Previous Year Question
The scientific view is that the increase in global temperature should not exceed 2°C above pre-industrial level. If the global temperature increases beyond 3°C above the pre-industrial level, what can be its possible impact/impacts on the world?
Terrestrial biosphere tends toward a net carbon source.
Widespread coral mortality will occur.
All the global wetlands will permanently disappear.
Cultivation of cereals will not be possible anywhere in the world.
Select the correct answer using the code given below:
1 only
1 and 2 only
2, 3 and 4 only
All of these
Correct Answer: B
Detailed Solution
An increase of more than 3°C in global temperature may produce extensive and severe effects on ecosystems, oceans, agriculture and human societies.
Statement 1 is correct: Terrestrial ecosystems currently absorb a large quantity of carbon dioxide from the atmosphere through photosynthesis.
Forests, soils and peatlands are important terrestrial carbon stores and carbon sinks.
As temperature increases, the rates of plant and soil respiration may rise, returning stored carbon to the atmosphere more rapidly.
Extreme heat, drought, wildfires, insect outbreaks and forest mortality may reduce the carbon-absorption capacity of terrestrial ecosystems.
Thawing of permafrost may cause the decomposition of frozen soil organic matter and release carbon dioxide and methane.
If carbon release becomes greater than carbon absorption, the terrestrial biosphere may change from a net carbon sink to a net carbon source.
This change may generate additional warming and further intensify climate change.
Statement 2 is correct: When seawater temperature rises, corals expel their symbiotic zooxanthellae because of thermal stress.
This process is called coral bleaching. If the stress continues for a long period, widespread coral mortality may occur.
Increasing frequency and intensity of marine heatwaves may not provide corals sufficient time to recover between bleaching events.
Ocean acidification also makes the formation of calcium-carbonate skeletons difficult for corals and reduces the recovery capacity of reefs.
Statement 3 is incorrect: Rising temperatures may seriously affect many wetlands, but the permanent disappearance of all the world’s wetlands is an extreme and absolute claim.
Some wetlands may shrink, migrate or change ecologically, while new wetlands may also develop in certain regions.
Statement 4 is incorrect: Higher temperatures, drought and irregular rainfall may reduce cereal yields and nutritional quality, but cereal cultivation will not become completely impossible at every location in the world.
Changes in sowing dates, water management, heat- and drought-tolerant varieties and geographical shifts in cultivation zones may help continue cereal production in certain regions.