Life on Earth is possible because of the fine energy balance between the energy Earth receives and the energy that goes back into the atmosphere.
The energy balance maintains average weather conditions for a very long period of time on earth.
The sole source of all the energy present in the Earth is the Sun. The earth receives energy in the form of sunlight. The surface of the earth absorbs more than 50% of the sunlight. The rest 50% sunlight gets reflected by the earth surface in the form of heat.
The reflected heat energy while on its way back reaches the lower atmosphere. Greenhouse gases are present in the lower atmosphere. They absorb heat energy and reflect it back in all the directions. A part of heat energy comes back in the direction of the earth.
This heat trapping is known as greenhouse effect.
In absence of the Greenhouse Effect the average global temperature would have been -18 0C. Because of the Greenhouse effect the average global temperature rises from -18 0C -to ~14 0C. Life becomes possible because of it for the inhabitation of the present form of life.
The earth’s climatic system changes when the balance between the incoming energy on earth and the energy going away from earth gets changed.
Any factor that disturbs this balance may cause climate change. Climate change is known as the long term changes in the average weather conditions on earth.
Indicators of Climate Change
The indicators of climate changes are shifts in the temperature, precipitation, winds, and other natural processes for a very long period of time.
Any change in the factors responsible for maintaining the Energy balance on Earth can contribute towards climate change. Long term average weather conditions on earth are dependent on these factors.
Depending upon the change in the factors the climate can get shifted to a new long term state. The new state could be cooler or warmer than the previous long term state. These factors are termed as climate forcers reflecting the fact that they are not the part of the climate system but force the climate system to change from outside.
What are the Causes of Climate Change ?
1. Natural Factors that can Cause Climate Change
There are many natural events that can change the earth’s energy balance and can be the cause of climate change.
Volcanic activities and solar radiations are the natural factors that can bring climatic changes.
Climate Change due to Volcanic Eruptions
Out of these two the volcanic eruptions have short term effect on the climate. When volcanoes erupt, a mixture of gases and particles are released into the air.
Based on the nature of the gases and mixtures volcanic erruptions may have cooling or warming impacts on climate. For example: Ash and Sulphur dioxide reflect sunlight away from the earth. Their emission can have a cooling effect while the emission of CO2 cause warming.
Climate Change due to Solar Activities
Since the late seventeenth century the number of sun spots on the surface of the Sun has risen. The more sun spots are equivalent to more solar activity.
Sun spots are cooler places on the surface of earth but, they’re accompanied by hotter, brighter patches known as faculae.
The overall brightness of the sun rises by 0.1% at visible wavelengths, and more at ultraviolet wavelengths. Many scientists held these responsible for about half of the global warming (~0.6 ºC) observed over the last 110 years (IPCC, 2001).
According to the observations by the Earth Observatory, NASA If the Sun’s spots and faculae begin to disappear over the next century, the Sun could partially counter global warming. On the other hand, if the number of sun spots rises, the planet will face further warming.
You can also check out : What is Global Warming
2. Human Induced (Anthropogenic) Causes of Climate Change
In the last 150 years, the extent of Greenhouse Gas emissions because of human activities have increased exponentially. These emissions influence the energy balance of the earth.
Based on the nature of these emissions they can exert cooling or warming effect. For example; sulphur dioxide causes cooling effect while carbon dioxide (CO2) gas exerts warming effect.
CO2 and some other greenhouse gases exerting the warming effect actually add to the natural greenhouse effect of the atmosphere.
Since the amount of CO2 emissions far exceeds than the emissions that cause cooling, the earth is observing overall warming.
The fifth assessment report of the IPCC reaffirms the finding that more than half of the increase in the observed global average surface temperature is because of the increase in the greenhouse gas emissions due to anthropogenic activities.
By the combustion of the fossil fuels and during the manufacturing processes in the factories CO2 is emitted. This is the most emitted gas. Its shelf life in the atmosphere is also very long. Its life time in the atmosphere is upto 200 years as against the shelf life of methane (12 years).
The very high concentration and long life in the atmosphere makes CO2 a strong long term climate change forcer.
The other greenhouse gases that get emitted due to human activities are methane, nitrous oxide, chlorofluorocarbons etc.
As said above, the natural greenhouse effect of the atmosphere is responsible for the life in our planet. It is the additional greenhouse effect caused by the emissions due to human activities that is a matter of concern.
This continuous addition in the greenhouse gas concentration in the atmosphere may take the earth up to the warming level never experienced before. This will have environmental, social and economic repercussions.
According to the IPCC 5th assessment report it is extremely likely that the combined effect of very high atmospheric concentration of CO2, methane, nitrous oxide and chlorofluorocarbon have been the dominant cause of observed warming since mid 20th century.
About 40% (880 Gt) of the total emitted CO2 is still present in the atmosphere. The rest of the gas had been absorbed. Land, plants, soils and oceans absorb large chunk of CO2 from the atmosphere. The absorption of CO2 by ocean leads to the ocean acidification.
The IPCC report also says that about half of the total emissions have happened in the last 40 years.
IPCC: United Nations has set up a panel called ‘Intergovernmental Panel on Climate Change (IPCC). The panel comprises of hundreds of climate scientists from around the world. The scientists working for IPCC gather the global data and state of the art research on global temperatures, climate change and its impact. Based on the assessments of these data and research, IPCC publishes its Assessment Reports.
Anthropogenic: Caused or Influenced by humans