Correct Option
Statement 1: A global temperature increase beyond 3°C above pre-industrial levels is projected to cause the terrestrial biosphere to transition from a net carbon sink to a net carbon source. This shift occurs due to several factors, including increased frequency and intensity of forest fires, enhanced decomposition of organic matter in soils leading to higher soil respiration, and the thawing of permafrost, which releases vast amounts of stored carbon and methane into the atmosphere.
Statement 2: Coral reefs are highly sensitive to ocean temperature increases. A rise of 3°C would lead to widespread and severe coral bleaching events. Bleaching occurs when corals expel their symbiotic algae (zooxanthellae) due to thermal stress, leading to the loss of their primary food source and color. Prolonged or severe bleaching results in extensive coral mortality, significantly impacting marine biodiversity and ecosystem services.
Incorrect Options
Statement 3: The assertion that all global wetlands will permanently disappear is an overstatement. While many wetlands, particularly coastal and estuarine wetlands, are highly vulnerable to sea-level rise, increased salinization, and altered hydrological regimes, not all wetlands globally are projected to disappear. Inland wetlands, though subject to changes in precipitation patterns and water availability, may persist, albeit with altered ecological characteristics. The complete disappearance of all global wetlands is not a universally accepted scientific projection even under a 3°C warming scenario.
Statement 4: The claim that cultivation of cereals will not be possible anywhere in the world is an extreme and inaccurate projection. While a 3°C increase in global temperature would severely impact agricultural productivity through increased frequency of extreme weather events (such as droughts, floods, and heatwaves), shifts in climatic zones, and changes in pest and disease patterns, it would not eliminate cereal cultivation globally. Some regions might experience reduced yields or become unsuitable for current crops, while others, particularly in higher latitudes, might initially see some benefits from longer growing seasons or new arable land, before facing other challenges. Adaptation strategies and technological advancements would also play a role in mitigating some impacts.
Based on the above, only statements 1 and 2 are accurate potential impacts. Therefore, options (A), (C), and (D) are incorrect as they either exclude correct statements or include incorrect ones.