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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