A. sea level rise
A.
B. an increase of UVB radiation
B.
C. retreat of glaciers
C.
D. extraordinary weather patterns
D.
Correct Answer: B
সঠিক উত্তর: B
Explanation
ব্যাখ্যা
- Correct answer: (b) an increase of UVB radiation
- Why: Global warming (the long-term rise in Earth's average surface temperature due to increased greenhouse gases) does not directly cause an increase in UV-B (ultraviolet-B) radiation reaching the surface. UV-B changes are primarily driven by the state of the stratospheric ozone layer — i.e., ozone depletion (largely from ozone-depleting substances such as CFCs), not the greenhouse effect itself.
- Important distinction: Greenhouse gases trap outgoing longwave (infrared) radiation and warm the troposphere; ozone depletion changes how the stratosphere absorbs shortwave ultraviolet radiation. These are two separate physical processes, though they can interact in complex ways.
- Why the other options are possible adverse effects of global warming:
- (a) Sea level rise
- Mechanisms: (1) Thermal expansion — as ocean water warms it expands; (2) Melting of land ice — glaciers and ice sheets (Greenland, Antarctica) losing mass and adding water to the oceans.
- Consequences: Coastal erosion, higher storm surge impacts, saltwater intrusion into freshwater aquifers, displacement of low-lying populations and ecosystems.
- Evidence: Tide gauges and satellite altimetry show a clear long-term rise in global mean sea level over the 20th and 21st centuries.
