Greenhouse effect and global warming

Correct answer: D. It absorbs outgoing longwave radiation and strengthens the greenhouse effect

Explanation: The correct answer is D. Earth’s surface emits energy as longwave radiation, and carbon dioxide absorbs some of it and re-emits it in different directions. This contributes to the greenhouse effect; an increase in carbon dioxide can strengthen this warming effect. Nitrogen, not carbon dioxide, is the most abundant atmospheric gas, and condensation nuclei are usually tiny particles such as dust or sea salt.

Correct answer: C. It is a trace greenhouse gas

Explanation: The correct answer is C. Methane is present in the atmosphere in much smaller amounts than nitrogen and oxygen, so it is a trace gas. Even at low concentrations, it absorbs some of the infrared radiation leaving Earth and contributes to the greenhouse effect. Nitrogen is the most abundant gas in dry air, and oxygen is used in respiration; methane is not a condensation nucleus.

Correct answer: C. Argon — photosynthesis

Explanation: The correct answer is C. Argon is a largely unreactive gas and is not used by plants for photosynthesis. Plants use carbon dioxide, water and light energy to make food. Oxygen is used in aerobic respiration, ozone absorbs much ultraviolet radiation in the atmosphere, and carbon dioxide contributes to the greenhouse effect, so those matches are correct.

Correct answer: A. It is involved in cloud formation and rainfall, and it contributes to the greenhouse effect.

Explanation: Answer: A. Water vapour can condense into tiny droplets or ice crystals to form clouds, and precipitation may follow. It also absorbs some outgoing infrared radiation, contributing to the greenhouse effect. These roles connect it to weather and climate.

Correct answer: A. The role of the same gas can differ according to its amount and context

Explanation: A is correct. Plants use carbon dioxide in photosynthesis to make sugars. But carbon dioxide is also a greenhouse gas that absorbs some of the heat Earth radiates outward. When its atmospheric concentration increases, it can contribute to global warming. Thus, a substance can be useful in one process and have a harmful effect when its amount or context changes.

Correct answer: C. It absorbs outgoing infrared radiation and contributes to the greenhouse effect

Explanation: C is correct. Methane (CH₄) is much less abundant than nitrogen and oxygen, but it absorbs some outgoing infrared radiation from Earth and contributes to the greenhouse effect. Its low concentration therefore does not mean it has no climate impact.

Correct answer: A. Plants use it to make food

Explanation: A is correct. Plants use carbon dioxide, water, and light energy in photosynthesis to make sugars and other organic substances, releasing oxygen as a by-product. CO₂ therefore has an essential role in plant life and is not only a pollutant. However, excess CO₂ from human activities strengthens the greenhouse effect and contributes to global warming.

Correct answer: A. Because the natural effect maintains a habitable temperature, whereas enhancement can increase climate risk

Explanation: Direct answer: A is correct. The natural greenhouse effect is a normal physical process. Certain gases absorb and re-emit some of Earth’s outgoing infrared energy, helping keep the surface and lower atmosphere warm enough for life. Without this natural effect, Earth would be much colder. The enhanced greenhouse effect refers to the additional warming influence produced when human activities increase the concentration of greenhouse gases, such as carbon dioxide, methane and nitrous oxide. This can disturb the energy balance and increase climate-related risks. B is wrong because the natural effect is useful but its enhancement can be harmful. C is wrong because the greenhouse effect is a real atmospheric process. D is wrong because nitrogen gas is not the main greenhouse gas described here. The key distinction is natural baseline versus human-driven strengthening. Memory cue: natural greenhouse effect makes Earth habitable; enhanced greenhouse effect adds warming pressure.

Correct answer: A. Trend of global warming

Explanation: Option A is correct because carbon dioxide is a greenhouse gas that absorbs outgoing infrared radiation and re-emits part of that energy, strengthening heat retention in the atmosphere. A sustained rise can therefore contribute to a long-term warming trend, although climate is influenced by several factors. It does not immediately remove nitrogen, burn argon, or convert ozone into rain.

Correct answer: C. Because it is a greenhouse gas that absorbs outgoing infrared radiation

Explanation: Correct answer: C. Methane is present at a much lower concentration than the main atmospheric gases, but its molecules absorb some of the infrared radiation emitted by Earth. This makes methane a greenhouse gas that contributes to the greenhouse effect, so it matters in climate studies despite its small concentration.

Correct answer: A. Global climatic

Explanation: Direct answer: A, global climatic. Carbon dioxide is a greenhouse gas that can remain in the atmosphere for a long time and become widely mixed. As its concentration increases, it can alter Earth’s energy balance by affecting the outgoing and incoming radiation system. This can contribute to warming and climate change across regions, so the concern is not limited to the place where the gas was emitted. Option A is correct. Option B is wrong because soil colour is not the principal reason rising carbon dioxide is globally important. Option C is wrong because river flow may be influenced indirectly by climate, but it does not describe the main effect. Option D is wrong because mountain height is not the direct global consequence of increased carbon dioxide. Memory cue: a widely mixed greenhouse gas can create a worldwide climate effect.

