heats atmosphere directly = 24
a) radiation absorbed by ozone in the atmosphere and reemitted
as longwave radiation= 3
b) radiation absorbed directly by atmosphere and reemitted as
longwave radiation= 21
2) energy transferred from Earth’s surface to the atmosphere by
conduction and convection = 4
3) heat transferred from Earth’s surface to the atmosphere through
latent heat in water vapor = 19
4) net atmospheric gain of energy through absorption of terrestrial
radiation (longwave) by greenhouse gases = 14
a) radiation from Earth’s surface to the atmosphere = 110
b) radiation from the atmosphere to Earth’s surface = 96
c. longwave radiation emitted from Earth’s surface transmitted
directly through atmosphere (atmospheric window) without being
absorbed = 8
3. atmosphere heated mostly from below rather than from above
a. sun is original source of energy
b. atmosphere mostly heated from longwave radiation emitted from
surface of Earth
Chapter 4: Insolation and Temperature – p. 7 of 14
c.  troposphere in which cold air overlies warm air  constant
convective activity and vertical mixing
VII. Focus: Monitoring Earth’s Radiation Budget
A. AVHRR (Advanced Very High Resolution Radiometer) sensors aboard
permanent orbiting satellites monitor Earth’s radiation budget
B. available solar energy (Fig 4-C)
1. total incoming shortwave radiation measured at top of the
atmosphere measured in watts per square meter (W/m2)
2. influenced only by angle of sun and number of hours of daylight
3. highest average daily insolation in June occurs over the Arctic: low
solar angle of incidence but 24 hours of daylight
C. absorbed solar energy (Fig 4-D)
1. total amount of shortwave energy absorbed by the atmosphere and
surface
2. difference between the total shortwave energy at the top of the
atmosphere and the total shortwave radiation reflected back to space
3. high absorption in subtropical latitudes
D. outgoing longwave radiation (Fig 4-E)
1. nighttime emission of longwave radiation
2. very high in subtropical and Midlatitude desert regions in
southwestern US, northern Africa and east-central Eurasia: because
of clear nighttime skies and low water vapor content of air
VIII. Variations in Heating by Latitude and Season
A. Intro
1. latitudinal and vertical imbalances in the energy budget are among
fundamental causes of weather and climate variations
2. radiation differences  temperature differences  air density differences 
pressure differences  wind differences  moisture differences
3. world weather and climate differences caused by unequal heating of
Earth and its atmosphere that is the result of latitudinal and seasonal
variation in how much energy is received by Earth
B. Latitudinal and Seasonal Differences
1. Angle of Incidence
a. angle of incidence: angle at which rays from the sun strike the Earth
b. primary determinant of intensity of solar radiation at any spot on Earth
c. the closer to 90o the angle of incidence, the smaller the surface
area heated by a given amount of insolation and the more effective
the heating
d. insolation received by high latitude regions is much less intense
than that received by tropical areas during the year as a whole
2. Atmospheric Obstruction
a. sunlight received at Earth’s surface is half as strong as at the top
of Earth’s atmosphere on average
b. factors influencing:
1) path length (amount of atmosphere radiation has to pass through –
determined by angle of incidence)
Chapter 4: Insolation and Temperature – p. 8 of 14
IX.
2) transparency of the atmosphere
c. depletes solar radiation more in high latitudes than low latitudes
3. Day Length
a. longer days allow more insolation to be received and thus more
heat absorbed
b. in mid and high latitudes there are pronounced seasonal differences
C. Latitudinal Radiation Balance (Figs 4-21 and 4-22)
1. energy surplus in low latitudes, from 28oN to 33oS, where there is
consistently high angle of incidence
2. energy deficit in latitudes poleward of 28oN and 33oS is associated
with low angles of incidence
3. world radiation variations largely latitudinal with interruptions based
on presence or absence of frequent cloud cover
4. incoming and outgoing radiation for Earth-atmosphere complex as a
whole balances
5. net radiation balance for Earth = 0
Land and Water Contrasts
a. Heating
1. a land surface heats up more rapidly and reaches a higher
temperature than a comparable water surface subject to the same
insolation
2. reasons
a. Specific Heat
1) specific heat of water is 5 times as great as that of land
a) specific heat: amount of energy required to raise temperature
of 1 gram of a substance 1oC
b) water can absorb more solar energy without its temperature increasing
b. Transmission
1) water is a better transmitter of radiation than land
a) sun rays penetrate water more deeply
b) heat diffused over a larger volume of water
c. Mobility
1) in water turbulent mixing and ocean currents (convection) disperse
heat more broadly and deeply
2) heat in land is dispersed only by conduction, and land is a very
poor conductor
d. Evaporative Cooling
1) evaporation much more prevalent over water
2) the requisite latent heat for evaporation is drawn from the water, dropping
the temperature
b. Cooling
a. a land surface cools more rapidly and to a lower temperature than a
water surface when both are overlain by air at the same temperature
c. Implications
a. both the hottest and the coldest places on Earth are found in the
interiors of continents
Chapter 4: Insolation and Temperature – p. 9 of 14
X.
