Greenhouse effect and global warming

Water vapour is a naturally occurring greenhouse gas. Its molecules absorb outgoing infrared radiation emitted by Earth’s surface and re-emit energy in different directions, including back toward the surface. This helps retain atmospheric warmth. Nitrogen, oxygen, and argon are abundant gases but do not significantly absorb infrared radiation in this way.

The greenhouse effect is comparable to a blanket because greenhouse gases allow most incoming sunlight to enter but absorb part of the outgoing infrared radiation from Earth. This reduces heat loss and keeps the lower atmosphere warmer. A fan circulates air, ice cools its surroundings, and a clock has no role in heat retention.

Water vapour is naturally present in the atmosphere and is the most abundant natural greenhouse gas. It absorbs outgoing infrared radiation and contributes to the natural greenhouse effect that keeps Earth warm enough for life. Sodium, iron, and copper are elements, not atmospheric greenhouse gases under ordinary conditions.

Human-induced warming is a major part of anthropogenic climate change. Burning coal, oil, and gas, deforestation, agriculture, and industrial activities increase greenhouse gases, especially carbon dioxide and methane. These gases strengthen heat retention and alter climate patterns. Lunar eclipses, tides, and mountain building do not explain this long-term atmospheric warming.

The greenhouse effect is the natural atmospheric process in which gases such as water vapour, carbon dioxide, methane, and nitrous oxide absorb part of Earth’s outgoing infrared radiation. Re-radiation of this energy helps retain heat near the surface. Ozone depletion concerns ultraviolet protection, while weathering and erosion are surface processes.

Saving energy reduces the demand for electricity and fuels. Where power or transport depends on coal, oil, or natural gas, lower energy use means less fuel combustion and fewer carbon dioxide emissions. The other choices increase energy consumption or fossil-fuel burning, so they generally increase the carbon footprint rather than reduce it.

An LED bulb produces comparable illumination while using much less electricity than an incandescent bulb and often less than older fluorescent lighting. Lower electricity use for the same service means higher energy efficiency and usually lower emissions. The other choices waste energy, increase pollution, or do not represent efficient performance.

Public transport carries many passengers in one vehicle, so fuel consumption and carbon dioxide emissions per passenger are generally lower than when each person travels alone by car. Idling wastes fuel without moving the vehicle, speeding often increases fuel use, and solo driving usually produces more emissions per traveller. Thus public transport is the best answer.

Methane is strongly associated with agriculture because ruminant animals release it during enteric fermentation and flooded rice fields produce it under oxygen-poor conditions. Agriculture also emits nitrous oxide from fertilised soils, so the wording refers to the commonly highlighted gas rather than the only agricultural greenhouse gas. Argon is not a greenhouse gas of agricultural significance.

Statement D is incorrect because greenhouse gases absorb and re-emit some of Earth’s outgoing infrared radiation, thereby retaining heat in the lower atmosphere. Carbon dioxide and water vapour are both greenhouse gases, and global warming means a long-term rise in average temperature. The word “never” makes D scientifically false.

Burning fossil fuels releases large quantities of carbon dioxide and other greenhouse gases. Increased concentrations absorb more outgoing infrared radiation, strengthen the greenhouse effect, and disturb Earth’s energy balance. Large-scale tree planting and efficient appliances can reduce emissions, while rainwater harvesting conserves water and does not increase atmospheric warming.

Option A contains carbon dioxide, methane, and water vapour, all of which absorb infrared radiation and contribute to the greenhouse effect. Oxygen, nitrogen, and argon are major atmospheric gases but are not significant greenhouse gases in ordinary atmospheric conditions. The substances in C and D are solid elements or materials, not atmospheric gases.

Melting ice is a visible indicator of unusually high temperatures or a long-term warming trend. Warmer air and oceans can accelerate the loss of glaciers, snow cover, and sea ice, contributing to sea-level rise in the case of land ice. Glacier expansion and falling average temperature generally indicate cooling, not excess heat.

The strength of the greenhouse effect depends mainly on the concentration and radiative properties of greenhouse gases such as carbon dioxide, methane, water vapour, and nitrous oxide. These gases absorb outgoing infrared radiation and re-radiate part of it. Salinity, rock colour, and tree height can affect other processes but are not the direct controlling factor here.

Rising global temperature can increase the likelihood or intensity of several extreme events, including heat waves, intense rainfall, droughts, and some severe storms. It also contributes to sea-level rise and ecosystem disruption. New continents and changes in Earth’s gravity are not direct consequences of atmospheric warming, and seawater does not simply become fresh.

Reducing household electricity use can lower emissions when electricity is generated by burning coal, oil, or gas. Simple actions include switching off unused appliances, using efficient lighting, improving insulation, and choosing renewable electricity where available. The other options waste energy or use fuel unnecessarily, increasing household-related carbon emissions.

Forests remove carbon dioxide from the atmosphere through photosynthesis and store carbon in trunks, roots, leaves, litter, and soils. They are therefore important terrestrial carbon sinks. Oceans also absorb a large amount of carbon dioxide, but among the given choices, forests are the expected natural land-based system. Their carbon-storage capacity can decline when forests are cleared or burned.

Reducing dependence on coal, oil, and natural gas lowers emissions of carbon dioxide and other greenhouse gases. Replacing fossil fuels with renewable energy, improving efficiency, and reducing waste can therefore limit human-caused warming. More coal burning, open burning of residues, and deforestation increase emissions or reduce carbon uptake, so they worsen the problem.

The natural greenhouse effect is essential because gases in the atmosphere retain part of Earth’s outgoing heat and keep the average surface temperature suitable for liquid water and life. Without it, Earth would be much colder and less habitable. The harmful issue is the enhanced greenhouse effect caused by increasing human emissions, not the natural effect itself.

Carbon dioxide is a greenhouse gas because its molecules absorb infrared radiation emitted by Earth’s surface and re-emit part of that energy, helping retain heat in the atmosphere. It is not an inert gas category like helium or neon, and “alkaline gas” and “metallic gas” are not appropriate classifications for carbon dioxide in this context.

Trees absorb carbon dioxide during photosynthesis and store carbon in their biomass and surrounding soils. Protecting existing forests prevents this stored carbon from being released through deforestation and fire, while continued forest growth can remove additional CO2. Burning coal, open waste burning, and increased private-vehicle use generally add greenhouse-gas emissions.

Excessive heat can harm human health by causing dehydration, heat exhaustion, heatstroke, worsening of heart and lung diseases, and reduced ability to work safely. Children, older adults, people with illnesses, and outdoor workers are particularly vulnerable. The other options are not standard direct biological impacts of heat waves, so human health is the clear answer.

Persistently increasing greenhouse-gas emissions can produce a long-term climate impact because carbon dioxide and other gases remain in the atmosphere for varying periods and alter Earth’s energy balance. Continued warming can influence temperature, rainfall, sea level, ecosystems, and extreme events. A single day of rain or an isolated local event does not create global climate change.

Using less petrol, diesel, coal, or other fossil fuel reduces the amount of carbon dioxide released during combustion. Lower greenhouse-gas emissions reduce the extra heat retained in the atmosphere and therefore help slow global warming. Driving more, burning waste, and cutting trees generally increase emissions or reduce carbon absorption.

Methane is a major greenhouse gas because its molecules absorb outgoing infrared radiation and help retain heat in the atmosphere. Important human-related sources include livestock digestion, rice cultivation, landfills, and fossil-fuel extraction. Oxygen, nitrogen, and helium are abundant or inert atmospheric gases but are not significant greenhouse gases under ordinary conditions.