Correct answer: A. Longwave terrestrial radiation

Explanation: After absorbing incoming shortwave solar energy, Earth's surface emits energy mainly as longwave terrestrial or infrared radiation. Greenhouse gases absorb selected wavelengths of this outgoing radiation and re-emit energy in different directions, including back toward the surface. This radiative process is the physical basis of the greenhouse effect.

Correct answer: B. They are different processes, but some gases may be associated with both

Explanation: Ozone depletion is the reduction of stratospheric ozone, which weakens protection from harmful ultraviolet radiation. Global warming is the long-term rise in average temperature caused mainly by increased greenhouse gases. These are different atmospheric processes, although substances such as CFCs can damage ozone and also act as powerful greenhouse gases.

Correct answer: A. Rainfall irregularity may increase in some areas

Explanation: Global warming changes evaporation, atmospheric moisture-holding capacity, circulation patterns, and the timing of storms. Consequently, some regions may experience heavier short-duration rainfall, while others may face longer dry periods or altered monsoon timing. The effect is not uniform everywhere, so warming does not mean that rainfall will stop or become identical each day.

Correct answer: A. They can both trap some heat and reflect some sunlight

Explanation: Clouds have competing effects on Earth’s energy balance. They can reflect incoming sunlight back to space, producing a cooling effect, while also absorbing and re-emitting outgoing infrared radiation, producing a warming effect. The net effect depends on cloud type, altitude, thickness, and location. Option A is correct.

Correct answer: A. Because climate is understood through long-term averages

Explanation: Weather can change from day to day, whereas climate describes long-term patterns and averages of temperature, rainfall, and other conditions. Long records help scientists separate ordinary variability from persistent trends, detect changes in extremes, and compare present conditions with the past. Therefore, option A is correct.

Correct answer: A. Earth's energy balance can be disturbed

Explanation: Excess greenhouse gases absorb more of Earth’s outgoing longwave, or infrared, radiation and re-emit part of it within the atmosphere. This changes the balance between incoming solar energy and outgoing terrestrial energy, so the energy balance is disturbed and the surface and lower atmosphere tend to warm. They do not stop incoming sunlight or alter Earth’s orbit.

Correct answer: A. Changes in rainfall patterns and extreme weather events

Explanation: Warming changes the temperature of the atmosphere and oceans, affecting evaporation, moisture transport and circulation. Consequently, rainfall patterns may shift and heat waves, droughts, intense rainfall and some storms may become more frequent or severe. It does not directly change Earth's rotation or the Moon's colour.

Correct answer: A. Carbon dioxide

Explanation: Carbon dioxide is a long-lived greenhouse gas: a portion of an emission can remain in the atmosphere for centuries or longer, although it is continuously exchanged with oceans, vegetation and soils. Water vapour is also a greenhouse gas, but its atmospheric residence time is usually much shorter because it condenses and precipitates.

Correct answer: B. Process of trapping heat in the atmosphere

Explanation: The greenhouse effect is the warming produced when gases in the atmosphere absorb and re-radiate part of the infrared radiation emitted by Earth’s surface. This natural process keeps the planet warm enough for life. A human-caused increase in greenhouse gases strengthens the natural effect and contributes to global warming.

Correct answer: A. Burning more coal and oil

Explanation: Coal and oil are fossil fuels. Burning them for electricity, transport, or industry releases large quantities of carbon dioxide, a long-lived greenhouse gas. The increased concentration of this gas absorbs more outgoing infrared radiation and raises the average temperature of Earth. The other processes are not the principal direct human cause.

Correct answer: C. Carbon dioxide

Explanation: Carbon dioxide is a major greenhouse gas whose concentration increases through burning coal, oil, and gas, deforestation, cement manufacture, and several industrial activities. It absorbs outgoing infrared radiation and contributes to warming. Oxygen and nitrogen dominate the atmosphere but do not act as important greenhouse gases, while argon is largely inert.

Correct answer: D. Atmospheric carbon dioxide

Explanation: Forests remove carbon dioxide from the atmosphere through photosynthesis and store carbon in living biomass and soils. Deforestation reduces this carbon-sink capacity and may also release stored carbon when trees are burned or decay. Consequently, atmospheric carbon dioxide can increase, strengthening the greenhouse effect and contributing to global warming.

Correct answer: A. Protecting Earth from extreme cold

Explanation: The natural greenhouse effect absorbs and re-radiates some infrared energy, preventing Earth from losing all of its heat to space. Without it, the planet’s average surface temperature would be far lower and liquid water and life would be much more difficult to sustain. The problem is the human-enhanced increase, not the natural effect itself.

Correct answer: D. It absorbs infrared heat and helps retain warmth

Explanation: Water vapor is the most abundant natural greenhouse gas. It absorbs some infrared radiation emitted by Earth and re-radiates energy in different directions, helping retain warmth in the lower atmosphere. Its amount is strongly controlled by temperature, so warming can increase evaporation and create a feedback that produces further warming.