b. a continental climate experiences greater seasonal extremes of
temperatures than a maritime climate
1) summers are hotter; winters are colder
2) compare San Diego and Dallas, Fig 4-24
a) same latitude
b) annual average temperatures are almost the same
c) monthly average temperatures vary significantly
c. oceans act as great reservoirs of heat, moderating temperature
extremes
d. greater latitudinal temperature ranges in the Northern Hemisphere
than in the Southern Hemisphere because more land surface in the
Northern Hemisphere (39% v. 19%)
Mechanisms of Heat Transfer
A. Intro
1. atmospheric and ocean circulation  persistent shifting of warmth
from the low latitudes toward the high latitudes
a. moderates the buildup of heat in equatorial regions
b. moderates the loss of heat in the polar regions
B. Atmospheric Circulation
1. 75-80% of all horizontal heat transfer is accomplished by atmospheric
circulation
2. discussed Chapter 5
C. Oceanic Circulation
1. Intro
a. currents: oceanic water movements
b. relationship between general circulation patterns of the atmosphere
and oceans
1) air blowing over the surface of the water, wind, is the principal
force driving the major surface ocean currents
2) ocean currents reflect average wind conditions over a period of
several years
2. The Basic Pattern (Fig 4-25)
a. subtropical gyres: enormous, elliptical ocean current systems
centered on the oceanic subtropical high-pressure cells
1) centered in each ocean ~ 30oN and S, except Indian Ocean (where
it’s closer to equator)
2) flows clockwise in northern hemisphere; counterclockwise in
southern hemisphere
b. equatorial current
1) on equatorward side of each subtropical gyre at ~ 5 o – 10o N and S
2) flows westward
3) equatorial countercurrent
a) in between the equatorial currents, along the equator
b) flows eastward
c. general circulation:
Chapter 4: Insolation and Temperature – p. 10 of 14
1) equatorial current flows poleward along western margins of ocean
basins
2) currents flow eastward at the poleward margins of the ocean basins
3) currents then flow equatorward along eastern margins of the ocean
basins
d. forces driving currents:
1) impelled by wind
2) influenced by Coriolis effect, deflective force of Earth’s rotation
a) to right in northern hemisphere
b) to left in southern hemisphere
3. Northern and Southern Variations
a. little poleward flow in northern hemisphere makes it to the Arctic
Ocean due to proximity of continents
b. in North Atlantic a portion flows northward between Greenland and
Europe
c. west wind drift
1) one continuous flow in the southern hemisphere because of
lack of land masses
2) westward flow around globe at ~ 60oS
4. Current Temperatures
a. temperatures of the currents impact latitudinal heat transfer
b. current temperatures:
1) low latitude currents = warm water
2) poleward-moving currents along western margins of oceans
carry warm water toward higher latitudes
3) equatorward-moving currents on the eastern margins of ocean
basins carry cool water toward the equator
c. latitudinal heat transfer results from general circulation of oceans:
poleward flow of warm tropical water along the eastern coasts
of continents and an equatorward flow of cool high-latitude
water along the western coasts of continents
5. Western Intensification
a. poleward moving warm currents off the east coast of continents
tend to be narrower, deeper and faster than the equatorward
moving cool currents
b. cause: Coriolis effect
6. Rounding Out the Pattern
a. northern hemisphere oceans receive influx of cool water from the
Arctic Ocean
1) Labrador Current along Canada’s east coast
2) Kamchatka Current along Siberian coast to Japan
b. upwelling of cold water occurs where equatorward flowing cool
currents pull away from subtropical western coasts
1) resulting nutrient-rich surface water make west coast marine
ecosystems highly productive
2) Peru/Humboldt Current along South America’s western coast
Chapter 4: Insolation and Temperature – p. 11 of 14
XI.
