The Earth’s climate is dynamic and characterised by trends, aberrations and quasi-periodic oscillations varying over a broad range of time-scales [1], which are governed by external (extraterrestrial systems) and/or internal(ocean, atmosphere and land system). Trends are largely controlled by plate tectonics, and thus to change gradually on million year time scale. Aberrations occur when the certain thresholds are passed and are manifested in the geological record as the unusual rapid (less than a few thousands of years) or extreme change in climate. The quasi-periodic oscillations are mostly astronomically paced; they are driven by astronomical perturbations that affect the earth’s orbit around the sun and the orientation of earth’s rotation axis with respect to its orbital plane. These perturbations are described by the three main astronomical cycles: eccentricity, precession and obliquity, which together determine the spatial and seasonal pattern of insolation received by the earth [2], eventually resulting in climatic oscillations of ten to hundreds of thousands of year [3].Sun being the main source of energy for the earth system controls the climate of it. Variation in solar activity and cosmic ray intensity has direct influence over climatic features such as cloudiness, temperature and rainfall [4]. Volcanic eruptions also force all elements of the climatic systems up to a varying degree but producing long term climatic signals in the ocean. The cumulative volcanic cooling effect at present offsets about one third of anthropogenic warming [5].Other than these causes paleoclimatologists also relates the past climate changes with movement of solar system[6], interplanetary dusts and influence of asteroids[7].However the recent variability in climate what earth is experiencing is unlikely due to any of the individual above factors rather it is due to the compound effect of complex interactions of all the natural as well as anthropogenic forcings. References: 1. J. C. Zachos, M. Pagani, L. Sloan, E. Thomas, K. Billups, Science 292 (2001) 686-693. 2. G. Kukla, Nature (London) 253, 600 (1975). 3. J. D. Hays, J. Imbrie, N. J. Shackleton, Science 194 (1876) 1121-1132. 4. N. Marsh, H. Swensmark, Space Sci. Rev. 94 (2000) 215-230. 5. T. L. Delworth, V. Ramaswamy, G. L. Stenchikov, Geophys. Res. Lett. 32 (2005) L24709. 6. K. Fuhrer, E. W. Wolf, S. J. Johnsen, J. Geophys. Res. 104(D24) (1999) 31043-31052 7. P. Hut, W. Alvarez, W. P. Elder, T. Hansen, E. G. Kauffman, G. Keller, E. M. Shoemaker & P. R. Weissman, Nature Vol. 329, 10 September, 1987

4. Natural causes of climate
change
Debasish Chakraborty
Roll No - 4843
Division of Agricultural
Physics

5. Climate Variability
Inherent characteristics of earth’s climate which manifests itself
in changes of climate with time
Climate Change
It refers to the statistically significant variation in either the mean
state of the climate or in its variability persisting to an extended
period
It is mainly influenced by Natural factors and nowadays it is
speeded up by the Anthropogenic factors

6. Solar
Output
Earth-Sun
Geometry
Interstellar Dust
Earth’s Internal
Volcanic
Eruption
Mountain Building
Continental Drift
Atmosphere-Ocean Heat
Exchange
Atmospheric Chemistry
Natural Factors Influencing Earth’s Climate
Extraterrestrial

7. Earth-Sun Geometry
Motion Return Period Effect
Rotation 24 Hours Day - Night
Revolution 365.25 Days Seasons
Axial Tilt 41,000 Years Season, Shifting of
tropical & polar belts
Eccentricity 100,000 Years Seasonal Extremities
Precession 23,000 Years
Shifting of Solstices
& Equinoxes
Wandering of Poles
Chandler’s Motion

8. The Astronomical causes
The Milankovitch Theory (1924):
Johannes Kepler (1571 – 1630):
Earth has elliptical orbit path around the Sun
Joseph Alphonse Adhemer (1842):
Precession cycles , alternate hemisphere
James Croll
Curve of eccentricity, Winter temperature main for
Glaciations and Positive Feedback mechanism
Discovered and computed relationship
between Earth’s orbital parameters
(Precession, obliquity & eccentricity) and solar
radiation
Summer insolation in the polar latitudes
is the main cause of glaciation

