Greenhouse effect and global warming

Correct answer: A. The greenhouse effect is natural, but human activities can increase it

Explanation: The natural greenhouse effect is an essential process: gases such as water vapour, carbon dioxide, and methane retain some outgoing infrared heat and keep Earth suitable for life. Human activities can raise greenhouse-gas concentrations, strengthening this effect and causing additional warming. Thus, the natural process is not itself wholly harmful.

Correct answer: A. Carbon dioxide absorption from the atmosphere increases

Explanation: During photosynthesis, trees absorb carbon dioxide from the atmosphere and use carbon to form leaves, wood, roots, and other biomass. Planting and protecting trees therefore strengthens a natural carbon sink and can help reduce the growth of atmospheric CO2, although it cannot by itself solve all climate-change problems. Thus, option A is correct.

Correct answer: A. It helps limit global warming

Explanation: Emission control limits the release of greenhouse gases such as carbon dioxide, methane, and nitrous oxide from vehicles, industries, electricity generation, and agriculture. Slowing the accumulation of these gases reduces additional heat trapping and helps limit global warming. It does not stop rainfall or produce the other effects listed, so A is correct.

Correct answer: B. Long term and global

Explanation: Climate change refers to persistent changes in average temperature, rainfall, winds, and other climate patterns over decades or longer. Because greenhouse gases and their effects spread through the atmosphere and influence regions worldwide, climate change is both long-term and global rather than merely local, seasonal, or daily. Therefore, B is correct.

Correct answer: A. Emissions of greenhouse gases and air pollutants

Explanation: Combustion of petrol or diesel in vehicle engines releases carbon dioxide, carbon monoxide, nitrogen oxides, hydrocarbons, and fine particulate matter. These substances contribute to air pollution, while carbon dioxide is also a greenhouse gas. Rain, dew, and snowfall form through atmospheric conditions, not directly from vehicle smoke. Thus A is correct.

Correct answer: A. Energy saving can reduce fossil-fuel burning and greenhouse-gas emissions

Explanation: Using less energy through efficient appliances, insulation, public transport, and careful consumption can reduce the amount of coal, petroleum, and natural gas burned. Lower fossil-fuel combustion generally means lower carbon dioxide emissions and less additional heat trapping. Energy saving does not alter incoming solar energy or create oceans, so A is correct.

Correct answer: A. Protecting trees

Explanation: Healthy trees remove carbon dioxide from the atmosphere through photosynthesis and store carbon in trunks, roots, leaves, soils, and forest biomass. Protecting existing forests prevents this carbon store from being lost and avoids emissions from deforestation. Burning plastic or using more diesel has the opposite effect. Therefore, option A is correct.

Correct answer: A. Carbon dioxide

Explanation: Industrial fuel combustion releases carbon dioxide, while cement manufacture releases additional CO2 during the chemical conversion of limestone to clinker. Construction also uses energy-intensive materials and transport systems that commonly depend on fossil fuels. Although some industries can emit methane, carbon dioxide is the principal gas associated with the processes described. Therefore, A is correct.

Correct answer: A. Greenhouse gas

Explanation: Carbon dioxide is a greenhouse gas because it absorbs selected wavelengths of outgoing infrared radiation from Earth and re-emits energy within the atmosphere. This natural property helps keep Earth warm, but increased CO2 from human activities strengthens the greenhouse effect and contributes to global warming. It is not an inert gas, metallic gas, or solid. Therefore, A is correct.

Correct answer: A. Using public transport

Explanation: A bus, metro, or train can carry many passengers using less fuel per person than numerous separate private vehicles. This lowers fuel consumption and usually reduces carbon dioxide and other emissions per passenger, especially when the system is well used and efficiently operated. Idling, solo driving, and open burning generally increase emissions. Hence A is correct.

Correct answer: A. Burning fossil fuels

Explanation: Burning coal, oil, and natural gas for electricity, transport, heating, and industry releases large quantities of carbon dioxide and other greenhouse gases. These gases increase the atmosphere’s capacity to retain outgoing heat and are the principal human cause of current global warming. Mountain formation, day length, and cloud clearing are not the best examples of human-caused warming. Thus A is correct.

Correct answer: A. By increasing the absorption of atmospheric carbon dioxide

Explanation: Through photosynthesis, growing trees remove carbon dioxide from the air and store carbon in wood, roots, leaves, litter, and soil. Planting trees can therefore increase biological carbon uptake, while protecting them prevents the release of stored carbon. It is not a method for stopping winds or directly increasing ocean evaporation. Thus, option A is correct.

