Greenhouse effect and global warming

A carbon sink is a natural or human-managed system that absorbs more carbon dioxide or carbon than it releases over a given period. Forests store carbon in vegetation and soils, while oceans absorb carbon dioxide from the atmosphere. By removing and storing carbon, sinks reduce the amount available to strengthen the greenhouse effect.

Carbon dioxide and methane are greenhouse gases because their molecular structures allow them to absorb specific wavelengths of outgoing terrestrial infrared radiation and re-emit energy. This process helps retain heat in the lower atmosphere. They are not inert gases, and grouping them simply as major atmospheric gases is too broad to describe their shared climate property.

Albedo is the proportion or fraction of incoming solar radiation that a surface reflects back to space. Bright surfaces such as fresh snow and thick clouds generally have high albedo, while dark ocean water and forests have lower albedo and absorb more energy. It is therefore a measure of reflectivity, not pressure, rainfall, or salinity.

Many trees add a growth ring each year. The width, density, and sometimes chemical composition of these rings reflect growing conditions such as temperature, rainfall, moisture availability, and drought. By comparing rings from living and ancient wood, scientists reconstruct past climate variations. Thus, tree rings are indirect or proxy evidence, not direct measurements of tides or air colour.

Adaptation means adjusting human or natural systems so that they can cope with actual or expected climate impacts. Drought-resistant crops can maintain more reliable yields when rainfall is low or droughts last longer, so they help farmers adapt. Increasing coal production, deforestation, and open burning generally increase greenhouse-gas emissions and therefore worsen the causes of climate change rather than adapting to its effects.

Mitigation addresses the causes of climate change by reducing greenhouse-gas emissions or increasing carbon removal. Replacing coal and oil with low-carbon electricity from solar, wind, or other clean sources lowers carbon dioxide emissions from energy production. The other choices increase emissions or reduce carbon storage. This differs from adaptation, which prepares people and ecosystems to cope with impacts that are already occurring or expected.

Global warming refers to a sustained increase in Earth’s average surface temperature over long periods, commonly assessed using multi-decade climate records. A single hot day or a short heat wave describes weather, not the long-term climate trend. Long-term averages help scientists separate persistent warming from normal daily, seasonal, and year-to-year variability. The trend is linked mainly to increasing concentrations of human-produced greenhouse gases.

Adopting drought-tolerant crops is adaptation because it changes agricultural practice to reduce damage from a climate impact such as water scarcity or drought. Burning fossil fuels, open waste burning, and greater coal dependence increase greenhouse-gas emissions and are therefore harmful activities, not adaptation measures. Option A is uniquely correct.

Climate mitigation means reducing the causes of climate change, especially greenhouse-gas emissions or increasing carbon removal. Expanding solar and wind power can displace coal and gas, thereby lowering emissions from electricity generation. Coal expansion, deforestation, and open waste burning generally increase emissions, so only option A represents mitigation.

Carbon dioxide is one of the most important long-lived greenhouse gases after water vapour. It absorbs outgoing terrestrial infrared radiation and remains in the climate system long enough to influence global energy balance. Human activities, especially fossil-fuel combustion, cement production and land-use change, increase atmospheric carbon dioxide. Nitrogen, oxygen and helium are abundant or inert gases, but they do not significantly absorb the relevant infrared wavelengths.

Longwave radiation is mainly thermal infrared radiation emitted by Earth’s warmed surface, atmosphere and clouds. Because Earth is much cooler than the Sun, its outgoing radiation has longer wavelengths than incoming solar radiation. Greenhouse gases absorb and re-emit some of this longwave energy. Option B describes mainly shortwave solar radiation, while sea waves and dust transport are unrelated physical processes.

Albedo is the proportion of incoming solar radiation reflected by a surface. A high-albedo surface, such as fresh snow, ice or a bright cloud, reflects more energy back to space and absorbs less energy. It therefore generally warms less than a darker low-albedo surface under comparable conditions. High albedo does not automatically stop evaporation or determine air pressure, so options C and D are not necessary consequences.

Saving energy and avoiding unnecessary consumption reduce demand for electricity, transport fuel and manufactured products. When fossil fuels are burned less, emissions of carbon dioxide and other greenhouse gases decline. Coal use, deforestation and open burning have the opposite effect by increasing emissions and pollution. Thus option A is the valid individual mitigation measure.

Climate describes long-term patterns and averages rather than an isolated weather event. Records covering many decades reveal persistent trends in temperature, greenhouse-gas concentration, rainfall and other indicators. A single day’s sunshine, one river-width measurement or one cloud’s shape represents short-term conditions and cannot reliably establish long-term climate change.

Temperature controls crop development, flowering and maturity. Warming can shorten or lengthen these stages depending on the crop and region, while altered rainfall can affect sowing opportunities and irrigation needs. Consequently, farmers may need to change sowing and harvesting dates. The other choices are exaggerated or biologically impossible and are not general consequences of warming.

Energy efficiency and lower consumption reduce the amount of electricity, fuel and materials demanded by households. Where energy comes from fossil fuels, lower demand means fewer carbon dioxide emissions. Responsible consumption can also reduce industrial emissions and waste. Burning coal or plastic and cutting trees increase pollution or remove carbon sinks, so they cannot be suitable mitigation steps.

Energy efficiency provides the same service with less electricity or fuel, such as an efficient appliance producing the same cooling with lower power use. Lower energy demand reduces fuel extraction and combustion, especially where electricity comes from coal, oil or gas. This lowers greenhouse-gas emissions. It is not the same as directly removing CO2 from air or increasing rainfall.