9. Eccentricity
 Controls the shape of the Earth’s orbit
 Eccentricity(e)= (a2
– b2
)½
/a2
 The difference in between the perihelion & aphelion is 3% and
responsible for 7% variation in Solar radiation on the earth
 It varies from about
0.0669 to 0.0001
 Earth is now experiencing a
lower eccentricity of about
0.0167.
 The total cycle takes about
100,000 years

10. Precession
Cyclical variation of the earth’s rotation
around it’s polar axis
By this the timing of equinoxes and solstices
changes, so sometimes it is called ‘Precession
of Equinoxes’
‘Precession of Equinoxes’ has a
cycle of approximately 23,000 years
Is our pole or North star constant?
Now our pole star is ‘POLARIS’ But
around 2500 BC in the time of
Pyramids it was ‘THUBAN’ or ‘ALPHA
DRACONIS’.

11. Precession
• Now in the time of perihelion
Southern Hemisphere is closer
to the Sun
• Southern Hemisphere
summer receives 4% more
solar radiation than Northern
Hemisphere.
• After 11,000 years Northern
Hemisphere will be closer to
the Sun in the time of
perihelion

12. Obliquity or Axial Tilt
 It is the cyclical variation of
the Earth’s tilt of polar axis
 This tilt can deviate from
22.10
to 24.50
 At present the tilt is
23.440
and it is decreasing
 The Obliquity or Axial Tilt
cycle takes about 41,000
years

13.  When the Tilt is small there is less climatic variation between the summer
and winter seasons in the middle and high latitudes.
 Warmer winters allow for more snow to fall in the high latitude regions
 Cooler summers cause snow and ice to accumulate on the Earth's surface
because less of this frozen water is melted
 So the net effect of a Smaller Tilt would be more extensive formation of
glaciers in the polar latitudes.
Obliquity or Axial Tilt

14. Milankovitch Cycle and Glaciations
Core Selection
 Contains continuous climatic record and fast accumulation rates
 Located between Africa, Australia and Antarctica to avoid the
influence by variation of erosion from the continents
Geological Data
The Oxygen isotopic composition (δ 18
O)
Estimate of summer sea surface temperature at the core site(Ts)
Percentage of Cycladophora davisiana

15. Orbital Data
 The orbital and insolation changes was calculated using numerical
procedure
Chronological Models
 For testing the orbital theory ,age models must be developed to
express each geological variable as a function of time
SIMPLEX- Age is estimated as an exact linear function of depth
ELBOW- More chronological information and is not expressed as a
simple function of depth
PATCH- Time series where the records of two cores at the 8 – 7 stage
boundary was joined to provide longer and statistically more useful
records

16. Fig; Variations in obliquity, precession, and the corresponding frequency components of
climate over the past 500,000 years

17. Fig; Variation in eccentricity and climate over the past
500,000years
Conclusions:
Climate variances is concentrated
in three discrete peaks at periods of
23K,42K and 100K years
These peaks correspond to the
dominant period of the earth’s
orbit & contain 10,25 and 50
percent of the climatic variances
The changes in the Earth’s
orbital geometry are the
‘Fundamental causes of the
succession of ice ages’

18. Continental Drift-Theory of plate Tectonics
Motion in earth's asthenosphere which causes
global scale dynamics of the rigid lithospheric plates
Different Mechanisms:
Plates moves at an average rate of 3 cm per year

19. Evolution of present continental conformation

20. Altering the Distribution of Land Masses
Changing Continental Elevation
Variability in Atmospheric Concentration of
CO2
Major
Factors ofMajor Effects of Plate Tectonics

21.  Thermal Inertia:
Oceans have a higher thermal heat capacity than land.
 High Latitude Land Area:
More glaciers over land, higher albedo, cooler temperature
 Surface Albedo:
Amount of ocean versus land surface at low latitudes:
great affect of absorbed solar energy or reflection
Altering the Distribution of Land Masses:

