What is the reason for global warming?

Answer 1

1. Deforestation
2. Burning of fossil fuel, coal, oil and natural gas.

To answer, it is important to understand the global climate is a balance that has been achieved through natural processes that can be boiled down to two effects: greenhouse gas production or emission, and greenhouse gas consumption. Greenhouse gases are gases in our atmosphere that retain heat from sources such as the sun instead of letting excess heat emit out into space. The more greenhouse gases (such as carbon dioxide) are present in the atmosphere, the more heat will build up in the earth's atmosphere. There are several factors on both sides, but -- prior to the widescale use of fossil fuels by humans such as oil or coal, the primary sources of greenhouse gas emissions were breathing by animals, wildfires and volcanoes and the primary consumption (or reduction) in greenhouse gases is from the process plants use called photosynthesis, in which they take in carbon dioxide and sunlight, use the carbon out of the carbon dioxide, and release free oxygen. By using the carbon (to make sugars, using energy they have from sunlight to separate the carbon from carbon dioxide), they take it out of the atmosphere.

Over eons, nature achieves something of a balance between production and consumption of carbon dioxide; the level does not hold precisely steady, but had achieved a gradual reduction in carbon dioxide over time and an increase in pure oxygen. For a certain amount of carbon dioxide in the atmosphere, a certain amount of the sun's heat will stay in the earth's atmosphere (heating up our atmosphere) instead of being let out into space (letting our atmosphere cool down).

Anthropogenic (man-caused) global warming is occurring because we have greatly increased the emission of carbon dioxide, putting more in than photosynthesis can take out, and we have also clear-cut large swaths of forest, meaning nature can no longer remove as much carbon out of the atmosphere as it could. This has radically flipped the carbon dioxide trend from gradual reduction of carbon dioxide to relatively rapid increase in carbon dioxide. Since carbon dioxide is a greenhouse gas, this means that the atmosphere will retain more heat and the global climate will have an overall increase in temperature, what we call global warming.
pollution