There are four major causes of climate change namely: astronomical causes, volcanic eruptions, variations in solar output and changes in earths environment as a result of human activities. The IPCC says that human activity is the main cause of the changes seen in climate. This it does through activities that emission of Greenhouse gases (mainly consist of carbon dioxide, water vapor, methane and nitrous oxide). Studies of long termed climate change have discovered a connection between the concentrations of carbon dioxide in the atmosphere and mean global temperature.
Carbon dioxide is one of the more important gases responsible for the Greenhouse effect. These Greenhouse gases are able to alter the energy balance of the earth; being able to absorb long wave back to the earths surface increase the quantity of heat energy in the earths climatic system (Ifeanyi-Obi et al 2012, Etuk et al 2012 and Jike-Wai et al, 2012). Human activity is changing the amount of Greenhouse gases in the atmosphere in three important ways:
1. Burning fossil fuels
Carbon dioxide is one of the main GHG and major contributor to the Greenhouse effect. When fossil fuels like coal, oil and gas are burned, they release GHGs. Anyadike (2009), stated that through energy creating activities like heating homes and buildings, transportation systems and cooking food, treating water to make it drinkable, heating it and piping it into homes, manufacturing from fridges, gas flaring, bush burning etc, people induce the emission of carbon dioxide into the atmosphere. Since the industrial revolution which began in 18thcentury, the amount of carbon dioxide in the atmosphere has increases by 35%. The Niger Delta region of Nigeria is reported to have over 123 gas flaring sites, making Nigeria of the higher emitter of GHGs in Africa (Akinro et al, 2008). A recent study by the world-bank (2008) revealed that Nigeria accounts for roughly 1/6 of the world wide gas flaring, Nigeria flares about 75% of her gas. The flares have apparently contributed more GHGs, hence climate change in the country.
2. Deforestation
Where forests are cut down faster they are replaced is a major contributor to climate change. This accounts for 20% of the worlds carbon emissions (more than what the entire transport sector produces). Deforestation makes such a huge contribution to carbon emissions because trees absorb carbon dioxide as they grow. If there are fewer trees left to absorb carbon dioxide, then it will build up in the atmosphere. The agriculture and the industry that replace the forest do not only damage the earths ability to absorb carbon dioxide, they often cause an additional problem by producing carbon emissions of their own. In Nigeria, the primary tropical forest cover has been decimated by 97% mostly since 1990. The remainder is supposedly protected in Cross river National park and by a two year logging ban imposed in November 2008. The main cause is the demand for wood fuel. The countrys broader forest cover was estimated at just over 12% in 2005, being depleted at a rate of 3.3% per annum (Ifeanyi-Obi et al, 2012).
3. A growing world population
As the worlds population grows, there are more people who need food, life-stock and energy. This increased demand leads to increased emissions.
4. Influence of sun
The sun is the predominant source for energy input to the earth. Both long and short term variations in solar intensity are known to affect global climate. Solar intensity variations are considered to have been influential in triggering the little ice age and some of the warming observed from 1900-1950. The sun is our main source of light and warmth. It is the driving force behind the worlds weather. We are aware that cloudy day is usually colder than a sunny one, and that night time is almost always colder than day time. It is likely then that changes in the amount of energy coming from the sun could as well affect the earths climate.
5. Greenhouse effect
The sun is the only source of external heat for the earth. Sunlight heats the earths surface during the day. As the earths surface warms up it also releases heat, but we cannot see this as light like sunlight from the sun (Udenyi et al, 2008). Sometimes, on hot days we can see the heat shimmers rising from a hot black rod. This shows us that a lot of heat is being given off by the surface. At night, when the surface is no longer heated by the sun, the earth continues to give off heat in this way. In fact at the scale of the whole earth, as much heat is given off by the earth, so it is received from the Sun. This keeps the average temperature of the earth fairly stable (Ozor et al.2009).
6. Orbital variations
Slight variations in earths orbit leads to changes in the seasonal distribution of sunlight reaching the earths surface and how it is distributed across the globe. Though there can be strong changes in the geographical and seasonal distribution (Ozor et al. 2009). The earth revolves round the sun once every year, this orbit is highly regular, but there exist tiny variations in it that affects the amount of heat received from the earth by the sun and therefore, the earths climate.
7. Ocean variability
The ocean is a fundamental part of the climatic system. Short term fluctuations (years to a few decades) represents climate variability rather than climate change. On larger time scale, alterations to ocean processes such as thermohaline circulations play a key role in redistributing heat by carrying out a very slow and extremely deep movement of water and the long term redistribution of heat in the worlds ocean. Oceans cover 70% of the surface of the earth. Water is much better than air at storing heat and the oceans of the world store an immense amount of energy much more than the atmosphere. Since the oceans are in contact with air, heat can flow between the oceans and the atmosphere.
According to Udenyi, 2010 the ocean can have a major influence on earths climate, like the wind, water in the ocean flows in a series of currents both near the surface and also deeper down. This moves heat all over the world, principally from areas nearer to the equator to areas nearer to the poles. If this did not happen, the equator will be much warmer than it is and the pole will be much colder.
8. Mountains
Mountains are the largest features found on the earths continents. The highest one in the world is over 5miles in the sky. Mountain ranges are built by the same processes that cause the continents to drift over millions or tens of millions of years. When continents collide, the rock in the middle is crunched upwards to form mountains. Most of the worlds weather occurs in the lowest 5-8miles of the earths atmosphere. Consequently, mountain ranges can disrupt the flow of air by their presence, affecting the weather and changing the climate.