Greenhouse effect and global warming

Global warming raises the long-term average temperature of the Earth system and can increase the likelihood, duration, or intensity of extreme heat events in many regions. Heat waves can harm human health, reduce agricultural productivity, increase water demand, and raise wildfire risk. The other choices describe impossible or unrelated changes. Thus, an increasing frequency of heat waves is a scientifically reasonable effect, making option A correct.

A carbon footprint is an estimate of the total greenhouse-gas emissions associated directly or indirectly with a person, product, organisation, or activity. It commonly includes carbon dioxide and other gases converted into carbon-dioxide equivalents. Therefore, option A gives the correct meaning.

Using public transport can reduce fuel consumption and the emissions produced per passenger, especially when it replaces many separate private-vehicle journeys. The exact benefit depends on the vehicle and occupancy, but it is generally a lower-emission choice than individual car travel. Hence, option A is correct.

Earth’s energy balance depends on a balance between incoming solar radiation and outgoing terrestrial radiation. If greenhouse-gas concentrations rise, more outgoing infrared energy is absorbed and re-emitted, so the system temporarily retains extra heat and warms until a new balance develops. Option A is correct.

Higher air and surface temperatures can increase melting at the surface and, in some cases, reduce snowfall that replenishes glacier ice. Over time, many glaciers may lose mass, retreat uphill, and shrink. This can first increase meltwater and later reduce water supply for rivers dependent on seasonal ice melt. The other options violate basic physical and geographical understanding. Therefore, option A is correct.

Climate-change adaptation means adjusting people, ecosystems, infrastructure, and institutions to actual or expected climate effects in order to reduce harm or take advantage of possible benefits. Examples include building flood-resistant infrastructure, using drought-tolerant crops, improving heat-warning systems, and managing water more carefully. Adaptation differs from mitigation, which addresses the causes of warming by reducing greenhouse-gas emissions. Hence, option A is correct.

Climate-change mitigation means reducing the sources of greenhouse gases or increasing their removal from the atmosphere. It includes improving energy efficiency, replacing fossil fuels with renewable energy, protecting and restoring forests, using low-carbon transport, and reducing methane emissions. Mitigation addresses the causes of climate change, whereas adaptation reduces damage from its effects. Therefore, the emission-reduction effort described in option A is correct.

Carbon dioxide, methane, and nitrous oxide absorb outgoing infrared radiation and are recognised greenhouse gases. Nitrogen is abundant in the atmosphere, but its molecule does not significantly absorb terrestrial infrared radiation under ordinary atmospheric conditions. Therefore, nitrogen is the correct answer to the ‘not’ question: option C.

In global warming, the word “global” refers to the Earth as a whole, especially the long-term rise in the planet’s average near-surface temperature. It does not mean that every place warms equally or that every day is hotter. Local temperatures can vary, but the global average is calculated across regions and over time. Thus, the phrase concerns the whole Earth, making option A correct.

The Sun is much hotter than Earth, so it emits most of its energy at relatively short wavelengths, including visible light and ultraviolet radiation. Earth receives this incoming shortwave solar radiation, reflects some of it, and absorbs the rest. After warming, Earth emits energy mainly as longwave terrestrial radiation. Therefore, the correct description of the energy received from the Sun is option A.

After absorbing part of the Sun’s incoming shortwave energy, Earth’s surface and atmosphere warm and emit energy outward as terrestrial longwave, or infrared, radiation. Because Earth is much cooler than the Sun, its outgoing radiation has longer wavelengths. Greenhouse gases absorb and re-emit some of this radiation, which is central to the greenhouse effect. Therefore, option A is correct.

The troposphere is the lowest layer of the atmosphere and contains most of the atmospheric mass and water vapour. Almost all weather occurs there, and greenhouse gases in this layer absorb and re-emit outgoing infrared radiation, influencing near-surface temperature and climate. Greenhouse gases may exist higher in the atmosphere too, but the main climate-related warming effect discussed at school level concerns the troposphere. Thus, option A is correct.

