What is causing global warming?

Global warming is being caused by the build up of greenhouse gases in the atmosphere, particularly carbon dioxide, from the burning of fossil fuels (coal, oil and natural gas) and deforestation.

Global warming is a rise in average global temperature. The earth has natural heating and cooling global cycles which take place over thousands of years and cause rises and falls of sea level and encroachment and retreat of glaciers and the ice caps. These temperature variations are dominantly driven by energy from the sun with distance from the sun and the sun's current energy output being the main contributers, and the angle of the earth to the sun being next in importance. This is the energy basis for the changes in seasons and average global variations in temperature. The timing and extent of these global cycles can be roughly predicted using Milankovich Cycles, which identify our planet's position, orientation, and movement relative to the sun. A great deal of interest and concern has been raised in recent years over the impact on global temperatures by man. While these may be minor temperature perturbations relative to those caused by the sun, they may result in changes to living conditions which could greatly effect the human population. However, today's climate change is happening far too fast to be the same as other climate swings.

Some gases that contribute to Global Warming and their man-made sources:

Carbon Dioxide from power plants, from cars, trucks, and airplanes. Also deforestation is responsible for up to 25% of all carbon emissions.

Methane from rice paddies and bogs, fossil fuel productions and bovine flatulence.

Nitrous oxide from nylon and nitric acid production, fertilizers in agriculture, vehicle catalytic converters, and the burning of organic matter.

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A further answer

Greenhouse gases are gases that help trap the sun's warmth in our atmosphere. They include carbon dioxide and methane. While methane is far less abundant than carbon dioxide, its effect on global warming can be far greater. The greenhouse effect is essential to life on earth as we know it. A reduction in greenhouse gases would result in global cooling, while an increae would result in global warming and climate change.

In the absence of human activity, the amount of carbon dioxide, the most abundant greenhouse gas, remains relatively constant over a long period of time. There is, of course, a recycling of carbon to carbon dioxide and back, as plants take in carbon dioxide, convert it to organic matter, then die and decay (or are burnt in forest fires), once again giving off carbon dioxide, but this natural cycle does not alter the concentration of carbon dioxide in the atmosphere. Human activity is what causes an increase in the concentration of carbon dioxide in the atmosphere. By cutting down forests for farming, we are releasing carbon into the atmosphere. But most of all, we are doing so by burning fossil fuels.

There is a great deal of misinformation about global warming, leading many to doubt that it really exists. Until recently, an eminent scientist, although not a climatologist, had his own doubts. Richard Muller, a Physics Professor and longtime critic of climate studies, sought to address what he called "the legitimate concerns" of sceptics who believe global warming is exaggerated. The Berkeley Earth Surface Temperature project at the University of California, Berkeley, was launched with a team of physicists and statisticians, to challenge the scientific consensus on global warming but is finding that its data-crunching effort is producing results nearly identical to those underlying the prevailing view.

Professor Muller has conceded that the work of the three principal groups that have analysed the temperature trends underlying climate science is "excellent ... We see a global warming trend that is very similar to that previously reported by the other groups."
We are us humans are the one who is making the world end we made cars and that makes pollution.