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Natural and human causes of climate change
Processes or activities that cause climate change are generally refered to as climate forcing processes. The earth receives energy solely from the sun, in the form of light and ultraviolet (UV) radiation, and releases energy back to space, in the form of infrared heat.
The earth's climate is determined by the earth's stored energy which is the difference between the amount of energy received from the sun and the amount of energy the earth releases back to space.
Earth's stored energy = Energy the earth receives from the Sun - Energy the earth releases to space.
--- Global Energy Balance (GEB).
If the stored energy goes down (i.e. becomes low), the temperature (and other atmospheric variables) goes down and the earth becomes colder. When the stored energy goes up, the temperature of the earth goes up causing the earth to warm up. Any process or activity that influences the GEB either by increasing or decreasing the earth’s stored energy contributes to climate change and is qualified to be called a climate forcing process. There are are both internal forcing and external forcing processes as discussed below.
Internal and External Climate Forcing Processes
Climate forcing processes are classified as:
- Internal Climate Forcing Processes - processes operating on the GEB from within the earth.
- External Climate Forcing Processes - processes operating on GEB from outside the earth.
The major external climate forcing processes are: variations in the amount of energy received from the sun and variations in the earth’s orbit around the sun. The internal climate forcing processes include effects of oceans, continental drift, atmospheric processes, water cycle, clouds, ice and snow, land surfaces, volcanic eruptions and man-made processes (mainly industrial and agricultural)). Brief descriptions of these processes ar provided below.
The external climate forcing processes and the internal climate forcing processes except the man-made processes are grouped together as natural causes of climate change while the man-made processes are the anthropogenic or human causes of climate change. The natural causes are believed to even out eventually and are not considered to be responsible for climate change. However, the anthropogenic causes are believed to be the main causes of the change in climate from one period to the other.
Further brief discussions of the various processes mentioned above are provided below.
A. The External Climate Forcing Processes:
1. Variations in the amount of energy received from the sun
About 30-40% of the UV energy from the sun is believed to be reflected back into space after hitting earth's upper atmosphere, while the remaining 60-70% gets through to the earth. This ratio could change however, due to variations in sun’s characteristics from time to time, thus leading to changes to the the global energy balance above and hence changes in our climate
2. Variations in the earth’s orbit around the sun
Changes in the tilt of the earth’s axis, changes in the shape of earth's orbit (i.e. eccentricity) and the shifting of the equinoxes (i.e. precession) play major roles in determining variations in the amount of sun’s energy reaching the earth and hence lead to variations in the earth’s climate (i.e. Climate Change).
B. The Internal Climate Forcing Processes:
1. The Oceans
Oceans cover up to 70% of the earth. Oceans are the key source of moisture in the air through interactions with the atmosphere. Oceans also store heat efficiently, transporting it thousands of miles thus redistributing heat in time and space. The oceans and marine life also consume huge amounts of carbon dioxide. These ocean based processes exert tremendous influence on global climate and accounts for the variations.
2. Continental Drift
The surface of our earth is mostly (3/4 th) covered by water. Our current day earth is made up of 7 continents (Australia, North America, South America, Asia, Africa, Europe and Antarctica) - big landmasses separated apart by oceans. A close look at the shape of the earth, one will think that the continents look like the pieces of a jig-saw puzzle that fits into a solid mass when brought together. Actually, scientists believe that several millions of years ago, the whole earth consisted of 1 big continent surrounded by a big ocean. Over time, it is believed that the big landmass (earth) slowly broke up and take the current form it has today. Scientists proofs for this theory are: similarity between plant and animal fossils and broad belts of rocks found on the eastern coastline of South America and western coastline of Africa, which are now widely separated by the Atlantic Ocean. The discovery of fossils of tropical plants (in the form of coal deposits) in Antarctica has led to the conclusion that this frozen land at some time in the past, must have been situated closer to the equator, where the climate was tropical, with swamps and plenty of lush vegetation.
Scientists believe that the our earth is still slowly drifting and constantly changing. This constant drifting is believe to have impact on the climate because it changes the physical features of the landmass, their position and the position of water bodies. The separation of the landmasses changed the flow of ocean currents and winds, which affects the climate.
3. The atmosphere
The atmosphere stores a lot of heat or energy which comes from the sun. This energy regulates the earth's climate. Furthermore, the atmosphere composes of small particles and several gases such as oxygen, nitrogen, carbon dioxide. Some of the gases (e.g. carbon dioxide vapour, carbon dioxide, methane and nitrous oxide) are known to trap heat in the atmosphere thus increasing the net “energy” stored and contributing to earth warming. The later forms of gases are referred to as “greenhouse gases (GHG)”. The earth climate is also affected by the particles in the atmosphere which tend to block sunlight reaching the earth.
4. Water Cycle
Higher air temperatures can increase water evaporation and melting of ice. And while water vapour is the most potent greenhouse gas, clouds also affect evaporation, creating a cooling effect.
5. The Clouds
Clouds reflect solar energy (cooling the earth) and thereby trapping heat being radiated up from the surface (warming the earth). Clouds variability contribute to climate change
6. Ice and Snow
The whiteness of ice and snow reflects heat out, cooling the planet. When ice melts into the sea, this drives heat from the ocean causing variability in climate.
7. Land Surfaces
Mountain ranges can block clouds, creating "dry" shadows downwind. Sloping land allows more water runoff, leaving the land and air drier. A tropical forest will soak up carbon dioxide, but once cleared for cattle ranching, the same land becomes a source of methane, a greenhouse gas.
8. Volcanic Eruptions
A volcanic eruption, lasting for few days, emits large volumes of sulphur dioxide (SO2), water vapour, dust, and ash into the atmosphere that influence climatic patterns for years. The gases and dust particles partially block the incoming rays of the sun, leading to cooling (more details on: http://edugreen.teri.res.in/explore/climate/causes.htm)
9. Man Made Climate Change(Human Causes)
All the processes discussed above are natural causes. The natural causes even out eventually due to earth balance. In other words, the net energy change from the natural causes iz zero. Climate change is therefore considered to be primarily caused by human or anthropogenic activities. Human industrial and agricultural activities are believed to be adding to the amount of "greenhouse gases" naturally present in the atmosphere. These gases trap heat that are otherwise supposed to be lost to the space from the earth and consequently warm up the earth. Human activities in the Industry and the agricultural sectors are believed to be responsible for the increasing quantities of carbon dioxide, methane and other greenhouse gases in the atmosphere. For more details go to - Greenhouse Gases. For more information on human activities influencing climate change and the environment, please follow the link: Human Contributions to Climate Change
Other Sources of Information:
- Intergovernmental Panel on Climate Change (IPCC)
- United Nations Framework Convention on Climate Change
- World Meteorological Organization (WMO)
- United Nations Environmental Programme (UNEP).
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