Coal is a carbon-rich fossil fuel. Burning it in power stations releases substantial carbon dioxide, along with other pollutants; carbon dioxide can remain in the atmosphere for a long time and strengthen the greenhouse effect. Consequently, coal-based electricity can contribute to global warming. Option A is correct.

The biosphere includes all living organisms and the ecosystems in which they live. Climate change alters temperature, rainfall, seasons, sea level, and the frequency of extreme events, so the suitable habitats and geographic ranges of many plants and animals may shift. Some species may migrate, decline, or face greater extinction risk when they cannot adapt quickly enough. Therefore, changing habitats are a clear biosphere impact, making option A correct.

Agriculture depends strongly on temperature, rainfall, soil moisture, and the length of growing seasons. Climate change can shift planting dates, increase heat or drought stress, intensify floods and pests, and alter crop yields. Effects vary by crop and region, but option A is the valid general answer.

Switching off appliances that are not needed prevents unnecessary electricity consumption. If the electricity is generated by coal, oil, or gas, using less of it also reduces fuel burning, carbon dioxide emissions, and other pollution. This simple action is an example of energy conservation and can be combined with efficient appliances and renewable energy. The other choices waste energy, so option A is the only correct answer.

Oceans absorb a large amount of the excess heat added to the climate system. Global warming can therefore raise sea-surface and ocean temperatures, contributing to coral bleaching, changes in marine habitats, thermal expansion of seawater, and stress on ocean ecosystems. The scientifically supported answer is option A.

Afforestation means establishing trees on land that was not recently forested. Growing trees remove carbon dioxide from the atmosphere through photosynthesis and store carbon in their trunks, roots, leaves, soil, and associated vegetation. Forests also provide habitats and help regulate water and local climate. Afforestation cannot replace rapid emission cuts, and poorly planned plantations may harm biodiversity, but among the given choices it is clearly the beneficial measure. Thus, A is correct.

Water vapour is naturally present in the atmosphere and is the most abundant greenhouse gas. It absorbs outgoing infrared radiation and contributes to the natural greenhouse effect. Its amount is mainly controlled by temperature and the water cycle, although human warming can amplify it as a feedback. Option A is correct.

Increasing greenhouse gases absorb and re-emit a greater share of the infrared radiation that Earth would otherwise lose to space. This directly increases heat retention in the lower atmosphere and surface system. Other changes may follow, but the most immediate climatic mechanism is greater trapping of heat. Option A is correct.

Adaptation means adjusting systems, behaviour, or infrastructure to reduce harm from actual or expected climate impacts. An improved warning system gives people time to evacuate, protect property, and prepare for floods. The other options increase environmental pressure rather than reduce vulnerability. Therefore, option A is correct.

International cooperation is essential because greenhouse gases released in one country mix throughout the atmosphere and influence climate everywhere. No country can solve global warming alone. Countries must coordinate emission reduction, clean technology, finance, research, and adaptation measures. Therefore, option A correctly explains why this is a global rather than a local problem.

Global warming raises average temperatures and can make heat waves more frequent or intense. Human exposure to extreme heat may cause dehydration, heat exhaustion, heatstroke, and worsening of heart or respiratory conditions. Sea-level rise, glacier melting, and coastal flooding are important climate impacts, but they are not direct health effects in this question. Thus A is correct.

The enhanced greenhouse effect is mainly associated with a rise in heat-trapping gases such as carbon dioxide, methane, and nitrous oxide. Human activities including fossil-fuel burning, deforestation, industry, and some agricultural practices increase these gases. They absorb more outgoing infrared radiation, causing warming. Therefore, option A identifies the basic cause.

In the greenhouse effect, gases in the atmosphere absorb and re-emit part of the outgoing longwave radiation released by Earth’s surface. This slows the loss of heat to space and keeps the lower atmosphere and surface warmer. The natural process is necessary for life, although its human-driven enhancement causes additional warming. Hence A is correct.