Climate change practice questions.

Which gas is the largest single contributor to the anthropogenic enhanced greenhouse effect, largely due to the combustion of fossil fuels?

• Oxygen (O2)
• Carbon dioxide (CO2)
• Nitrogen (N2), unreactive
• Ozone (O3)

Answer: Carbon dioxide (CO2)

CO2 released by burning fossil fuels is the dominant anthropogenic greenhouse gas. Nitrogen and oxygen are not greenhouse gases as they do not absorb infrared strongly.

Explain how greenhouse gases warm the Earth's surface.

• They prevent short-wave solar radiation from reaching the Earth's surface
• They absorb and re-emit long-wave (infrared) radiation emitted by the Earth's surface
• They increase the amount of ultraviolet radiation entering the atmosphere
• They chemically react with the surface to release heat directly

Answer: They absorb and re-emit long-wave (infrared) radiation emitted by the Earth's surface

Greenhouse gases are largely transparent to incoming short-wave solar radiation but absorb the long-wave infrared re-radiated by the warmed surface, then re-emit it in all directions, warming the lower atmosphere.

A study finds that atmospheric CO2 concentration and mean global temperature have risen together over the past century. Which statement is the most scientifically cautious interpretation?

• The correlation alone proves CO2 causes warming with no further evidence needed
• Correlation plus a known mechanism is evidence CO2 adds to warming
• Correlation shows the two variables are completely unrelated
• Temperature must be causing the rise in CO2, not the reverse

Answer: Correlation plus a known mechanism is evidence CO2 adds to warming

Correlation alone does not establish causation, but when a robust correlation is combined with an established physical mechanism (infrared absorption by CO2), it constitutes strong evidence for a causal link.

Ocean acidification is a consequence of rising atmospheric CO2. Which explanation is correct?

• CO2 dissolves forming carbonic acid, lowering ocean pH
• CO2 raises ocean pH by forming hydroxide ions
• CO2 has no chemical effect on seawater, only a thermal one
• CO2 increases carbonate ion availability for shell-building organisms

Answer: CO2 dissolves forming carbonic acid, lowering ocean pH

Dissolved CO2 reacts with water to form carbonic acid, which dissociates to release H+ ions, lowering pH and reducing carbonate availability for organisms that build calcium carbonate shells and skeletons.

Coral bleaching linked to rising sea temperatures occurs because:

• Corals grow a thicker calcium carbonate skeleton that hides their colour
• Heat stress makes corals expel their zooxanthellae, losing colour and energy
• Increased warmth allows zooxanthellae to multiply rapidly, darkening the coral
• Corals migrate to deeper water and lose pigment

Answer: Heat stress makes corals expel their zooxanthellae, losing colour and energy

Under thermal stress corals expel the symbiotic algae (zooxanthellae) that give them colour and supply much of their energy via photosynthesis, leaving the white skeleton visible and threatening coral survival.

As spring temperatures rise earlier each year, some insect pollinators emerge before the plants they pollinate flower. This mismatch is best described as:

• Convergent evolution
• Phenological mismatch
• Genetic drift
• Density-dependent competition

Answer: Phenological mismatch

Phenology is the timing of seasonal biological events. Climate change can shift the timing of emergence and flowering unequally, producing a mismatch that disrupts pollination and food webs.