Answer :
The so-called greenhouse gases. The one most of us know is carbon dioxide, although I guess there are even more dangerous matters in there.
Earth’s temperature depends on the balance between energy entering and leaving
the planet’s system . When incoming energy from the sun is absorbed by
the Earth system, Earth warms. When the sun’s energy is reflected back
into space, Earth avoids warming. When energy is released back into
space, Earth cools. Many factors, both natural and human, can cause
changes in Earth’s energy balance, including:
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Models that account only for the effects of natural
processes are not able to explain the warming over the past century.
Models that also account for the greenhouse gases emitted by humans are
able to explain this warming.
Source: USGRCP (2009) Changes in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphereVariations in the sun’s energy reaching EarthChanges in the reflectivity of Earth’s atmosphere and surface
Source: USGRCP (2009) Changes in the greenhouse effect, which affects the amount of heat retained by Earth’s atmosphereVariations in the sun’s energy reaching EarthChanges in the reflectivity of Earth’s atmosphere and surface