INTRODUCTION Variations in the earth’s climate have has had

INTRODUCTION

 

Variations
in the earth’s climate have has had a big impact on society particularly
agriculture, fishery, water resources, and recreation activities which has been
evident in history. Such natural climate variability must be identified,
quantified, and understood if ways are to be found to minimize its negative
consequences and maximize its positive ones. In addition, human activities
could significantly alter this natural variability, and indeed may already have
done so. If we are to make informed decisions about our own future, it is
essential that we assess the climate’s sensitivity to a variety of factors,
particularly on the decade to century time scales that are of most concern to
human beings.

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NATURAL FACTORS
THAT INFLUENCE EARTH CLIMATE CHANGE

 

To
understand climate variations and climate change one should put into
consideration the natural factors that influences earth climate change.

These
factors belong to the following classes extra-terrestrial and earths Internal.
Extra-terrestrial factors are the ones that affects the earth from space,
examples are solar output, earth sun geometry and interstellar dust.

Earths
internal factors are those factors that happens within earth atmosphere and
earth crust, examples are volcanic eruptions, mountain building, atmospheric
chemistry, continental drift, greenhouse gases and atmosphere ocean heat
exchange.

 

ASTRONONICAL CAUSES
THEORIES

Understanding
climate change, seasons and impacts of natural factors of climate change began
in the 15th century through astronomy theorists proving earth orbit,
eccentricity, obliquity and precession.

 

Johannes
Kepler (1571-1630) Earth has an elliptical orbital path around the sun.

Joseph
Alphonse Adhemer (1842) Precession cycles and Alternate Hemisphere.

James
Croll (1871) Curve of eccentricity, winter temperature main for glaciation and
positive feedback mechanism.

The
Milankovitch theory (1924): Discovered and computed relationship between earth’s
orbital parameters (Precession, obliquity and eccentricity) and solar
radiation.

Summer
insolation in the polar latitudes is the main cause of glaciation

ECCENTRICITY
VARIATION

According
to Pidwirny, M. (2006, Page 53) Eccentricity
controls the shape of the earths orbit. The Earth-Sun distance, which is 149
million km, on average, varies throughout the year. The Earth passes each
semester, alternately, at perihelion, i.e. it is at this point closer to the
sun at aphelion, and i.e. it is at this point than away from the sun. The
difference between these two distances is determined by the eccentricity.

Pidwirny,
M. (2006) points out that eccentricity
varies from 0.0669 to 0.0001 currently earth is experiencing a lower
eccentricity of about 0.0167. The total orbit circle takes about 100 000 years.

The
difference in between the perihelion and aphelion is 3% and responsible for 7%
variations in solar radiation on the earth.

 

OBLIQUITY VARIATION

 

The
tilt in Earth’s axis is strongly influenced by the way mass is distributed over
the planet. Large amounts of land mass and ice sheets in the northern
hemisphere make Earth top-heavy.

Earths tilt accounts for the seasons, but many
folks don’t know that the tilt, or obliquity, of the Earth has changed over
time. During a period of 41,000 years, the tilt of the Earth’s axis changes
from 22.1° to 24.6°. This wobble, like other facets of the Milankovitch Cycles
is caused by gravitational interactions with other planets.

Currently the tilt of the Earth’s axis is 23.4°,
but 9,500 years ago when the Lauren tide Ice Sheet had just about disappeared,
the Earth’s tilt was at its maximum and the high latitudes were experiencing a
greater differential of solar radiation than usual. So, the winters were long,
dark, and cold and the summers were hot with the sun higher in the sky over
Fairbanks than now.

When the tilt is small they is less climatic
variation between the summer and winter seasons in the middle and high
latitudes.

Warmer winters allow for more snow and ice to
accumulate on the earth’s surface because less of this frozen water is melted.

The net effect of a smaller tilt would be more
extensive formation of glaciers in the polar latitude.

 

 

 

 

 

PRECESSION
VARIATION

Precession is the
change in orientation of the Earth’s rotational axis. The precession cycle takes
about 19,000 – 23,000 years.

 

The cause of
the precession is the equatorial bulge of the Earth, caused by the centrifugal
force of the Earth’s rotation (the centrifugal force is discussed in a later
section). That rotation changes the Earth from a perfect sphere to a slightly
flattened one, thicker across the equator. The attraction of the Moon and Sun
on the bulge is then the nudge which makes the Earth precession.

The
cylindrical variation of the earth’s rotation around its polar axis by this the
timing of equinoxes and solstices changes thus also called precession of
equinoxes.

Precession has
a cycle of approximately 23000 years. In the summer time like now perihelion
southern hemisphere is closer to the sun. The southern hemisphere summer
receives 4% more solar radiation than northern hemisphere. After 11000 years
northern hemisphere will be closer to the sun in the time of perihelion.

 

The Wobble of Earth’s Axis

The third orbital change that Milankovich studied is called precession, the
cyclical wobble of Earth’s axis in a circle. The motion is like a spinning top
when it is about to fall over. One complete cycle for Earth takes about 26,000
years.

By itself, the wobble of Earth’s axis does not
directly cause temperature changes like orbital shape and tilt. But it changes
the portion of the orbit at which a given season occurs – that is, it changes
when a particular season will occur.

The earth’s axis is tilted so that summer occurs in
the northern hemisphere on the left side of the Sun and winter on the right. In
13,000 years the axis has moved to where summer in the northern hemisphere
occurs on the right side of the Sun and winter on the left.

If Earth’s orbit is nearly circular, then it makes
no real difference. But if Earth’s orbit is slightly elongate, and perihelion
occurs on the right side of the, then Earth is slightly farther from the Sun on
the left side. In this case, northern summer are slightly cooler and northern
winters slightly warmer on the “Now” part of the diagram. But in
13,000 years, the axis will have shifted so that summer in the northern
hemisphere will occur on the right side of the Sun where Earth is closer, so
summers will be hotter, and winters will be colder (and longer).

This is important because glaciers need land on
which to form. Most of the land surface on Earth is now in the northern
hemisphere, so when the wobble has moved Earth’s axis so that northern winters
occur on the cooler part of the orbit, glaciers will tend to grow.

 

 

 

GLACIATION

Glaciers are massive, long-lasting, moving mass of
compacted snow and ice that forms on land moves down slope or spreads outward
under its own weight. It is formed from compacted layers of snow.

The process of glacier growth and establishment is
called glaciation

For glaciers to form they are dependent on the
amount of precipitation, the larger the glacier the snow accumulation over
time.

For glacier ice to form precipitation level should
be high at temperatures should be at its minimal snowflakes will form which
will turn into granular snow which at the optimal condition will be turned into
firm and the last state of glaciation will be the formation of glacier ice.

Glaciation is caused by the cyclical changes on the
earth’s orbit and tilt

 

DEGLACIATION

 

 

 

 

 

References

Pidwirny,
M. (2006). “Glossary of Terms: P”. Fundamentals of Physical
Geography, 2nd Edition.

http://www.physicalgeography.net/physgeoglos/p.html