- Some proposals for climate change mitigation involve 'carbon capture and storage' (CCS), where CO₂ from industrial sources is captured and injected into deep geological formations. What is a primary environmental concern associated with this technology?
Answer: The captured CO₂ could potentially leak back into the atmosphere over long timescales or through seismic activity.
The correct answer is B. A major challenge and concern for geological sequestration is ensuring the long-term permanence of the storage. There is a risk that geological instability, fractures, or improperly sealed injection sites could allow the stored CO₂ to leak back into the atmosphere, negating the climate benefit. A is a potential issue, but the primary environmental concern is the integrity of the storage. C is incorrect; the process is designed to store CO₂, not release other gases. D is incorrect; CO₂ is not flammable and will not combust.
- Biomagnification of pollutants like mercury can be exacerbated by climate change. What is a plausible mechanism for this interaction?
Answer: Changes in food web structure, such as the loss of certain prey species due to warming, can force predators to consume prey from higher trophic levels with greater pollutant loads.
The correct answer is C. Climate change can alter species distribution and abundance, thus changing the structure of food webs. If a predator's usual prey becomes scarce, it might switch to consuming other predators, effectively feeding at a higher trophic level. Since persistent pollutants biomagnify up the food chain, this change in diet would lead to the predator accumulating a higher concentration of the pollutant. A is possible but less of a direct link to biomagnification itself. B describes the opposite of what is generally expected. D describes a nonexistent chemical interaction.
- Rewilding is an approach to conservation that aims to restore ecosystem processes. How can the reintroduction of a keystone species, such as the wolf, contribute to mitigating climate change effects at a local level?
Answer: By controlling herbivore populations, wolves can prevent overgrazing, allowing forests to regenerate and sequester more carbon.
The correct answer is B. This describes a trophic cascade. By preying on large herbivores like deer or elk, wolves can reduce grazing pressure on young trees. This allows forests to grow and regenerate more effectively. Healthy, growing forests are significant carbon sinks, sequestering atmospheric CO₂ in their biomass. A is biologically impossible. C is incorrect; wolves do not significantly change the landscape's albedo. D is incorrect; while animals produce some methane, it is negligible compared to the positive effect on carbon sequestration from forest regeneration.
- Long-term data show a strong positive correlation between atmospheric CO₂ concentrations and average global temperatures. From a scientific perspective, what is the most appropriate conclusion to draw from this correlation alone?
Answer: The correlation suggests a strong association, which is supported by a known physical mechanism (the greenhouse effect), making a causal link highly probable.
The correct answer is C. This reflects proper scientific reasoning (Nature of Science). Correlation does not, by itself, prove causation. However, when a strong correlation is coupled with a well-understood physical mechanism (the greenhouse effect), the evidence for a causal relationship becomes very strong. A is too strong a statement; correlation alone does not prove causation, and other factors can influence climate. B is incorrect because dismissing the correlation is unwarranted given the known physics. D describes a feedback mechanism that does exist (warmer oceans hold less CO₂), but it is not the primary driver of the current rapid increase in CO₂; anthropogenic emissions are.
- The increase in atmospheric CO₂ concentration leads to ocean acidification. Which chemical change is the primary reason this is detrimental to marine calcifying organisms like corals and molluscs?
Answer: Increased hydrogen ion concentration (lower pH) leads to a reduction in the concentration of available carbonate ions (CO₃²⁻).
The correct answer is B. When CO₂ dissolves in seawater, it forms carbonic acid (H₂CO₃), which dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻). The excess H⁺ ions react with available carbonate ions (CO₃²⁻) to form more bicarbonate. This reduces the concentration of carbonate ions, which calcifying organisms need to build their calcium carbonate (CaCO₃) shells and skeletons. A is an oversimplification; while corrosion can occur in very acidic conditions, the main problem is the inhibition of new skeleton formation. C describes deoxygenation, a separate issue related to warming, not the chemical mechanism of acidification. D is incorrect; bicarbonate ions are not toxic and are a key part of the buffering system.
- The Earth's climate has changed naturally in the past. What key feature distinguishes current, anthropogenic climate change from most past natural climate fluctuations, such as ice age cycles?
Answer: The rate of increase in both greenhouse gas concentrations and global temperature is exceptionally rapid.
The correct answer is C. While the Earth's climate has always changed, the defining characteristic of the current event is the unprecedented speed. The rate at which CO₂ is being added to the atmosphere and the resulting rate of temperature increase are much faster than the changes seen in the ice core records of past glacial-interglacial cycles. This rapid rate poses significant challenges for ecosystems and species to adapt. A describes a cause of past ice ages, not current warming. B is incorrect; the Earth has been much warmer in its deep past, but the rate of change is the key issue. D is incorrect; current change is not driven by solar activity, and past changes had multiple drivers, including GHGs.
- Which of the following scenarios best illustrates the concept of an ecological tipping point resulting from climate change?
Answer: After years of gradual warming and reduced rainfall, a large portion of a rainforest ecosystem rapidly converts to savanna following a single severe drought.