3) California Current along North America’s western coast
4) Canaries Current along Africa’s northwestern coast
5) Benguela Current along Africa’s southwestern coast
c. global conveyor belt circulation: deep ocean circulation pattern
7. Focus: Measuring Sea Surface Temperature by Satellite
a. MODIS (Moderate Resolution Imaging Spectroradiometer) gathers
surface temperature data around the globe
b. sea surface temperature (SST) is one of the most important
influences of weather and climate
1) temperature of air masses
2) intensity of storms
c. global conveyor belt circulation: deep ocean circulation pattern
Vertical Temperature Patterns
A. Environmental Lapse Rate
1. typically a general decrease in temperature occurs with increasing
altitude throughout the troposphere
2. environmental lapse rate: observed trend of vertical temperature
change in the atmosphere
3. for air at rest
B. Average Lapse Rate
1. variable
2. average lapse rate = 3.6oF/1000 ft (6.5oC/km)
C. Temperature Inversions
1. temperature inversion: a situation in which temperature in the
troposphere increases with increasing altitude
a. most prominent exception to the average lapse rate condition
b. inhibits vertical air movement  increased air pollution
2. Surface Inversion
a. radiational inversion: surface inversion that results from rapid
radiational cooling of lower air, typically on cold winter nights
1) cold ground cools air above it by conduction
2) prevalent in high latitudes primarily during winter
b. advectional inversion: surface inversion that results from horizontal
inflow of cold air into an area
1) common along coasts where cool maritime air blows onto coast
2) any time of year
c. cold air drainage inversion: cooler air slides down a slope into a valley
1) common in winter in some midlatitude regions
3. Upper-Air Inversion
a. subsidence inversion: a temperature inversion that occurs well
above the Earth’s surface as a result of air sinking from above;
associated with high pressure conditions
b. base is usually a few hundred meters above the ground
c. occurrence:
1) northern hemisphere continents in winter
2) subtropical latitudes throughout the year
Chapter 4: Insolation and Temperature – p. 12 of 14
XII. Global Temperature Patterns
A. Intro
1. isotherms: lines joining points of equal temperature
2. global temperature patterns are shown with isothermal maps
3. temperature maps are based on monthly averages which are based on
daily averages (Figs 4-29 and 4-30)
B. Prominent Controls of Temperature
Gross patterns of temperature are controlled largely by the following four
factors:
1. Altitude
a. temperature responds sharply to altitudinal changes
b. maps displaying world temperature patterns often use data modified
by reducing temperature to what it would be if the station were at sea
level
2. Latitude
a. isotherms on world temperature maps have conspicuous eastwest trend
b. if earth had a uniform surface and did not rotate, isotherms probably
would coincide exactly with parallels, showing a progressive
decrease of temperature poleward form the equator
c. the fundamental cause of temperature variation the world over is
insolation, which is governed primarily by latitude
3. Land-Water Contrasts
a. summer temperatures are higher over the continents than over
the oceans; the isotherms over the continents bend poleward
b. winter temperatures are lower over the continents than over the
oceans; the isotherms over the continents bend equatorward
c. in both seasons isotherms make greater north-south shifts over
land than over water
d. regularity of isothermal pattern in the midlatitudes of the southern
hemisphere is a manifestation of the fact that there is very little land
4. Ocean Currents
a. isotherms in near-coastal areas of the oceans have prominent bends
where warm or cool currents reinforce the land-water contrast
b. cool currents deflect isotherms equatorward; warm currents
deflect them poleward
c. cool currents produce the greatest isothermal bends in the warm
season; warm currents in the cool season
C. Seasonal Patterns
1. isotherms reflect the changing balance of insolation: moving
northward from January to July and southward from July to
January
2. isothermal shift is more pronounced in high latitudes than low
latitudes and over continents than over the oceans
Chapter 4: Insolation and Temperature – p. 13 of 14
3. temperature gradient is steeper in winter than in summer
(reflected in more tightly packed isotherms) and over continents than
oceans
4. the coldest places on Earth are over landmasses in high latitudes
a. in January: Siberia, Canada, Greenland
b. in July: Antarctica
5. the highest temperatures are found over the continents in
subtropical latitudes where descending air maintains clear skies, not
in equatorial regions where frequent cloudiness precludes highest
temperatures
a. in July: northern Africa and southwestern Asia and North America
b. in January: Australia, southern Africa, South America
6. highest average annual temperatures are in equatorial regions
because these regions experience so little winter cooling
D. Annual Temperature Range (Fig 4-35)
1. average temperature range: difference between the average
temperatures of the warmest and coldest months (usually, but not
always, Jul and Jan)
2. largest annual temperature ranges occur in the interiors of high
latitude continents
3. annual temperature ranges in the tropics are very small
XIII. Global Warming and the Greenhouse Effect
A. “natural” greenhouse effect
1. basis of life on our planet
2. without it Earth would be a frozen mass, 54 o F colder than it is today
B. global warming
1. average global temperature increase of about 1.3oF during 20th
century; 0.4oF in last quarter of 20th century
2. last 2 decades hottest since widespread record keeping (140
years) – 8 of 10 hottest years on record have occurred since 2000
3. apparent cause is human enhanced greenhouse effect
4. as greenhouse gas concentrations in atmosphere increase, more
terrestrial radiation is retained in the lower atmosphere
5. increased concentration greenhouse gases:
1) carbon dioxide (CO2)
a) responsible for 64% of human-enhanced greenhouse effect
b) source: burning fossil fuels (coal, petroleum)
c) increased 30% since 1750
d) current 390 ppm (parts per million): greater than any other time
in past 800,000 years
2) methane from grazing livestock, rice paddies, combustion of fossil fuels;
doubled since 1750
3) nitrous oxide from fertilizer and automobile emissions (↑ 17%
since 1750)
4) chlorofluorocarbons (CFCs) from synthetic chemicals used as
refrigerants and propellants in spray cans
Chapter 4: Insolation and Temperature – p. 14 of 14
6. as CO2 has increased so have average global temperatures
7. increasing evidence that most of the warming observed over the
last 50 years is anthropogenic (human induced)
C. IPCC (Intergovernmental Panel on Climate Change) 2007 Fourth
Assessment Report:
1. “Warming of the climate system is unequivocal…”
2. “Most of the observed increase in globally average temperatures
since the mid-20th century is very likely [greater than 90%
probability] due to the observed increase in anthropogenic
greenhouse gas emissions.”