Difficulty: Easy
Correct Answer: Both (A) and (R) are true, and (R) is the correct explanation of (A).
Explanation:
Introduction / Context:This item links observed global warming to the greenhouse effect, a foundational climate concept.
Given Data / Assumptions:
Concept / Approach:The enhanced greenhouse effect, due to increased greenhouse gas concentrations, explains observed warming.
Step-by-Step Solution:
1) (A) True: long-term upward trend in global average temperature is well-documented.2) (R) True: greenhouse effect is a real physical mechanism.3) (R) causally explains (A): enhanced greenhouse forcing raises equilibrium temperatures.Verification / Alternative check:Short-term variability (e.g., ENSO) does not negate the long-term trend or the forcing mechanism.
Why Other Options Are Wrong:They deny either the observation, the mechanism, or their causal connection.
Common Pitfalls:Confusing weather variability with climate trends; ignoring radiative forcing basics.
Final Answer:Option A: Both true; (R) correctly explains (A).
Discussion & Comments