The correct answer is C. A tipping point is a threshold beyond which a system undergoes a rapid, often irreversible shift to a new state. The sudden conversion of a rainforest to savanna after a period of gradual stress is a classic example. A describes a gradual change, not a rapid shift. B describes a population decline, which may be reversible and is not a system-state change. D describes a seasonal, cyclical, and currently reversible process, not a tipping point.
- Which statement accurately distinguishes between the causes of sea level rise in a warming world?
Answer: The two main causes are the thermal expansion of ocean water as it warms and the melting of land-based ice sheets and glaciers.
The correct answer is B. The two dominant, roughly equal contributors to modern sea level rise are the thermal expansion of water (as water warms, its volume increases) and the addition of new water to the oceans from the melting of land-based ice (e.g., Greenland and Antarctic ice sheets, mountain glaciers). A is a common misconception; the melting of floating sea ice does not significantly change sea level, as the ice was already displacing its own weight in water (Archimedes' principle). C is incorrect; changes in precipitation patterns do not contribute to sea level rise in this way. D is incorrect as it dismisses the very significant contribution from melting land ice.
- Which of the following describes a scenario of carbon sequestration?
Answer: The growth of a large forest, where trees incorporate atmospheric carbon dioxide into their biomass through photosynthesis.
The correct answer is B. Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide. Photosynthesis by plants, especially in a growing forest, removes CO₂ from the atmosphere and stores it as organic carbon in wood, leaves, and roots. A, C, and D all describe processes that release carbon compounds (CO₂ or CH₄) into the atmosphere, which are sources of carbon, not sequestration sinks.
- [HL only] Asynchronous phenological shifts between species can disrupt ecological interactions. Which is the most likely consequence if a flowering plant shifts its flowering time earlier due to warming, but its specialist insect pollinator does not?
Answer: Both the plant and pollinator populations will likely decline due to reproductive failure.
The correct answer is A. This describes a classic case of synchrony disruption. The plant may not be pollinated, leading to reduced seed set and reproductive failure. The specialist pollinator, emerging after the flowers have faded, will have lost its primary food source, leading to starvation and its own reproductive failure. B is too speculative; switching food sources may not be possible for a specialist, and evolving self-pollination is a slow process. C is incorrect as the plant's potential benefit is negated by pollination failure, and the pollinator is directly and negatively affected. D is unlikely; if the species are cued by different things (e.g., temperature for the plant, day length for the insect), they cannot simply choose to re-synchronize.
- [HL only] How is rapid climate change expected to act as a powerful selective pressure on populations of organisms?
Answer: It favours the survival and reproduction of individuals with pre-existing genetic traits that are better suited to the new conditions.
The correct answer is C. This is the core principle of natural selection. Environmental change does not create new traits on demand. Instead, it acts upon the existing variation within a population. Individuals whose inherited traits (e.g., higher heat tolerance, different breeding times) happen to be advantageous in the new climate are more likely to survive and reproduce, passing those traits to the next generation. A describes phenotypic plasticity, not evolution. B is incorrect; mutations are random, not directed by environmental needs. D describes one possible outcome (migration), but the fundamental selective pressure acts on heritable traits related to tolerance of the new climate.
- Increased frequency and intensity of forest fires in boreal regions is an observed effect of climate change that also contributes to it. How does this phenomenon represent a positive feedback cycle?
Answer: Forest fires release large amounts of stored carbon as CO₂, which enhances the greenhouse effect and leads to warmer, drier conditions conducive to more fires.
The correct answer is A. This correctly identifies the positive feedback loop: warming leads to conditions for more fires, the fires release CO₂ (a greenhouse gas), the increased CO₂ leads to more warming, creating a self-reinforcing cycle. B describes a real effect but is a separate feedback loop (ice-albedo), not the primary one involving the fire and atmospheric CO₂. C describes a potential negative feedback, but on the timescale of the fire event and its immediate aftermath, the carbon release far outweighs the subsequent slow uptake. D describes a potential negative feedback (aerosol effect), but the warming effect of the released CO₂ is the dominant long-term climatic impact.
- Climate change poses two distinct threats to coral reefs: coral bleaching and ocean acidification. What is the direct physiological cause of coral bleaching?
Answer: Elevated sea temperatures cause coral polyps to expel their symbiotic zooxanthellae algae, leading to a loss of colour and energy source.
The correct answer is B. Coral bleaching is a specific stress response where prolonged elevated water temperatures cause the breakdown of the symbiosis between corals and their zooxanthellae. The algae are expelled, and the white calcium carbonate skeleton becomes visible. A describes the mechanism of ocean acidification's impact on skeleton formation, which is a different issue. C is incorrect; CO₂ is not directly toxic to the polyps in this manner. D is a potential stressor but is not the direct mechanism of bleaching, which is primarily temperature-driven.
- The ice-albedo feedback is a significant positive feedback mechanism in the climate system. Which statement correctly explains this process?
Answer: Warmer temperatures melt ice, which is highly reflective, exposing darker ocean or land, which absorbs more solar radiation, leading to further warming.
