Greenhouse effect and global warming

A carbon footprint is the total greenhouse-gas emission associated with a person, product, organization, service, or activity, including relevant direct and indirect emissions. It is commonly expressed as carbon-dioxide equivalent, which allows gases such as methane to be compared using their warming effect. Rainfall, height, and wind direction are unrelated measurements.

Carpooling allows several people with similar routes to share one vehicle. If it replaces separate car journeys, fewer vehicles travel, so fuel use, traffic congestion, and carbon-dioxide emissions per passenger can fall. It does not instantly cool the atmosphere; its climate benefit is gradual and results from reducing fuel combustion.

Forests absorb carbon dioxide through photosynthesis and store carbon in trunks, branches, leaves, roots, litter, and soil. When the ecosystem absorbs more carbon than it releases over a period, it functions as a carbon sink. A reservoir is any carbon store, whereas sink specifically describes net removal from the atmosphere.

Permafrost can contain frozen organic matter that has been decomposing slowly for thousands of years. When thawing occurs, microbes become active and may produce methane, while some carbon is released as carbon dioxide. Methane is a powerful greenhouse gas, so this positive feedback can amplify warming and further thawing.

Carbon dioxide is a greenhouse gas because it absorbs outgoing infrared radiation at particular wavelengths and re-emits energy, slowing the loss of heat from Earth to space. Its concentration rises mainly through fossil-fuel burning, cement production, and land-use change. Oxygen, nitrogen, and argon are not significant absorbers of terrestrial infrared radiation.

Excessive heat increases sweating and water loss. If fluids and salts are not replaced, dehydration can cause thirst, weakness, headache, dizziness, and reduced physical performance. Heat exhaustion and heat stroke are also serious outcomes, but option A is a direct and broadly applicable effect. Adequate water, shade, and cooling reduce risk.

Rising sea level raises the baseline from which tides and storm surges occur. Consequently, coastal settlements, low-lying islands, wetlands, and river deltas face a greater risk of flooding, erosion, and salt-water intrusion. Sea-level rise does not build mountains, reduce earthquakes, or directly shorten the length of a day.

Saving electricity lowers household energy demand. Where power generation uses coal, oil, or gas, reduced demand means less fuel is burned and fewer greenhouse gases are emitted. Practical steps include switching off unused appliances, using efficient lighting, improving insulation, and choosing renewable electricity. The other options increase emissions or pollution.

Greenhouse gases, including carbon dioxide, methane, and water vapour, absorb some outgoing long-wave radiation emitted by Earth and re-radiate energy within the atmosphere. Their concentration therefore influences the balance between incoming and outgoing energy. Mountains can affect local conditions, but option A best answers the question about atmospheric heat balance.

Global warming causes thermal expansion of seawater and contributes to melting land ice, both of which raise sea level. Higher sea levels increase coastal flooding, erosion, salt-water intrusion, and storm-surge damage. Coastal populations and infrastructure are consequently more exposed. Mountain growth, fewer seeds, or stopped winds do not explain this climate-related risk, so A is correct.

Higher temperatures provide more energy for evaporation from oceans, lakes, rivers, vegetation, and soil. The resulting increase in atmospheric water vapour can alter cloud formation and the timing, intensity, and distribution of rainfall. It does not make rainfall equal everywhere or stop condensation. Therefore, the most direct answer is A.

Permafrost contains frozen remains of plants and animals. When it thaws, microorganisms decompose this organic matter; under oxygen-poor conditions, methane can be produced and released. Methane is a powerful greenhouse gas, so thawing permafrost can create a positive feedback that intensifies warming. Carbon dioxide may also be released, but methane is the expected answer here.

Trees and parks shade buildings and roads, while evapotranspiration uses heat to change water into vapour and cools the surrounding air. Increasing vegetation can therefore reduce the urban heat-island effect and improve thermal comfort. Concrete, dark roofs, traffic, and air-conditioner waste heat generally increase urban temperatures. Thus A is correct.