22.  Restrictions to Ocean Currents:
Oceanic circulation is primary mechanism by which heat is
redistributed from equatorial to polar latitudes.
Continental barrier blocks the oceanic circulation & thus
creates problems to redistribution of heat throughout the globe.
Cretaceous warming
T.H. van Andel, "New Views on an Old Planet, a history of global change", Cambridge (1994)4

23. Changing Continental Elevation
 Change in Elevation or Mountain Building:
Atmospheric temperatures decrease with increase in height
(6.5°C per km).
High elevation leads to cold temperatures which ultimately
produces snow coverage & high albedo situation.
Even today the Himalayan range is rising by about 1mm/year as
Indian plate slowly moves towards the Eurasian plate.
 Atmospheric circulation:
Wind belts of the earth are influenced by pressure differences across
mountain chains.
A change in topography may alter the distribution of air masses.
 Regional Climate:
Different climate in different sides of the mountain

24. Variability in Atmospheric Concentration of CO2
Atmospheric carbon dioxide is released in the process of
weathering of minerals .
Weathering of minerals is accelerated by
Higher temperature & Collision of Continents
Carbon dioxide is released through
Drifting of the Continents(Mountain Building)
Volcanic Activity

25. Volcanoes
VEI 0 1 2 3 4 5 6 7 8
Eject
Volume
<10,00
0 m3
>10,0
00 m3
>1,000,
000 m3
>10,000,
000 m3
>0.1 km3 >1
Km3
>10
Km3
>100
Km3
>1000
Km3
Plume <100 m 1 Km 5 Km 15 Km 25 Km >25
Km
>25
Km
>25
Km
>25
Km
Example Mauna
Loa
Strom
boli
Galeras
(1993)
Cordon
Caulle
(1921
Eyjafjallaj
okull
(2010)
Mt.
St.
Helne
s
(1980
)
Mt.
Pinat
ubo
1991
Tambo
ra
(1815)
Taup
o
(26,5
00
BP)
Frequency many Many 3477 868 421 166 51 5 0

26. Volcanic Eruption:
Influence of Volcanoes
Very Short Term
Volcanic ash
Short Term Mid to Long Term
Aerosol
Atmospheric Circulation
Hydrological Cycle
Ocean
Scientists belief that volcanoes are having profound effect on
climate. But these effects are time dependent.

27.  These ashes lasts for few months
 Blocks the penetration of sunlight
into the atmosphere
 Tropospheric temperature drops
down
Volcanic ash

28. Net Radiative
Balance = -3 W/m2
Decrease in Global
Surface Air Temp.= 0.5
K
Global Visible
Optical Depth
Maximizes to 0.15
Mount Pinatubo,1991

29. Hydrological
Cycle
Precipitation is more sensitive to variation in solar SW
radiation
Precipitation drops
over land in 1st year
due to rapid radiative
cooling
But the precipitation over
ocean are delayed & maximum
reduced after 3-4 years of
eruption
Geographically the precipitation anomalies are located in
low latitude monsoon region

30. Atmospheric Circulation
 In the 2nd
year following eruptions, the NH winter tropospheric
circulation has typically been observed to display features of an
anomalously positive AO situation
 The Zonal mean expression is the creation of Low pressure at the
high latitudes & High pressure at the Mid latitudes i. e. North Atlantic
and Mediterranean sectors (North Atlantic Oscillation)
 Pole ward shift of Atlantic storm track & an increased flow of
warm air to Northern Europe and Asia where anomalously higher
winter temperature is observed
 Only low latitude volcanic eruptions could effect the AO/NAO phase
Stenchikov, Hamilton,Ramaswamy, 2003

31. Ocean
 Ocean Comprises almost the entire thermal capacity of the
climate system. Their thermal inertia delays full scale response of
the earth’s surface temperature to greenhouse warming
 Ocean warming cause expansion of water and therefore effects
the sea level, called thermosteric height
 The maximum Heat content and Sea level decrease after Pinatubo
eruption is 5 * 10 22
J & 9 mm respectively
Stenchikov et. al. (2007)
 The characteristics e-folding time for ocean heat content or
steric height is about 40 – 50 years and complete relaxation
requires 2-3 relaxation times

