This document provides an overview of key concepts in climate science. It discusses how climate science aims to observe, interpret, and explain the interconnected climate system, which includes the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere. It also notes that climate science requires an integrative and interdisciplinary approach. The document then summarizes several important aspects of the climate system, including definitions of climate and weather; components and complexity of the climate system; natural climate variability mechanisms like ENSO, NAO, PDO, and AMO; climate forcings and feedbacks; and factors that influence climate like solar activity, volcanoes, and plate tectonics.

1. Key
Concepts
in Climate
Science
Data collection and
presentation by
Carl Denef
Januari 2014
*

2. The present slide show introduces
the reader to the main aspects of the
climate system and its natural variability.
The presentation relies on what Climate
Science has concluded from observed
data and theoretical models. Climate
Science is an integrative part of Earth
System Science that aims to observe,
interpret and explain the interconnection
and balance between the four main
Earth System domains: atmosphere,
land, water and life. Climate Science
requires the integrative participation of
all scientific disciplines, going from
physics, mathematics, geology,
chemistry, statistics and computer
sciences to biosciences, ecology,
economy, sociology and anthropology.
Climate Science is also related to human
behavior and ethical consciousness, as
human-induced climate change can have
serious negative impacts on human
prosperity and development, may
worsen inequality between people and
may trigger major conflicts.

3.  Climate is the long-term average
(at least 30 years) of the condition of
the atmosphere in terms of
temperature, humidity, atmospheric
pressure, wind and precipitation in a
given area. It represents a statistical
distribution of these conditions,
including the mean values and ranges.
 The weather is the average condition
of the various elements of the
atmosphere in a given area over
short periods.
 Statistically significant deviations from
the average condition are called
anomalies or departures.
 The climate system is an
interactive system consisting of 5
major components: the
atmosphere, the land surface, the
hydrosphere (oceans, seas, rivers,
lakes, aquifers), the cryosphere
(land ice sheets,
sea ice, glaciers, snow fields) and
the biosphere (living organisms,
dead organic matter).
 The climate system is complex
and chaotic. Various weather and
climate drivers and feedbacks
exist. Their magnitude and the
ways that these drivers and
feedbacks interact are not fully
predictable. Hence, climate
variation and climate change can
never be predicted with
absolute certainty. Usually,
predictions are formulated as a
range between upper and lower
values, with confidence limits and
uncertainty evaluations.
 The main drivers of climate are the
incoming energy from the Sun
and the reflection, absorption
and re-emission of energy within
the atmosphere, clouds and
surface.
The climate system

4. ◦ A climate in equilibrium is a
dynamic equilibrium. At the global
level total incoming energy is in
balance with the total energy
emitted to space, but not every
location on Earth is in energy
balance. The distribution of the net
radiation imbalances over the
globe are the origin of different
types of climate. Imbalance brings
the atmosphere and oceans into
motion. Most of the incoming
energy is captured in the tropics
and subtropics, and then
repartitioned to middle and high
latitudes by winds and ocean flows.
◦ Any variation in the factors that
affect incoming and/or outgoing
energy or that modify the energy
repartition, will affect climate. For
some parts of the climate system
the relationship between cause and
response seems linear; in other
cases this relationship is more
complex, characterized by
hysteresis, or non-additive
combination of feedbacks.
◦ Climate variability refers to
changes in the energy balance over
short time scales ranging from
seasonal and annual, to a few
decades. Some climate variations are
cyclic while others are based on
specific events, such as volcanic
eruptions.
o Climate change refers to a change
in the energy balance over time,
scales ranging from decades to
millions of years. Changes can be
worldwide or only affect a region or
a hemisphere. Responses may vary
between regions. Climate change
may also affect its variability and
weather extremes.

5. ◦ Various climate types are determined by lattitude, terrain, altitude, prevailing wind direction
and nearby mountains and seas.
Source

6. Natural climate variability
◦ In addressing climate change it is
essential to have insight into natural
climate variability. Trends in climate
change can then be distinguished more
accurately and studied in climate
models. Variability is often cyclic with a
typical periodicity of a few years or a
few decades. Variability may
temporarily exacerbate or mask climate
change.
◦ Climate variation can be seasonal or
non-seasonal. The 4 season cycles
(spring, summer, autumn and winter)
are typical for higher latitude regions,
while the cycles of rainy (monsoon)
and dry season are seen in tropical
regions.
◦ Several non-seasonal climate variations,
most of them being cyclic, have been
identified. Some will be shortly dealed
with in the next slides (in order of
importance):
:
• El Nino/Southern Oscillation
• North Atlantic Oscillation
• Pacific Decadal Oscillation
• Atlantic Multidecadal Oscillation