The correct answer is B. Albedo is a measure of reflectivity. Ice and snow have a high albedo (they are very reflective). As temperatures rise and ice melts, it exposes darker surfaces like open ocean or land, which have a low albedo. These darker surfaces absorb more solar radiation, leading to further warming, which in turn melts more ice. This is a classic positive feedback loop. A incorrectly swaps the albedo properties of ice and ocean/land. C describes a different process related to ocean circulation, not the albedo feedback. D is incorrect; ice reflects short-wave radiation, and its removal does not cause a cooling effect in this manner.
- [HL only] The timing of flowering in a certain plant species is determined by the accumulation of 'growing degree days' (a measure of heat). In response to a warmer climate, the species begins to flower earlier in the spring. This is an example of:
Answer: phenotypic plasticity, as the flowering time changes in response to environmental cues without genetic change.
The correct answer is B. Phenotypic plasticity is the ability of one genotype to produce more than one phenotype when exposed to different environments. In this case, the plants' genetic makeup for flowering is not changing, but the environmental cue (heat accumulation) is being met earlier in the year, causing the phenotype (flowering time) to change. A describes an evolutionary change, which might happen over many generations, but the immediate response described is plasticity. C is a mechanism of genetic drift, not the direct explanation for the shift in timing. D is a mode of speciation, which is a much larger-scale outcome than the shift in flowering time for a single species.
- What is the specific role of greenhouse gases in the Earth's energy balance that leads to the greenhouse effect?
Answer: They are transparent to incoming short-wave solar radiation but absorb and re-radiate outgoing long-wave infrared radiation.
The correct answer is C. This accurately describes the mechanism of the greenhouse effect. The sun's energy arrives primarily as short-wave radiation (visible light and UV), which passes through the atmosphere. The Earth's surface absorbs this energy and re-radiates it as long-wave (infrared) radiation. Greenhouse gases absorb this outgoing infrared radiation and re-radiate it in all directions, including back towards the surface, trapping heat. A is incorrect; ozone absorbs UV, but this is not the primary mechanism of the greenhouse effect. B describes the effect of aerosols or clouds, which increase albedo, but not the action of greenhouse gases. D is incorrect; the warming is due to radiative properties, not catalysis of heat-generating reactions.
- A species of alpine plant is adapted to a narrow range of cool temperatures. As the regional climate warms, what is the most likely long-term change in the distribution of this species?
Answer: Its range will shift to higher altitudes on mountains and its overall habitable area will likely contract.
The correct answer is B. Organisms adapted to cool temperatures will need to track their preferred climate. On a mountain, this means moving to higher altitudes where it is cooler. This is an example of a range shift. As the species moves up the mountain, the total available land area typically decreases, leading to range contraction. A suggests a shift to warmer areas, which is incorrect. C incorrectly assumes the CO₂ fertilization effect will override the negative impact of thermal stress. D describes acclimatization, a short-term physiological response of an individual, not a long-term distributional shift of a population or species, and may not be sufficient to cope with significant warming.
- [HL only] A butterfly species has evolved to lay its eggs on a specific host plant just as its leaves emerge in spring. Due to climate change, the plant's leaves are now emerging two weeks earlier on average, but the butterfly's egg-laying cue, day length, has not changed. This situation is best described as:
Answer: a phenological mismatch leading to synchrony disruption.
The correct answer is A. Phenology is the study of the timing of recurring biological events. The plant's leaf emergence and the butterfly's egg-laying are phenological events. Because the plant's timing has shifted in response to temperature cues while the butterfly's has not (being cued by day length), their interaction is now out of sync. This is termed synchrony disruption. B is incorrect as there is no mention of competition. C describes a change in location, not timing. D describes a mode of natural selection, which is not what the scenario is directly illustrating.
- Both methane (CH₄) and carbon dioxide (CO₂) are significant anthropogenic greenhouse gases. Which statement best evaluates their respective contributions to global climate change?
Answer: Carbon dioxide is the dominant driver of climate change because its atmospheric concentration and persistence are much greater than methane's, despite its lower warming potential per molecule.
The correct answer is B. While methane is more potent on a per-molecule basis, carbon dioxide's vastly higher atmospheric concentration and its long residence time (hundreds of years) make it the primary contributor to anthropogenic global warming. A is incorrect because it ignores the crucial role of concentration and persistence. C is incorrect because the balance is not equal; CO₂'s effect is significantly larger. D is incorrect because while water vapour is a powerful greenhouse gas, its atmospheric concentration is primarily a function of temperature (a feedback), not direct anthropogenic emissions, making it a response to, rather than a primary driver of, long-term climate change.
- The thawing of Arctic permafrost is a major concern in climate science as it can initiate a positive feedback loop. Which statement accurately describes the mechanism of this loop?
Answer: Thawing permafrost releases trapped methane, a greenhouse gas, which causes further atmospheric warming, leading to more permafrost thawing.
The correct answer is A. This describes the complete positive feedback cycle: warming -> thawing -> release of greenhouse gases (methane and CO₂) -> more warming -> more thawing. B describes a negative feedback loop, which may occur but is not the primary concern associated with permafrost thaw. C is incorrect because the effect is not merely localized; methane and CO₂ mix globally, contributing to overall warming. D is incorrect as it misidentifies the gases involved and their effects; decomposition does not significantly impact ozone.
