Question
Which gas is the main contributor to the greenhouse effect?
A. Ozone
B. Methane
C. Nitrogen oxide
D. Water vapour
▶️Answer/Explanation
Answer: D. Water vapour
Explanation:
- The greenhouse effect is caused by gases in the atmosphere that trap heat radiated from Earth’s surface, keeping the planet warm. These gases absorb and re-emit infrared radiation.
- Water vapour is the most abundant and most effective greenhouse gas. It contributes more to the natural greenhouse effect than any other gas by retaining heat in the atmosphere.
- While gases like methane and nitrogen oxide are stronger per molecule, they are present in much smaller amounts compared to water vapour.
Answer Evaluation:
A. Incorrect – Ozone absorbs UV radiation but is not a major contributor to the greenhouse effect.
B. Incorrect – Methane is a potent greenhouse gas but contributes less overall than water vapour due to lower concentration.
C. Incorrect – Nitrogen oxide contributes to the greenhouse effect but is less significant than water vapour.
D. Correct – Water vapour is the main contributor to the greenhouse effect due to its abundance and strong heat-trapping ability.
Question
Which activity directly contributes the most to recent increases in atmospheric CO2 concentrations?
A. Landfills
B. Planting trees
C. Cattle rearing
D. Burning of fossil fuels
▶️Answer/Explanation
Answer: D. Burning of fossil fuels
Explanation:
- The recent increase in atmospheric carbon dioxide (CO₂) is mainly due to human activities that release large amounts of CO₂. The burning of fossil fuels like coal, oil, and natural gas for energy and transportation is the largest source.
- This process releases carbon stored underground for millions of years, rapidly increasing CO₂ levels in the atmosphere and contributing to global warming.
- Other activities like landfills and cattle rearing release greenhouse gases but contribute less to CO₂ increases. Planting trees actually reduces atmospheric CO₂ by absorbing it.
Answer Evaluation:
A. Incorrect – Landfills release methane, a greenhouse gas, but not the largest source of CO₂.
B. Incorrect – Planting trees removes CO₂ from the atmosphere, not adds to it.
C. Incorrect – Cattle rearing produces methane, not CO₂, and is a smaller contributor to CO₂ levels.
D. Correct – Burning fossil fuels is the main cause of recent increases in atmospheric CO₂.
Question
The oceans absorb much of the carbon dioxide in the atmosphere. The combustion of fossil fuels has increased carbon dioxide ocean concentrations. What adverse effect does this have on marine life?
Heterotrophs consume more phytoplankton.
Phytoplankton have increased rates of photosynthesis.
Corals deposit less calcium carbonate to form skeletons.
Increased pH reduces enzyme activity in marine organisms.
Answer/Explanation
Answer: C. Corals deposit less calcium carbonate to form skeletons
Explanation:
- When carbon dioxide (CO₂) dissolves in ocean water, it forms carbonic acid, which lowers the ocean’s pH, causing ocean acidification.
- Acidic conditions reduce the availability of carbonate ions, which are essential for corals and other marine organisms to produce calcium carbonate—the material needed to build their skeletons and shells.
- As a result, corals have difficulty forming strong skeletons, affecting coral reef health and marine biodiversity.
Answer Evaluation:
A. Heterotrophs consuming more phytoplankton – Incorrect; this is not a direct effect of increased CO₂ in oceans.
B. Phytoplankton increased photosynthesis – Incorrect; acidification generally harms marine organisms rather than boosting photosynthesis.
C. Corals deposit less calcium carbonate – Correct; acidification reduces carbonate ion availability needed for skeleton formation.
D. Increased pH reduces enzyme activity – Incorrect; increased CO₂ lowers pH (makes it more acidic), not increases it.
Question
The table shows features of greenhouse gases in the atmosphere.
According to the data in the table, which greenhouse gas contributes the most to climate change?
A. Carbon dioxide because it is the most abundant greenhouse gas
B. Methane because it has the shortest lifespan
C. Nitrous oxides because they absorb the greatest amount of shortwave radiation
D. CFCs because they destroy the ozone layer
▶️Answer/Explanation
Answer: A. Carbon dioxide because it is the most abundant greenhouse gas
Explanation:
- The impact of a greenhouse gas on climate change depends on both its concentration in the atmosphere and its lifespan.
- Carbon dioxide (CO₂) is the most abundant greenhouse gas listed, with a concentration of 397 ppm, and it remains in the atmosphere for a long time (50–200 years).
- This makes CO₂ the largest contributor to climate change because it accumulates and persists, trapping heat over a long period.
- Although gases like methane are more potent per molecule, their much lower concentrations and shorter lifespans reduce their overall impact.
- Nitrous oxides and CFCs have smaller concentrations and different environmental effects (like ozone depletion), so they contribute less to climate warming according to the data.
Answer Evaluation:
A. Correct – CO₂’s high concentration and long lifespan make it the biggest contributor to climate change.
B. Incorrect – Methane is potent but less abundant and short-lived.
C. Incorrect – Nitrous oxides have low concentration and the table does not focus on radiation absorption.
D. Incorrect – CFCs destroy ozone but are not the main cause of climate change here.