Correct answer: A. Rise in global average temperature

Explanation: Greenhouse gases absorb part of Earth’s outgoing infrared radiation. When their concentration increases excessively, the atmosphere retains more energy, producing a positive radiative imbalance and raising global average temperature. This enhanced greenhouse effect drives global warming and related climate changes. It does not convert seawater to freshwater or remove the atmosphere, so A is correct.

Correct answer: A. Adopting renewable energy

Explanation: Solar, wind, hydropower, and other renewable sources can generate electricity without the direct combustion of coal, oil, or natural gas. Replacing fossil-fuel energy with renewables can therefore reduce carbon dioxide emissions, although manufacturing, construction, and backup systems still have some life-cycle impacts. Coal use, vehicle smoke, and open burning generally increase emissions. Thus A is correct.

Correct answer: A. Planting trees

Explanation: Trees absorb atmospheric carbon dioxide during photosynthesis and store the resulting carbon in biomass and soils. Afforestation, reforestation, and forest conservation can therefore increase carbon removal or prevent emissions from deforestation. Burning coal, burning waste, and increasing vehicle use generally release more CO2 and other pollutants. Hence, planting trees is the correct answer, A.

Correct answer: A. Energy saving can reduce fossil-fuel use and greenhouse-gas emissions

Explanation: Energy conservation reduces the demand for electricity, transport fuel, heating, and industrial energy. Where these services are supplied by fossil fuels, lower demand means less combustion and fewer greenhouse-gas emissions, especially carbon dioxide. It does not increase emissions or directly raise Earth’s heat. Therefore, option A correctly describes energy saving as climate-change mitigation.

Correct answer: A. Coastal flooding

Explanation: A rise in sea level increases the likelihood that low-lying coastal areas will be inundated. High tides, storm surges and cyclones can then produce more frequent and severe flooding. Coastal flooding may damage homes, farmland, roads and freshwater supplies, whereas the other options are not direct consequences of rising sea level.

Correct answer: B. Use of renewable energy

Explanation: Using renewable energy from sources such as sunlight, wind and flowing water can replace electricity generated from coal, oil or gas. This reduces carbon dioxide emissions and other pollutants over time. The remaining choices increase fuel consumption or pollution, so they cannot be suitable general measures for climate-change mitigation.

Correct answer: A. Carbon dioxide

Explanation: Carbon dioxide is an important greenhouse gas because it absorbs outgoing infrared radiation and helps retain heat in the lower atmosphere. Human activities such as burning coal, petroleum and natural gas have increased its concentration substantially. Sand, iron and salt are not atmospheric greenhouse gases and do not produce this effect.

Correct answer: A. Burning fossil fuels

Explanation: Burning coal, petroleum and natural gas releases large quantities of carbon dioxide and other greenhouse gases. These gases absorb outgoing infrared radiation, strengthening the enhanced greenhouse effect and raising average global temperature. Cloud formation, river flow and ordinary rock breaking are natural processes, but they are not the principal human cause of current global warming.

Correct answer: A. Combustion of fossil fuels

Explanation: Combustion of coal, petroleum and natural gas combines carbon with oxygen and releases carbon dioxide. Vehicles, factories and thermal power stations therefore form major human sources of increasing atmospheric CO2. Sea waves, clouds and rainfall belong mainly to physical processes of the ocean and water cycle and are not comparable sources of human carbon emissions.

Correct answer: A. Rise in sea level

Explanation: Land glaciers and ice sheets store freshwater above sea level. When they melt, part of this water flows into the oceans and contributes to sea-level rise. Melting also changes regional water supplies and can affect ecosystems, but it does not normally change Earth’s rotation direction or immediately alter the length of a day. Thus option A is the direct general result.

Correct answer: A. Coastal flooding

Explanation: Higher sea levels allow ordinary high tides and storm surges to reach farther inland. As a result, coastal flooding becomes more frequent and severe, especially in low-lying deltas, islands and densely settled shores. It can damage infrastructure, contaminate freshwater with salt and displace people. Mountain formation and changes in day length are unrelated processes.

Correct answer: A. Helping reduce greenhouse-gas emissions

Explanation: Solar, wind and hydropower can generate energy without directly burning coal, oil or natural gas. Replacing fossil-fuel use with these lower-carbon sources can reduce carbon dioxide emissions and air pollution, although their full environmental effects still require responsible planning. The other choices describe harmful outcomes, not benefits of renewable energy.

Correct answer: A. Lower per-person emissions

Explanation: Carpooling allows several people travelling in the same direction to share one vehicle. Compared with each person using a separate car, it can reduce the number of vehicle trips, fuel consumption and greenhouse-gas emissions per passenger. The exact saving depends on distance and occupancy, but the general environmental benefit is lower per-person emissions.