7. Seasons
◦ Seasons result from cyclic variations in the length of exposure to solar radiation, as a
consequence of the tilt (23.5°) of the Earth's axis relative to the plane of the Earth’s
orbit around the Sun. For a specified location the length of exposure (length of the
day) depends on the time in the year.
◦ The time of the year when day and night have identical durations at all points of the
World is called equinox. This occurs two times in a year: at the start of spring and at
the start of autumn. The boundary between the illuminated and dark half-globes then
passes through both Poles. The time of the year when daylight is longest on the
northern hemisphere, is called June solstice. The time of the year with the shortest
daylight in the northern hemisphere is called December solstice. The higher the
latitude, the longer the longest day and the shorter the shortest day. Within the Arctic
Circle daylight is all day long at the start of the summer and is absent at the start of
the winter. In the Southern hemisphere, there it is winter during the June Solstice.

8. El Nino Southern oscillation (ENSO)
◦ ENSO is an oscillating variations in sea surface temperature (SST) in the east-
central tropical Pacific Ocean (at least 0.5°C averaged over that region). A warming
is known as El Niño and cooling as La Niña. This anomaly happens at intervals of 2-7
years, and lasts 9 months to 2 years.[5] El Niño is Spanish for "the child", and refers
to Jesus, because initiation of warming in the eastern Pacific occurs usually around
Christmas.[4]
◦ During El Niño SST is generally 1.5-2.5oC above average (up to 29 °C). In the
subsurface (~100 m depth) ocean temperatures typically is 3o-6o above average.
During La Niña SST is generally 1o-2oC and sub-surface temperature typically 2o-4oC
below average.
◦ The fluctuations in ocean temperatures are accompanied by even larger fluctuations in
air pressure between Darwin, Australia (western Pacific) and Tahiti (central-
eastern Pacific). Low atmospheric pressure tends to occur over warm water and high
pressure occurs over cold water. During El Niño there is low atmospheric pressure over
Tahiti, and this is accompanied by high atmospheric pressure over Darwin, Australia,
while La Niña displays high pressure in the eastern Pacific, accompanied by low
pressure in the western Pacific.[2][3]
◦ The pressure differences strongly affect the Pacific trade winds (dominant winds that
blow from east to west (easterly winds)). El Niño weakens the strength of the trade
winds in the eastern Pacific, and reverses the trade winds in the western Pacific. Trade
winds intensify during La Niña, due to the higher atmospheric pressure over the eastern
Pacific, forcing an abnormal accumulation of cold water into the central and eastern
Pacific Ocean.

9. ◦ Trade winds move water warmed by the sun toward the west, which
creates upwelling of deep ocean off the coasts of Peru and Ecuador. This
brings nutrient-rich cold water to the surface, sustaining large fish
populations, which in turn provide abundant food to sea birds. El Niño
reduces the upwelling of this nutrient-rich water, leading to fish kills off the
shore of Peru with serious negative socio-economic impacts.[7]
Low
pressure

10. Normal
El Niño
High
pressure
La NiñaLow
pressure

11. The strength of ENSO is quantified by the SST index and by the Southern
Oscillation Index (SOI). SOI is computed from fluctuations in the surface air
pressure difference between Tahiti and Darwin, Australia. [8] El Niño episodes are
associated with negative values of the SOI, meaning there is below normal
pressure over Tahiti and above normal pressure over Darwin (red color in Figure).
Positive values are typical for La Niña (blue color in Figure).
Notice the
domination of El
Niño in the 1990s
and of La Niña after
2000.
Source: Waish et al.
Polar Science 7,
188-203, june 2013
SSTdeparture°C
La Niña
El Niño
La Niña
El Niño

12. ◦ El Niño SST index is monitored in four regions along the equator:
Niño 1 (80°-90°W and 5°-10°S)
Niño 2 (80°-90°W and 0°-5°S)
Niño 3 (90°-150°W and 5°N-5°S)
Niño 4 (150°-160°E and 5°N-5°S)
Niño 3.4 (120°-150°W and 5°N-5°S): correlates better with the SOI and is the
prefered region to monitor SST.
Darwin, Australia
South-America
Look at an animation of the ENSO condition of the present year here (NOAA
Physical Oceanography Division).

