Radiative forcings are changes imposed on the planetary energy balance; radiative feedbacks are changes induced by climate change. Forcings can arise from either natural or anthropogenic causes. For example, the concentration of sulfate aerosols in the atmosphere can be altered by volcanic action or by the burning of fossil fuels. The distinction between forcings and feedbacks is sometimes arbitrary; however, forcings are quantities normally specified in global climate model simulations, while feedbacks are calculated quantities. Examples of radiative forcings are greenhouse gases (such as carbon dioxide and ozone), aerosols in the troposphere, and surface reflectivity. Radiative feedbacks include clouds, water vapor in the troposphere, and sea-ice cover.

The effects of forcings and feedbacks on climate are complex and uncertain. For example, clouds trap outgoing radiation and thus provide a warming influence. However, they also reflect incoming solar radiation and thus provide a cooling influence. Current measurements indicate that the net effect of clouds is to cool the earth. However, scientists are unsure if the balance will shift in the future as the atmosphere and cloud formation are altered by the accumulation of greenhouse gases. Similarly, the vertical distribution of ozone affects both the amount of radiation reaching the earth’s surface and the amount of reradiated radiation that is trapped by the greenhouse effect. These two mechanisms affect the earth’s temperature in opposite directions.

1. It can be inferred from the information in the passage that “burning of fossil fuels” (Highlighted)

(A) is an anthropogenic cause of radiative forcings.
(B) results in both radiative forcings and radiative feedbacks.
(C) does not affect atmospheric forcings or feedbacks.
(D) is a significant type of radiative forcing.
(E) is an anthropogenic cause of radiative feedbacks.


2. According to the passage, radiative forcings and radiative feedbacks can generally be distinguished in which of the following ways?

(A) Whether the radiative change is global or more localized
(B) The precision with which the amounts of radiative change can be determined
(C) The altitude at which the radiative change occurs
(D) Whether the radiative change is directed toward or away from the earth
(E) Whether the amount of radiative change is specified or calculated


3. The author discusses the effect of clouds on atmospheric temperature most likely in order to show that

(A) radiative feedbacks can be more difficult to isolate and predict than radiative forcings.
(B) the climatic impact of some radiative feedbacks is uncertain.
(C) some radiative feedbacks cannot be determined solely by global climate model simulations.
(D) the distinction between radiative feedbacks and radiative forcings is somewhat arbitrary.
(E) the effects of radiative forcings on planetary energy balance are both complex and uncertain.