Greenhouse effect and global warming

As mean sea level rises, low-lying coastal land is more easily inundated. High tides, storm surges and cyclones can therefore cause coastal floods more frequently and over larger areas. Sea-level rise may also accelerate erosion and saltwater intrusion, but it does not form mountain ranges or remove air from the atmosphere. Thus increased coastal flooding is the direct result.

Using less electricity through efficient appliances, switching off unused lights and improving insulation can reduce the amount of power that must be generated. Where electricity comes partly from fossil fuels, lower demand leads to lower carbon dioxide emissions. Keeping lights on, burning waste and unnecessary car use generally increase energy use or pollution rather than reducing household emissions.

The large-scale use and combustion of coal, petroleum and natural gas releases carbon dioxide, while extraction and distribution can also release methane. These greenhouse gases enhance heat retention and are the dominant human influence on recent global warming. Tree shade, river flow and mountain height affect local conditions but are not human activities that drive the global trend.

Methane, CH4, is a greenhouse gas that absorbs infrared radiation and contributes to atmospheric heat retention. It is emitted by sources such as livestock digestion, wetlands, landfills, rice cultivation and fossil-fuel operations. Although its atmospheric concentration is lower than carbon dioxide’s, methane has strong warming potential over relevant time periods, so it is not an inert or rare gas.

Waterlogged paddy fields contain very little oxygen. Microorganisms decompose organic matter under these anaerobic conditions and release methane. Methane is a potent greenhouse gas, so flooded rice cultivation is an important agricultural source of climate-warming emissions. Therefore, option A is correct.

When organic material decomposes without sufficient oxygen, microorganisms can produce methane. This occurs in wetlands, landfills, manure, and other oxygen-poor environments. Methane is a powerful greenhouse gas. Although carbon dioxide may also form during some decomposition, methane is the intended answer here.

Trees absorb carbon dioxide during photosynthesis and store carbon in their trunks, leaves, roots, and surrounding soil. Increasing tree cover can therefore remove some CO₂ from the atmosphere. In contrast, petrol use, open burning, and idling vehicles consume fuel and increase emissions.

Energy efficiency means obtaining the same useful service or performing the same task with less energy. For example, an efficient appliance may use less electricity, and an efficient vehicle may use less fuel for the same distance. If the saved energy would otherwise have been produced by burning coal, oil, or natural gas, lower fuel consumption generally reduces carbon dioxide and other greenhouse-gas emissions. This helps slow global warming, although the actual reduction depends on the energy source and total demand. Therefore, option A is correct; the extreme claims in options B, C, and D are scientifically false.

Climate warming contributes to sea-level rise through the thermal expansion of seawater and the melting of land-based glaciers and ice sheets. Higher seas increase coastal flooding, erosion, saltwater intrusion, and storm-surge damage. Thus, sea-level rise is a major climate risk for low-lying coastal regions.

An enhanced greenhouse effect warms the atmosphere and oceans and can alter rainfall, circulation, and evaporation patterns. These changes may increase the frequency or intensity of heat waves, heavy rainfall, droughts, and severe storms in different regions. Therefore, extreme weather is the appropriate answer.

Saving electricity reduces the demand for power generation. In many regions, electricity is partly produced by burning coal, oil, or natural gas, which releases carbon dioxide. Turning off unused lights and appliances, using efficient devices, and avoiding waste are simple household actions that can lower emissions.

Solar, wind, and hydropower produce energy without directly burning coal, petroleum, or natural gas. Replacing fossil-fuel use with renewable energy can therefore reduce carbon dioxide and other greenhouse-gas emissions. The effect depends on the full energy system, but lower emissions are the intended benefit in this question.

A higher sea level allows seawater to reach low-lying coastal land more easily. Flooding becomes especially dangerous during high tides, storm surges, cyclones, and heavy rainfall. Sea-level rise is associated with warming oceans and melting land ice, whereas the other options do not directly explain the general increase in coastal-flood risk.

Flooded rice paddies become oxygen-poor environments. Anaerobic microorganisms break down plant residues and soil organic matter there, producing methane that escapes into the atmosphere through water, soil, and rice plants. Thus, methane is the characteristic greenhouse gas associated with conventional waterlogged paddy cultivation.

Trees remove carbon dioxide from the atmosphere during photosynthesis and store carbon in their biomass and soils. Planting suitable trees can therefore support carbon sequestration, provide shade, improve habitats, and help moderate local temperatures. The amount stored depends on species, growth, soil, and long-term management.

Controlling emissions slows the accumulation of greenhouse gases such as carbon dioxide, methane, and nitrous oxide in the atmosphere. With fewer heat-trapping gases, the additional warming pressure on the climate system is reduced. Emission control is therefore a key mitigation strategy, though it does not stop natural rainfall or other processes.

Renewable energy from sources such as sunlight and wind can replace electricity or heat produced by burning coal, oil, and gas. This reduces associated carbon dioxide emissions and supports climate mitigation. Other options waste fuel or directly add pollution and greenhouse gases, so adopting renewable energy is the only suitable climate solution listed.

Reducing unnecessary electricity use lowers demand on power stations. Where electricity is generated with coal, oil, or gas, this can reduce fuel combustion and carbon dioxide emissions. Switching off unused lights, choosing efficient appliances, and avoiding standby waste are simple household actions. The other choices increase energy use or pollution.

Renewable energy sources such as solar, wind, and hydropower generally produce electricity with far lower greenhouse-gas emissions than coal, oil, or natural gas. Replacing fossil-fuel-based generation reduces carbon dioxide emissions and often reduces other air pollutants as well. This helps slow the increase in radiative forcing and supports efforts to limit global warming. Renewable energy does not cause an immediate rise in global temperature. Therefore, the most appropriate climate impact is the reduction of greenhouse-gas emissions in option A.

Industrialisation greatly increased the burning of coal, petroleum and natural gas for electricity, transport and manufacturing. This released large quantities of carbon dioxide, while agriculture and industry added methane and nitrous oxide. The resulting rise in greenhouse-gas concentrations increased heat retention and global warming.

Human activities, especially burning coal, oil and gas, cement production, deforestation and some agricultural practices, increase greenhouse-gas concentrations. These gases reduce the loss of outgoing infrared energy and create a positive energy imbalance. That human-driven increase is the direct cause of present global warming, not a sudden change in latitude or gravity.

Carbon dioxide, methane and nitrous oxide all absorb portions of Earth’s outgoing infrared radiation. By reducing the rate at which heat escapes to space, they contribute to the greenhouse effect and can cause warming when their atmospheric concentrations rise. They are not inert gases, ozone-producing gases as a group, or a recognised class called rain gases.

A is correct. Climate-change mitigation means reducing greenhouse-gas emissions or protecting carbon stores. Replacing coal, oil and gas with low-emission energy sources such as solar or wind can reduce carbon dioxide emissions from energy production. The other choices increase emissions or reduce carbon-absorbing vegetation.

The correct answer is A. Global warming means a sustained increase in Earth’s average surface temperature. It is mainly driven by the enhanced greenhouse effect as human activities increase the amount of heat-trapping gases in the atmosphere.

The natural greenhouse effect occurs when gases such as water vapour, carbon dioxide, and methane absorb and re-radiate some outgoing infrared energy. This keeps Earth considerably warmer than it would be without an atmosphere, allowing liquid water and life to exist. The problem is not the natural effect itself but its human-driven intensification.