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many different factors play a role in controlling earth’s surface
temperature. scientists ( ⓐ ) these factors as either climate forcings
or climate feedbacks depending on how they operate. a forcing is
something that is imposed externally on the climate system by either
human activities or natural processes. positive climate forcings, such
as excess greenhouse gases, warm the earth, while negative forcings,
such as most aerosols produced by industrial processes and volcanic
eruptions, cool the earth. in general, the cooling caused by aerosols
is not as well understood as the warming caused by greenhouse
gases. climate feedbacks, on the other hand, either amplify or dampen
the response to a given forcing. a feedback is an energy change that
is produced within the climate system itself in response to a climate
forcing. during a feedback loop, a change in one factor, such as
temperature, leads to a change in another factor, such as water
vapor, which either reinforces or offsets the change in ( ⓑ ).1. 윗글의 문맥상 ( ⓑ )에 들어갈 가장 적합한 표현은?
① the first factor
② a new factor
③ the climate forcings
④ the cooling system