13. ◦ During El Niño it rains more during the spring even in western Europe.
During La Niña the opposite occurs. These climate oscillations cause
extreme weather (floods and droughts) in many regions of the World. El
Niño and La Niña also have a strong effect on the Jet Stream (read more)
◦ El Niño of 1982-83 brought extreme warming to the tropical Pacific. SST in
some regions rose 6° C above normal. The warmer waters had a
devastating effect on marine life off the coast of Peru and Ecuador. Fish
catches were 50% lower than the previous year. The 1982-83 El Niño also
had a pronounced influence on weather in the equatorial Pacific region and
World wide. Severe droughts occurred in Australia, Indonesia, India and
southern Africa. Dry conditions in Australia resulted in a 2 billion dollars
loss in crops, and millions of sheep and cattle died. Heavy rains were
experienced in California, Ecuador, and the Gulf of Mexico.
◦ What is suprising, however, is that the changes in SST are usually not
large, plus or minus 3°C and generally much less, and yet, these minor
changes can have large effects on global weather patterns and the
biosphere.

14. The Pacific decadal oscillation (PDO)
◦ The PDO is a pattern of change of sea surface temperature in the Pacific
Ocean north of 20° N. The PDO is detected as warm or cool surface waters.
During a "warm", or "positive", phase, the west Pacific becomes cool and part of
the eastern ocean warms; during a "cool" or "negative" phase, the opposite
pattern occurs. It shifts phases on a time scale of about 20 to 30 years.
Observed monthly values for the
PDO (1900–feb2013).

15. North Atlantic Oscillation (NAO)
◦ NAO is a climate variation without periodicity in the North Atlantic Ocean,
consisting of fluctuations of the difference in atmospheric pressure between
the Iceland low and the Azores high pressure zones. The relative strengths
and positions of these pressure zones oscillate in an east-west motion. A large
pressure difference at the two locations is denoted as a high index NAO year
(NAO+) and leads to increased westerly winds and, consequently, cool summers,
and mild and wet winters in Central Europe and the Atlantic coast. If the index is
low (NAO-), westerlies are suppressed, and these areas suffer more extreme
climate (heat waves, deep freezes and reduced rainfall) and storm tracks toward
southern Europe and North Africa.
The frequent negative NAO index values in the sixties coincide with the very cold
winters in Europe at that time. The winter of 2009-10 in Europe was unusually cold
which coincided with an exceptionally negative phase of NAO.[11] The very positive
values in the late 80-ties up to 1995 corelate with very mild winters in that period.
Source

16. The Atlantic Multidecadal Oscillation (AMO)
◦ AMO is a cyclic variability in the sea surface temperature occurring in the North
Atlantic Ocean. Instruments have observed AMO cycles only for the last 150
years. However, palaeoclimate studies of tree rings and ice cores, have shown that
oscillations similar to those observed instrumentally have occurred for at least the
last 1000 years.
◦ The AMO has affected air temperatures and rainfall over much of the Northern
Hemisphere, in particular North America and Europe. It is associated with changes
in the frequency of North American droughts and severe Atlantic hurricanes.
◦ Read more here (NOAA)

17. Climate forcings and feedbacks
◦ Climate can change through two categories of processes:
◦ Climate forcings: processes that are the primary drivers of climate
change
◦ Climate feedbacks: processes that can either amplify or diminish the
effects of climate forcing. A feedback that increases an initial change is
called a "positive feedback”. A feedback that reduces an initial change is a
"negative feedback".
Climate forcings
Internal forcing
• Life processes
• Thermohaline circulation
• Tectonic plate activities
External forcing
•Total solar irradiance
• Cosmic ray irradiance
• Variations in the Earth’s orbit
• Radiative forcing
• Aerosols, dust, smoke, and soot
Climate feedbacks
• Cloud-albedo
• Ice-albedo
• Land use changes