32. Oceanic Circulation
 SW cooling from volcanic aerosols results in a cold surface temperature
anomaly
 Volcanically induced cooling leads to reduced precipitation and river
run-off in High latitudes of Northern Hemisphere
 So, upper ocean condition in the higher latitudes of the northern
hemisphere becomes saline (denser)
 Colder ocean temperature & enhanced salinity destabilizes the water
column , making them more prone to ocean convection which in turn
enhances the MOC (Meridional Overturning Circulation)
 The maximum increase in MOC is 1.8 sverdrups or 9%

33. Solar Activity and Climate
 Solar activity and cosmic ray is negatively correlated
 There is a strong correlation between the previous cold and warm
climatic periods & high and low levels of cosmic ray intensity

34. Cosmic Rays and Cloud Cover
 Clouds effect the irradiative properties of the atmosphere by
both cooling through reflection of incoming SW solar radiation
and heating through trapping of outgoing LW radiation
 High optically thin cloud tend to heat and low optically thick
cloud tend to cool the atmosphere

35. Increasing Cosmic Ray intensity leads to increase
in the low level cloud coverage which ultimately
reduces the surface temperature.
> 6.5 Km
< 3.2 Km
6.5 – 3.2 Km

36. Cosmic Ray & Rainfall
 The Cosmic Ray intensity is directly proportional to the rate of ion
generation over the mid latitudes
 The Rate of ion generation is highly correlated to the total
surface of cloud cover with a correlation coefficient of 0.91 .
 Stozhkov analyzed 70 events of Forbush decrease of CR
intensity observed in 1956-1993 & compared this event with the
rainfall data over USSR. He showed that the daily rainfall levels
decreases by 17%.

37. Cosmic Ray & The Earth’s
Temperature
 Swensmark showed
that the increase of air
temperature by 0.30
c
corresponds to a
decrease of CR intensity
of 3.5%.
 This Decrease in
CR intensity reduces
the global cloudiness
by 3%, equivalent to
an increase of solar
irradiance by 1.5
W/m2
 This change in irradiance is 5 times bigger than the solar cycle
irradiance change (0.3 W/m2
)

38. Forecasting of Climate Change by Cosmic
RayRays
 CR intensity predicted
on the basis of monthly
Sunspot numbers from
model of Convection-
Diffusion & Drift
mechanism.
 The correlation
coefficient is 0.97.

39. Earth’s Climate and movement of solar system
 Paleoenvironmental records suggests that in the last 520 M years
Earth has gone through four alternating warming and cooling periods
with temperature change more than 50
c
 During this periods the Solar system crossed galaxy arms four times
 In this time inflow of comets from Oort’s cloud occurs, which results
in an increase in concentration of interplanetary dusts in Zodiac cloud
and cools earth’s climate
Fuhrer, Wolff, Johnsen, 1999

40. Earth’s Climate and Comet
 Comet in past have struck the Earth with huge force to make
major changes in the Earth’s climate (the famous Dinosaurs killing
mass extinction at the end of the cretaceous)
 The study published in
‘New Scientists’ journal’
tells us a step forward
that the comet struck the
earth near India & is the
main cause for extinction
of Dinosaur

41. IPCC WG1 AR4
Observed Changes
and Future Prediction
 Natural factors leading to
a cooler climate
 Anthropogenic factors
are more dominant

42. Conclusions:
 The changes in the past climate is mostly correlated
with the change of Earth-Sun geometry i. e.
Milankovitch Cycles
 The changes due to Volcanoes & solar activity is
the causes of increasing of the abruptness of the
change.
 Though with the advancement of science many
methods are developed (proxy data) to know about
the past, but the accuracy is questionable
 As the climate change is the net effect of
complex interaction of all the factors ,more
research is needed to gather the knowledge about
interactions to make our predictability more
accurate

43. What is our future?
Thank You