Question:
What physical or other environmental factors contribute to
the increase in the earth's average temperature, through the
greenhouse effect?
Replies:
Actually, the greenhouse effect does not just refer to
an "increase" in the earth's average temperature - the
earth would be a lot colder than it is right now if it
were not for greenhouse effects already operating.
The main ingredients are the composition of the atmosphere,
the kind of light we receive from the sun, and the kind
of radiation (due to the earth's current temperature and
reflecting properties) the earth returns back from the
ground and from the atmosphere into space. The greenhouse effect
involves particular molecules in the atmosphere (principally
water) that allow light from the sun to reach the surface
of the earth, but which absorb a lot of the radiation that
the earth returns, because that returned radiation is
of much longer wavelength (infrared). As you might guess,
getting the details of all this right is rather complicated,
particularly as some molecules in the atmosphere that
are not very common have a significant greenhouse effect.
It is the dramatic increase in those uncommon molecules
(carbon dioxide and methane) caused by human activities
that is supposed to be causing a temperature rise right now,
but getting the calculations right is still difficult.
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