18. Climate forcing
◦ Life processes: Changes in plant mass distribution can force climate change, since
plants use CO2 and CO2 is the principal natural greenhouse gas that determines the
temperature of the atmosphere at the Earth’s surface. An example of biological forcing
is the ‘Azolla event’ (see Palaeoclimate)
◦ Thermohaline circulation in the oceans. Thermohaline is derived from ‘thermo’ -
referring to temperature and ‘haline’ - referring to salt content of oceans, factors which
determine the density of sea water. Wind-driven surface water currents (such as the
Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and
eventually sinking at high latitudes as a consequence of wind-driven evaporation which
makes the water more salty and cooler and hence more dense. This dense water then
flows over the ocean basins to the Southern Oceans where Antarctic ice-cooled water
sinks down. Because of these sinking cold waters, there must be water upwelling
elsewhere. Thermohaline circulation causes extensive mixing between the
ocean basins. The water masses transport heat around the globe which has a
potential impact on climate. For example, in the North Atlantic, the northward flowing
warm surface currents, including the Gulf Stream, provide heat of >1000 terrawatt to
NW-Europe, which is equivalent to the energy output from more than one million 1-
Gigawatt nuclear power plants.
The oldest waters have a transit time of around 2000 years. This ‘slow’ circulation
nevertheless moves and mixes 900,000 Gigatons of water per year, equivalent to 30
times the global river flow. This ‘ocean conveyor belt’ also transports many Gigatons of
carbon and nutrients which are vital for life. [Ref]

19. Thermohaline circulation
Source

20. ◦ Plate tectonics. The outer layer of the Earth (the lithosphere) is broken into
pieces, called tectonic plates, that move in relation to one another at a rate of
about 3 cm per year. Over the course of millions of years, this motion
configures where land and ocean are located on the globe (continental drift). The
locations of land and sea affect the transfer of heat and moisture across the
globe, and the location of land will affect the heat captured from the Sun, in this
way determining climate. Continents warm at rates different from that of oceans,
which determines global wind patterns .
When landmasses are concentrated near the polar regions, there is an increased
chance for snow and ice to accumulate on land. Small changes in solar energy
can then tip the balance between summers in which the winter snow mass
completely melts and summers in which the winter snow persists until the
following winter. The presence of snow and ice strongly increases albedo
(surface reflectivity of solar radiation), resulting in cooling.
Uplift of land masses (for example of Himalayas by the Indian plate) leads to
major weathering and sequestration of CO2 as carbonate in rocks
◦ Solar radiation
Solar radiation is the source of heat for the Earth. The Sun emits X-rays,
ultraviolet (UV), visible light, infrared, and even radio waves, spanning a range
of 100 nm to 1 mm waves.

21. Solar radiation at the top of the atmosphere is composed of ~ 50% infrared light
(700 nm -1 mm), ~ 40% visible light (380-780 nm), and ~ 10% UV (100-380 nm).[3]
At ground level it is ~ 53% infrared, ~ 44% visible light and ~ 3% UV.[4]
Total solar radiation (or irradiance) (TSI) at the top of the atmosphere is the
amount of solar energy incident on an area with the Earth’s diameter and perpendicular
to the rays. It is expressed in Watt (W)/m2 (the so called ‘solar constant’). At
present, TSI = 1361 W/m2. However, taking into account that the Earths surface is a
globe and that at any one moment half the planet does not receive any solar radiation,
average solar radiation at the top of the atmosphere = ~ 340 W/m2. This value has
been confirmed by recent SORCE/TIM satellite measurements (see IPCC- AR5 chap. 2).
There are cyclic variations in TSI with different periods.
1. The 11-years sunspot cycles[31]. There is 0.1% variation in the sun’s
energy output with an average cycle of ~ 11 years, due to a cyclic expansion of
the number of what is called ‘sunspots’. Sunspots are magnetic regions on the
Sun surface with magnetic field strengths thousands of times stronger than the
Earth's magnetic field. They are darker (emit less energy) than the surrounding
area, but the surrounding margins - called faculae - are much brighter, resulting
in more solar irradiation when sunspots are more numerous. A Sunspot typically
lasts only for several days, but it is their average number that shows cyclic
variation. Sunspots cycles have been studied and measured for several hundreds
of years. Since 1979 changes in radiation have also been measured by satellites. It
was found that the number of sunspots correlates with the intensity of

22. solar radiation. For the period 2001–2010, about 124 W/m2 of TSI was reflected by
clouds, atmosphere and surface and 79 W was absorbed by the atmosphere (see IPCC-
AR5 chap. 2). Therefore, global average TSI at the Earth’s surface = ~160
W/m². Thus, averaged over the globe, sunspot variation theoretically
represents only ~0.16 W/m2 at the Earth’s surface.
2. Centennial cycles. As far as based on palaeoclimate reconstruction studies using
cosmogenic radionuclides as proxies*, TSI shows cycles of 88 years (Gleisberg
cycle), 208 years (DeVries cycle) and 1,000 years (Eddy cycle).
3. At a time scale of tens to thousands of years there are fluctuations of TSI that
are associated with changes in the solar magnetic field. Evidence of variations in solar
activity with this timescale can be found in the records of cosmogenic radionuclides.
* Proxies are preserved physical characteristics of the past that are in close
correlation with the climatic conditions that prevailed during much of the Earth's
history. Changes in their quantity allows reconstruction of climate changes up to
500 million years ago. Examples are: ice cores, relative quantities of particular
isotopes, cosmogenic radionulides, tree rings, sub-fossil pollen, boreholes, corals,
and lake and ocean sediments. Read more in the ‘Palaeoclimate’ section.
◦ Cosmic ray irradiance. Cosmic rays may be indirectly implicated in climate change
because they produce ionized particles upon passage in the atmosphere that could
serve as condensation centers of cloud formation. Clouds enhance Earth’s reflectivity
of solar radiation and in this way result in surface cooling.

