Climate change

Definition

The UNFCCC (United Nations Framework Convention on Climate change) defined climate change as a ‘change of climate related with directly or indirectly with human activity that changes the atmospheric components and in addition related with natural climate variability observed over comparable time periods’. These changes result from external and internal impacts and human activities. 

Causes of climate change

Earth climate mainly determine by two factors. (i) Terrestrial factors (from ocean, atmosphere and land systems) (ii) Extraterrestrial factors (from extraterrestrial systems). Base on this primarily divide the factors into three that cause changes in earth climate.

1. Variations in the Earth’s orbital characteristics
2. Atmospheric carbon dioxide variations
3. Solar variability 

1. Variations in the Earth’s orbital characteristics

According to milankovitch theory, amount of solar radiation that received by earth’s surface vary in three cycle events. The first cycle is happen by eccentricity. It’s determined the shape of earth’s orbit around the sun. The orbit changes from elliptical to circular and then back to elliptical in a period of 100,000 years. These changes make greater variation in solar energy that received by top of the atmosphere. This occurs due to Earth’s closet (Perihelion) and farthest orbit from the sun. 

The second cycle is results from the Earth’s rotate on its polar axis. It changes the orbital timing of the equinoxes and solstices. It has a cycle of approximately 26,000 years. The third cycle related with the tilt of Earth’s axis of rotation. During the 41,000 year cycle the tilt can deviate from approximately 22.5 to 24.5. When the tilt is smaller there is a less climatic variation occur in middle and high latitudes. 

2. Atmospheric carbon dioxide variations 

Long term researchers on climate change show the connection between the concentration of carbon dioxide and global temperature. Carbon dioxide consider as an important gas in greenhouse effect. Certain atmospheric gases, like carbon dioxide, water vapor and methane are able to alter the energy balance of the Earth. They absorb long wave radiation. The result of this processes re-emission of long wave back to the Earth’s surface. It increases the quantity of heat energy in earth’s climatic system. 

Oceans were greater store of carbon dioxide and control the movement of this gas from atmosphere. The amount of carbon dioxide that can be held in the ocean determine by the function of temperature. It released from ocean when the global temperature increases. If temperature reduces it will diffuse into the ocean. 

Over the three decades, carbon dioxide concentration has been increasing in atmosphere because of human activities. Burning of fossils fuels, changes in farmland and deforestation have released carbon dioxide into the atmosphere. In 1700 it concentration was 280 parts per million and it increase to 380 parts per million in 2005. This higher concentration of carbon dioxide in the atmosphere will alter the global warming. Computer models predict that globe will warm up by 1.5-4.5 Celsius if the carbon dioxide reaches the predicted level of 600 parts per million by the year 2050. 

Many climatologists observed the connection between the volcanic eruptions and short term climatic change. Best example was eruption of Tambora volcanic in 1815. This eruption led to global cooling. Volcanoes emit huge amount of greenhouse gases including Co². 

3. Solar Variability

Climatologists link sunspots with climatic change. Sunspots are referred as magnetic storms that are seen as dark areas on the sun’s surface. The number and size of sunspots show cyclical patterns. It contains 11, 90 and 180 years cycle. 

These sunspots are responsible for the solar variations. Observed in early 1980’s solar energy decreased by 11 year sunspot activity. During the middle of the little ice age (1650-1750) indicated very little sunspot activity on the sun’s surface. 

During the periods of maximum sunspot activity, the sun magnetic field is strong. When sunspot activity is low, the magnetic fields weaken. 

References : 

(1) Kevin T. Pickering an Lewis A.Owen (1997); An introduction to global environmental issues; London and New york

(2) http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm

(3) http://science.nasa.gov/science-news/science-at-nasa/2009/01apr_deepsolarminimum/