Which of the following are responsible for global cooling? (A) Halocarbons (B)…
2022
Which of the following are responsible for global cooling?
(A) Halocarbons
(B) Stratospheric ozone
(C) Tropospheric ozone
(D) Sulphate aerosols
(E) Black carbon
Choose the most appropriate answer from the options given below:
Answer: B. (B) and (D) only — Concept: A climate agent changes global temperature through radiative forcing, the change it causes in Earth’s energy balance. Negative forcing promotes…
- A.
(A), (B) and (D) only
- B.
(B) and (D) only
- C.
(B), (D) and (E) only
- D.
(C) and (D) only
Show answer & explanation
Correct answer: B
Concept: A climate agent changes global temperature through radiative forcing, the change it causes in Earth’s energy balance. Negative forcing promotes cooling, while positive forcing promotes warming.
Reflective particles generally cool by sending incoming sunlight back to space; ozone and absorbing particles must be classified by the atmospheric layer and the sign of their forcing.
Application
Application: Classify each listed component by its standard global radiative effect.
Component | Forcing sign | Mechanism |
|---|---|---|
(A) Halocarbons | Positive forcing; warming influence | Halocarbons absorb outgoing infrared radiation and act as greenhouse gases. |
(B) Stratospheric ozone | Negative forcing; cooling influence | The assessed stratospheric-ozone change is ozone depletion, which gives a small negative radiative forcing. |
(C) Tropospheric ozone | Positive forcing; warming influence | Tropospheric ozone is a greenhouse gas and increases radiative forcing. |
(D) Sulphate aerosols | Negative forcing; cooling influence | Sulphate aerosols scatter sunlight and make clouds more reflective. |
(E) Black carbon | Positive forcing; warming influence | Black carbon absorbs solar radiation and darkens snow or ice after deposition. |
Contrast
The combination containing halocarbons adds a warming agent to the two cooling agents.
The combination containing stratospheric ozone and sulphate aerosols groups the two negative-forcing agents.
The combination containing black carbon adds a strongly absorbing warming agent.
The combination containing tropospheric ozone adds a greenhouse warming agent.
Cross-check and result
Cross-check: the sign test gives negative forcing only for stratospheric-ozone depletion and sulphate aerosols; halocarbons, tropospheric ozone, and black carbon have positive forcing.
Therefore, the responsible pair is stratospheric ozone and sulphate aerosols.