Scientists have spent decades figuring out what is causing global warming. They’ve look at the natural cycles and events that are known to influence climate. But the amount and pattern of warming that’s been measured can’t be explained by these factors alone. The only way to explain the pattern is to include the effect of greenhouse gases (GHGs) emitted by humans.

The causes of global warming practically are by many things around us. It is mainly caused by emissions of carbon dioxide and other heat-trapping gases that are emitted primarily by the burning of fossil fuels and the clearing of forests. These gases remain in our atmosphere for decades or even centuries.

Sometimes, even we, ourselves are doing harm to the environment at times without realizing it. Using plastics bags is one example. Plastic bags are non-degradable, thus it cannot be disintegrate easily. Therefore, we have to think thrice before taking an action.

Causes of global warming
Ø Natural causes

· Obviously created by nature
· Release of methane, a combustible, greenhouse gas, that traps heat in the Earth’s atmosphere, from arctic tundra and wetland.
· The Earth goes through a cycle of climate change, usually lasting about 40,000 years.
· It can take the Earth thousands of years to warm up or cool down just 1 degree when it happens naturally.
· In addition to recurring ice-age cycles, the Earth's climate can change due to volcanic activity, differences in plant life, changes in the amount of radiation from the sun, and natural changes in the chemistry of the atmosphere.

Several greenhouse gases are responsible for global warming, and humans emit them in a variety of ways.

Ø Man-made or anthropogenic causes

· Contributes the greatest damage to global warming.
· Most come from the combustion of fossil fuels in cars, factories and electricity production.
· The gas responsible for the most warming is carbon dioxide (CO2), a colourless gas that is a by-product of the combustion of organic matter.
· Other contributors include methane released from landfills and agriculture (especially from the digestive systems of grazing animals), nitrous oxide from fertilizers, gases used for refrigeration and industrial processes, and the loss of forests that would otherwise store carbon dioxide.

ü Pollution

· Pollution is one of the biggest man-made problems, available in any form, such as burning fossil fuels.
· Fossil fuels are fuels made of organic matter like coal, or oil.
· By mining coal and oil, methane will occur naturally through the decomposition of organic material and is often encountered in the form of "swamp gas."

ü World population

· Another major man-made cause of global warming is an increase in world population.
· It leads to increase in consumption of goods and services.
· Wastes produced will cause air pollution, as during the process of incinerating wastes, dust particles will be released into the air.
· Furthermore, there may be also land pollution due to the improper disposal of waste, such that great heaps of rubbish is either left in public places or at illegal dumping grounds.

As the world population increases, the number of vehicles especially in urban area also increases. In many cities, it is estimated that as much as 90% of dust and smoke particles present in the air are emitted by vehicles. These emissions contain harmful gases, such as carbon monoxide and nitrogen oxides.

How greenhouse gases contribute to greenhouse effect, leading to global warming?

· Methane acts much like carbon dioxide in the atmosphere, absorbing infrared energy and keeping heat energy on Earth.
· While there isn't as much methane as carbon dioxide in the atmosphere, methane can absorb and emit twenty times more heat than CO2.
· These greenhouse gases in the atmosphere traps heat from the Sun’s rays, keeping the Earth warm for living things to survive.
· However, these gases do not break down easily.
· Hence, they accumulate in the atmosphere.
· This causes more heat from the Sun to be trapped in the lower atmosphere, resulting in an increase in air temperatures throughout the world, known as global warming.

The profound impact rising temperatures have had in the Arctic provides a window into a future we may all experience. With continued warming, we can expect more extreme heat and drought, rising sea levels, and higher-intensity tropical storms. At risk are our coastal property and resources, the liveability of our cities in summer, and the productivity of our farms, forests, and fisheries.

We can’t avoid all the consequences of global warming, but committing ourselves to action today can help ensure our children and grandchildren inherit a healthy world full of opportunity.

Acknowledgements:
http://www.ucsusa.org/global_warming/science/
http://science.howstuffworks.com/global-warming3.htm
http://science.nationalgeographic.com/science/environment/global-warming/gw-causes.html
http://library.thinkquest.org/J003411/causes.htm
Source: Secondary 2 Geography Earth Our Home textbook

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