23. ◦ Variations in the Earth’s orbit. The Earth’s orbit around the Sun is an ellipse.
The Sun is positioned in one of the focal points. There are three variable
components in this orbit: eccentricity, the axial tilt angle of the Earth's axis of
rotation, and precession of the Earth's axis (see Figures in next slides and
animations). These orbital alterations are known as Milankovitch cycles.
SEE ANIMATIONS
Eccentricity (or ellipticity) is expressed as % deviation from a circular orbit around
the Sun. The maximum ellipticity is 6 %, the minimal 0.5 % (near circular orbit)
and, at present, is 1.7 %. The distance of the Earth to the Sun determines the
amount of energy received. It changes with the position of the globe on its orbit.
At present, the closest distance (perihelion) is reached around January 3, the
largest (aphelion) around July 4.
At present, the difference in TSI between perihelium and aphelion is 92
W/m² or a ~7 % difference in energy delivery (from Wikipedia). This is almost
an order of magnitude higher than the difference in maximum and minimum TSI
within the 11 year solar cycles today.
The eccentricity varies in cycles with periods of ~100,000 and ~413,000 years due
to the gravitational influence of the Moon and other planets.

24. When the Earth’s orbit is at its most elliptical, the Earth in Perihelium is at
its most closest to the Sun and, thus, will receive more heating at that
position than when the orbit is at its most-circular. Thus, the level of
eccentricity will affect climate.
The 100,000-year eccentricity cycle corelates with the Ice Age cycles during
the last million years, suggesting that solar forcing is the dominant forcing
signal.
Circular orbit, no
eccentricity.
Elliptic orbit with
50% eccentricity.

25. Tilt angle is the angle between the Earth’s rotational axis
and the axis of its orbit around the Sun. It slowly changes
between 22.1° and 24.5° and back again, taking
approximately 41,000 years to shift. When tilt increases,
the amplitude of the seasonal differences in solar irradiation
increases, with summers in both hemispheres receiving more
radiative flux, and winters less. Conversely, when tilt
decreases, summers receive less and winters more.
22.1–24.5° range of
Earth's tilt
See animation
Importantly, these changes are not of the same magnitude everywhere on the
Earth's surface. At high latitude the annual mean irradiation increases with
increasing tilt, while lower latitudes experience a reduction in irradiation.
Cooler summers are expected of facilitating the onset of an Ice Age, due to less
melting of the previous winter's frozen precipitation. Currently the Earth is
tilted at 23.44°, roughly halfway between its extreme values. The tilt is in the
decreasing phase of its cycle, and will reach its minimum value around the year
11,800 . This tends to make winters warmer and summers colder (i.e. milder
seasons), and cause an overall global cooling.
Because changes in winter and summer compensate for each other, the change
in the annual average insolation at any given location is near zero, but the
redistribution of energy between summer and winter strongly affects the
intensity of seasonal variation. Such redistribution changes are considered a
likely cause for the coming and going of recent Ice Ages.

26. Precession is a slow and continuous change in the orientation
of the Earth’s rotational axis as referred to a fixed star (at
present the North star). It is caused by tidal forces exerted by
the Sun and the Moon’s gravity on the Earth’s equator. A full
precession cycle has periods ranging between 19,000 to 24,000
years.
Effect on climate: When the Earth’s rotation axis points toward
the Sun when the Earth is in perihelion, the northern
hemisphere has a greater difference between the seasons while
the southern hemisphere has milder seasons. When the axis
points away from the Sun in perihelion, the southern
hemisphere has a greater difference between the seasons while
the northern hemisphere has milder seasons.
Precession
See animation
See animation of
a spinning top
The 100,000-year eccentricity cycle corelates with the Ice Age cycles during
the last million years, suggesting that solar forcing is the dominant forcing
signal. However, there is one problem: when tested by climate models the
eccentricity variations have a significantly smaller impact on solar forcing than
forcing by precession or tilt changes. Climate change is much more intense
than the solar irradiance alone can explain. Therefore, various internal
characteristics of the climate system are believed to be sensitive to the
irradiation changes, which in turn amplify (positive feedback) or damp
responses (negative feedback). See next slide.

