What do scientists believe global warming is caused by?

Most scientists believe that global warming is largely caused by human beings and the way they/we run industry and transport by burning fossil fuels.

Global warming is caused by the increase in the amount of carbon dioxide and other greenhouse gases in the atmosphere.

Greenhouse gases (in this case) interact with infrared radiation. Visible and more energetic light passes through them from the Sun, heats the Earth's surface, then the greenhouse gases prevent free flow of radiant heat back to space.

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Many experts do not believe that man is a large contributor. Many do not even believe we are a small contributor. When they are asked if the possibility exists that man is contributing, any science person would have to keep an open mind and say yes, it is possible.

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During the eighteenth century, scientists began to study the effect of carbon dioxide on global temperatures. They realised that carbon dioxide is a greenhouse gas which at normal concentrations helps keep the earth at a comfortable temperature suitable for human existence. In 1896, Arrhenius completed a laborious numerical computation which suggested that cutting the amount of CO2 in the atmosphere by half could lower the temperature in Europe some 4-5°C (roughly 7-9°F) - that is, to an ice age level. Arrhenius made a calculation for doubling the CO2 in the atmosphere, and estimated it would raise the Earth's temperature some 5-6°C (averaged over all zones of latitude). His calculations did not take into account the effect of the oceans in ameliorating the effect of rising carbon dioxide levels, but in any case, no one seriously believed that global warming was coming.

Subsequent work has shown that the temperature rise up to 1940 was mainly caused by some kind of natural cyclical effect, not by the still relatively low CO2 emissions. Thus, there can be more than just one cause of global warming, and they can even overlap. Nevertheless, global warming began to accelerate, and by the 1970s, a correlation with rising carbon dioxide levels was becoming too evident to ignore.

The majority of climate scientists now believe that rising greenhouse gas levels, particularly those of carbon dioxide, are the principal cause of global warming, and that human activities are a significant factor in causing those levels to rise.