natural causes of climate change
TRANSCRIPT
Natural causes of climate change
Debasish Chakraborty Roll No - 4843
Division of Agricultural Physics
Climate VariabilityInherent characteristics of earth’s climate which manifests itself in changes of climate with time
Climate ChangeIt 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
Solar OutputEarth-Sun Geometry
Interstellar Dust
Earth’s Internal
Volcanic EruptionMountain Building
Continental Drift
Atmosphere-Ocean Heat Exchange
Atmospheric Chemistry
Natural Factors Influencing Earth’s Climate
Extraterrestrial
Earth-Sun GeometryMotion 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 YearsShifting of Solstices & Equinoxes
Wandering of Poles
Chandler’s Motion
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 CrollCurve 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
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
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’.
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
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
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
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 DataThe Oxygen isotopic composition (δ 18O)
Estimate of summer sea surface temperature at the core site(Ts)Percentage of Cycladophora davisiana
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
Fig; Variations in obliquity, precession, and the corresponding frequency components of climate over the past 500,000 years
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’
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
Evolution of present continental conformation
Altering the Distribution of Land Masses
Changing Continental Elevation
Variability in Atmospheric Concentration of CO2
Major Factors of Major Effects of Plate Tectonics
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:
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
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
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
Volcanoes
VEI 0 1 2 3 4 5 6 7 8
Eject Volume
<10,000 m3
>10,000 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
Stromboli
Galeras (1993)
Cordon Caulle (1921
Eyjafjallajokull (2010)
Mt. St. Helnes (1980)
Mt. Pinatubo 1991
Tambora (1815)
Taupo (26,500 BP)
Frequency many Many 3477 868 421 166 51 5 0
Volcanic Eruption:
Influence of Volcanoes
Very Short Term
Volcanic ash
Short Term Mid to Long TermAerosol
Atmospheric Circulation
Hydrological Cycle
Ocean
Scientists belief that volcanoes are having profound effect on climate. But these effects are time dependent.
These ashes lasts for few months
Blocks the penetration of sunlight into the atmosphere
Tropospheric temperature drops down
Volcanic ash
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
Hydrological CyclePrecipitation 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
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
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
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%
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
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
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
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%.
Cosmic Ray & The Earth’s Temperature
Swensmark showed that the increase of air temperature by 0.30c 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)
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.
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
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
IPCC WG1 AR4
Observed Changes and Future Prediction Natural factors leading to a cooler climate
Anthropogenic factors are more dominant
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
What is our future?
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