27. ◦ Radiative forcing. Radiative forcing is a measure of the disruption a factor has
on the balance of incoming and outgoing energy in the Earth’s atmosphere and
is expressed in W/m2. It is caused by an increase of greenhouse gas levels
above the natural flux. In the context of climate change, radiative forcing is
restricted to the near-surface troposphere.
◦ Greenhouse gases are water vapor, clouds, CO2, methane (CH4),
nitrous oxide (N20), ozone (O3) and human-made halocarbons. The
Earth’s surface absorbs the shortwave radiation (= visible, near-ultraviolet,
and near-infrared waves) of the Sun and reflect a part back upward as
longwave infrared radiation. Greenhouse gases absorb certain wavelengths
of the long wave infrared light emitted by the Earth’s surface, which causes
tropospheric heating, and then re-radiate it as longwave radiation (from
0.7μm to 5.0μm) in all directions, which causes additional warming of the
troposphere (positive forcing). In addition, pollutants, such as CO, nitrogen
oxides and SO2, enhance the greenhouse effect by altering the abundance of
CH4 and ozone.

28. ◦ Aerosols, dust, smoke, and ‘black carbon’ (soot). These are very small
particles suspended in the atmosphere. Sulfate aerosols are generated by
burning coal and biomass and are present in volcanic eruptions. They
tend to cool the Earth (negative forcing) because they absorb, scatter and
reflect solar radiation. Other kinds of particles such as black carbon have
a positive forcing by absorbing radiation and re-emitting it as longwave
infrared light. Indirectly, aerosols also affect cloud albedo, because many
aerosols serve as cloud condensation nuclei (CCN) or ice nuclei, which are
initiators of cloud or ice formation. Changes in particle types and
distribution can result in small but important changes in cloud albedo (see
next slide). The global distribution of aerosols is being tracked from the
ground and from satellites.

29. Climate feedbacks
◦ Cloud-albedo. Albedo of an object is the reflective capacity that object has on
solar radiation. Clouds reflect ~1/3 of the sunlight back into space. Even small
changes in the extent of clouds, their location and type have large consequences.
Climate warming causes more water to evaporate, leading to an increase in
cloudiness, which results in a cooling effect. On the other hand, water vapor and
clouds are greenhouse gases causing warming. The net effect on surface
temperature will depend on the cloud type and characteristics, the cloud height,
and the nature of cloud condensation nuclei. Thin high clouds (height >6 km,
paricularly cirrus clouds in the stratosphere) generally generate net heating, and
thick low clouds (altitudes below 2 km) produce a cooling.
◦ Ice-albedo. Ice is white and very reflective, in contrast to the ocean surface,
which is dark and absorbs more heat. As the atmosphere warms and sea ice
melts, the darker ocean absorbs more heat, causes more ice to melt, and makes
the Earth warmer overall. The ice-albedo feedback is a very strong feedback. The
Earth's average surface is currently ~15 °C. If the Earth was frozen entirely, the
average temperature would drop below −40 °C.[10] If all the ice on Earth were to
melt, the average temperature on the Planet would rise to ~27 °C.[12]
◦ Land use changes. Land use changes by conversion of forests to agriculture,
change the characteristics of vegetation, including its colour, seasonal growth and
carbon content, which in turn affect CO2 flux and land-albedo.

30. Solar forcing vs climate feedbacks
◦ The 100,000-year eccentricity cycles corelate with the Ice Age cycles during
the last million years, suggesting that solar forcing is the dominant forcing
signal. However, when tested by climate models the eccentricity variations
have a significantly smaller impact on solar forcing than forcing by
precession or tilt changes. Climate change is much more intense than the
solar irradiance alone can explain. Therefore, various internal
characteristics of the climate system are believed to be sensitive to the
irradiation changes, which in turn amplify (positive feedback) or damp
responses (negative feedback). See ‘Climate change’ slides.

31. FORCINGS AND FEEDBACKS IN THE CLIMATE SYSTEM

Black
carbo
nLW
R
SWR=shortwave radiation
LWR=longwave radiation
From IPCC AR5 (adapted)OVERVIEW