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What causes global warming?
Today’s global warming is caused mainly by human activities that increase heat-trapping greenhouse gases, especially fossil fuel burning. The greenhouse effect is natural; the problem is its human-driven strengthening.
Global warming is caused mainly by human activities that increase greenhouse gases in the atmosphere, especially the burning of coal, oil and gas. The gases slow the escape of heat from Earth’s system. The greenhouse effect itself is natural and necessary for life; the warming trend is intensified when human emissions add more heat-trapping gases than natural processes alone would produce.
How the greenhouse effect works
Sunlight reaches Earth, where the surface absorbs energy and releases some of it as infrared heat. Greenhouse gases absorb and re-radiate part of that outgoing heat, slowing the rate at which it escapes to space. NASA describes this effect as a normal feature of Earth’s atmosphere that supports life. Human activity has strengthened the effect by raising concentrations of heat-trapping gases. [1]
This mechanism is sometimes misunderstood as a physical lid that traps all heat. A better picture is a change in how readily energy leaves the atmosphere: more greenhouse gases make heat loss slower, shifting the balance until the climate system warms. That basic process helps explain why emissions matter even though greenhouse gases make up only part of the atmosphere.
Carbon dioxide from fuels and land use
Carbon dioxide is released by natural processes and human activities. NASA identifies burning fossil fuels and deforestation among human sources. [1] When coal or oil burns, carbon combines with oxygen in the air to form carbon dioxide. Clearing land can also add greenhouse gases and reduce the amount of vegetation available to absorb carbon as it grows.
The scale and persistence of emissions matter. Carbon dioxide accumulates in the atmosphere, so continued additions raise its concentration. A household’s energy use is one part of a larger system shaped by electricity generation, transport, buildings and industry. The cause of global warming is not reducible to individual choices alone; understanding the mechanism helps explain why changing energy systems and reducing emissions across sectors matter.
Other gases contribute too
Methane and nitrous oxide also trap heat. NASA describes methane sources that include wetlands, landfills, rice farming, livestock digestion and manure, as well as leaks from fossil fuel production and transport. It identifies fertilizer production and use, fossil fuel burning and vegetation burning as sources of nitrous oxide. [1] Different gases have different sources and atmospheric behavior, so a complete account of warming looks beyond carbon dioxide.
Water vapor is also a greenhouse gas, but NASA explains that it is mainly a feedback: as oceans warm, more water vapor enters the atmosphere and can amplify warming. It is not the direct cause of the current climate change trend. [1] This distinction between a driver and a feedback helps avoid the mistaken conclusion that the most abundant greenhouse gas must be the original cause of the warming now observed.
Why the Sun is not the explanation for today’s trend
The Sun’s energy varies, and solar changes have influenced climate in the past. But NASA reports that solar energy received by Earth has followed a small natural cycle without a net increase since 1880, while global temperature has risen. It also notes that the current warming cannot be reproduced by climate models without rising greenhouse gases. [1] These comparisons help distinguish a possible natural influence from the cause that best explains the observed modern trend.
This is a useful example of how climate science tests explanations: a proposed cause should match the timing and pattern of observations. NASA also notes that warming at the surface and lower atmosphere alongside cooling in the upper atmosphere is consistent with greenhouse gases slowing heat loss, rather than a more active Sun warming all atmospheric layers. [1]
From cause to practical response
The causes point toward the kinds of changes that can reduce warming: lowering emissions from energy, land use, transport and other activities that release greenhouse gases. The United Nations describes net zero as cutting emissions to a small residual amount that can be durably absorbed or stored, while emphasizing that commitments need credible action. [2] That definition concerns the balance of emissions and removals; it does not mean that every emission disappears immediately or that a pledge alone changes the atmosphere.
For a practical starting point, identify the energy or travel decisions within your control and also consider what collective decisions shape them, such as building efficiency or cleaner electricity. An individual action can be worthwhile, but the physical cause is the accumulation of greenhouse gases from human activities at broad scale. The next useful question is which source of emissions your household or community can realistically reduce, and what larger changes would make that reduction easier.
Follow the evidence
Primary sources used in this story. Practical examples are illustrative unless a source states otherwise.
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