Global warming adds energy to the atmosphere and oceans and can intensify the water cycle. Depending on location, this can increase the likelihood or severity of heatwaves, intense rainfall, drought, and some storms. It does not mean every place will have permanent snow. The other options are physically unrelated, so extreme weather events, A, is correct.

Energy-efficient buildings use insulation, efficient lighting and appliances, passive design, and sometimes renewable energy to provide the same services with less purchased energy. Lower energy demand reduces fuel combustion in power plants and boilers, thereby lowering greenhouse-gas emissions and operating costs. Increased fossil-fuel use, pollution, and sea-level rise are not benefits. Therefore, A is correct.

Coastal regions can experience higher heat risk because warming combines with high humidity, reduced nighttime cooling, and occasional marine heatwaves. Humid air makes it harder for sweat to evaporate, increasing heat stress. Sea-level rise and stronger coastal hazards add vulnerability, although polar regions are also warming rapidly. In the intended comparison, coastal area is A.

Climate mitigation means addressing the causes of climate change by reducing greenhouse-gas emissions or increasing removals of gases such as carbon dioxide. Examples include renewable energy, energy efficiency, public transport, forest conservation, and carbon capture. Adjusting buildings, crops, or settlements to unavoidable impacts is adaptation, so option B—not A—is correct.

Greenhouse gases such as carbon dioxide, methane and water vapour absorb part of Earth’s outgoing infrared radiation and re-radiate it in the atmosphere. Changes in their concentration alter the balance between incoming solar energy and outgoing terrestrial heat, contributing to warming. The other options may have local effects but do not primarily explain this global heat-balance change.

Methane is strongly associated with livestock and some agricultural practices. Ruminant animals release methane during digestion, manure can produce it during decomposition, and flooded rice fields create oxygen-poor conditions where methane-forming microbes act. Nitrous oxide is also agricultural, especially through fertilisers, but methane is the expected livestock-linked answer.

Deforestation removes trees that absorb carbon dioxide through photosynthesis and store carbon in biomass and soils. It may also release stored carbon when vegetation is burned or decomposes. Consequently, atmospheric greenhouse gases can increase and the enhanced greenhouse effect can become stronger. Photosynthesis and biological CO2 absorption generally decline rather than increase.

The natural greenhouse effect allows gases such as water vapour, carbon dioxide and methane to retain part of Earth’s outgoing heat. This keeps the planet considerably warmer than it would otherwise be and helps maintain liquid water and conditions suitable for life. The enhanced greenhouse effect is harmful, but the natural effect itself is essential.

Concrete, asphalt and dense building materials absorb solar energy during the day and release it slowly after sunset. When vegetation is scarce, cities also lose shade and evaporative cooling. These conditions make urban areas warmer than nearby rural surroundings, intensifying the urban heat island effect. Snow cover and cold winds generally cool surfaces instead.

Permafrost contains frozen organic matter accumulated over long periods. When it thaws, microorganisms can decompose this material; in waterlogged, oxygen-poor conditions they may produce methane. Methane is a powerful greenhouse gas and can create a positive climate feedback by causing more warming. Carbon dioxide may also be released, but methane is the intended answer in this context.

Cement production releases carbon dioxide when limestone, mainly calcium carbonate, is heated and chemically decomposed into cement material. Industrial furnaces also often burn fossil fuels, adding further CO2 emissions. Methane can arise from other activities, but carbon dioxide is the principal gas directly associated with cement manufacture. Oxygen and nitrogen are not the correct emissions in this context.

A change in the concentration of greenhouse gases alters how much outgoing infrared radiation is absorbed and re-emitted by the atmosphere. Increasing carbon dioxide and methane generally strengthens heat retention and produces a positive energy imbalance that contributes to warming. Rivers, seeds and mountain height may influence local environments, but they are not the principal atmospheric greenhouse mechanism.