Greenhouse effect and global warming

Albedo is the proportion of incoming solar radiation reflected by a surface. A higher albedo sends more sunlight back to space and leaves less energy available for absorption by the surface. This can produce a cooling influence, as seen with bright snow and ice. Greater absorption is associated with lower albedo, while high albedo does not automatically remove water vapour or create ozone.

The natural greenhouse effect is produced by naturally occurring gases such as water vapour, carbon dioxide and methane. It keeps Earth warm enough for liquid water and life. Human activities increase the concentration of several greenhouse gases, strengthening the natural effect and causing additional warming. Thus, the problem is not the existence of the natural effect but its anthropogenic enhancement.

Mitigation means addressing the causes of climate change, especially by reducing greenhouse-gas emissions or increasing removals. Solar, wind and other renewable sources can replace coal, oil and gas in electricity and other energy uses, lowering carbon dioxide emissions during operation. Adaptation, in contrast, means adjusting to climate impacts, so option B describes adaptation rather than mitigation.

Adaptation means adjusting practices, systems, or behaviour to reduce the harmful effects of actual or expected climate change. Using drought-tolerant seeds helps farmers maintain crop production when rainfall is low or irregular. Burning coal, cutting forests, and openly burning waste increase emissions and are not adaptation measures.

Climate justice is needed because countries have contributed unequally to greenhouse-gas emissions, while the effects of climate change are also distributed unequally. Many low-emitting communities are highly vulnerable to floods, droughts, heat, and sea-level rise. Justice therefore considers responsibility, capacity, vulnerability, and fairness.

A carbon budget is the maximum cumulative amount of carbon dioxide or greenhouse-gas emissions that can be released while keeping global warming below a chosen temperature limit with a specified probability. It is a limit, not a measuring instrument or physical geographical feature, and it guides emission-reduction planning.

The carbon budget represents the remaining cumulative emissions compatible with a chosen temperature goal. If it is used rapidly, less allowance remains for the future, increasing the chance that atmospheric greenhouse-gas concentrations and global warming will exceed the intended temperature limit. The other options are not consequences of exhausting a carbon budget.

Long-term warming is identified from a persistent rise in average temperatures across many years or decades, using observations from reliable stations, oceans, and other records. A single sunny day, dust event, or lightning episode describes short-term weather or a local event and cannot establish a climate trend by itself.

Concrete, asphalt, roofs, and other urban materials absorb and store solar energy, then release it slowly, especially after sunset. Cities also have less vegetation, so evaporative cooling is reduced. These factors make urban areas warmer than nearby rural locations. Wind need not stop completely, and ice or glacier growth is unrelated.

Greenhouse gases such as carbon dioxide, methane, and water vapour absorb some of Earth’s outgoing longwave infrared radiation. They re-emit energy in all directions, including toward the surface, which slows heat loss and warms the lower atmosphere. They do not alter Earth–Sun distance, remove the main atmospheric gases, or freeze seawater directly.

An enhanced greenhouse effect raises the average temperature of the lower atmosphere and changes the climate system. Over time it can increase the likelihood or intensity of some heat waves, heavy rainfall, droughts, wildfires, and other extremes, although the exact response differs by region and event. The other options are not expected consequences.

The natural greenhouse effect keeps Earth substantially warmer than it would otherwise be by absorbing and re-emitting outgoing infrared radiation. If most greenhouse gases disappeared, much more heat would escape to space, causing a severe fall in average surface temperature. This would disrupt liquid water and make present life conditions extremely difficult.

Climate describes long-term averages, variability, and patterns, usually assessed over decades or longer. Weather can change from hour to hour, day to day, or season to season, and one unusual event cannot establish a climate trend. A sufficiently long time scale helps separate persistent human-driven changes from short-term natural variability.

Albedo is the fraction of incoming solar radiation reflected by a surface. A high-albedo surface, such as fresh snow or ice, reflects more energy and absorbs less, so it generally remains cooler. A dark forest, ocean, or asphalt surface usually has lower albedo and absorbs more solar energy. Thus option B describes the opposite condition.

A climate trend requires analysis of observations over many years or decades. Long-term averages, anomalies, variability, and the direction of change help reveal whether temperature or rainfall is rising, falling, or remaining stable. One unusually warm year may result from natural variability, while annual maximums alone give an incomplete picture.

Emission limits control the amount of greenhouse gases released by energy, transport, industry, agriculture, and other activities. Limiting cumulative emissions slows the buildup of heat-trapping gases and improves the possibility of keeping global temperature rise within an agreed target. The policy is not intended to stop rainfall, remove clouds, or alter seawater colour.

The last ice age was a prolonged natural cold phase associated with extensive continental ice sheets and lower global temperatures. The current climate trend is a rapid warming phase, primarily driven by human activities that increase greenhouse-gas concentrations. Although natural climate changes have occurred before, the causes, rate, and present direction are different.

Energy efficiency provides the same service or output with less energy, such as lighting a room or producing goods with less electricity or fuel. Lower energy demand reduces the amount of coal, oil, and gas burned, thereby decreasing carbon dioxide and other greenhouse-gas emissions. It is therefore an important mitigation measure, although efficiency should accompany clean energy and conservation.

Increasing carbon dioxide strengthens the greenhouse effect by absorbing more outgoing terrestrial infrared radiation. Although both land and sea can warm, land generally responds faster because it has lower heat capacity and less vertical mixing. The ocean stores and redistributes heat more effectively, so it warms more slowly. Thus, the land-sea thermal contrast may increase, especially over seasonal or short-term periods. Option B reverses the heat-capacity relationship.

At night, Earth’s surface continues to emit thermal energy as longwave infrared radiation, even though solar shortwave radiation is absent. Greenhouse gases absorb part of this outgoing radiation and re-emit energy in all directions, including downward toward the surface. This reduces the net loss of heat from the surface to space and can make nights warmer. The effect does not mean that the surface stops radiating.

The natural greenhouse effect is produced when gases such as water vapour, carbon dioxide and methane absorb and re-emit outgoing infrared radiation, keeping Earth habitable. The enhanced greenhouse effect means that human activities add greenhouse gases or increase their concentration, disturbing the energy balance and producing additional warming. It does not mean that rainfall always stops or that Earth’s axis changes.

Earth receives mostly shortwave solar radiation, which warms the surface. The warmed surface then emits energy as longwave infrared radiation. Greenhouse gases such as carbon dioxide, methane and water vapour absorb some of this outgoing radiation and re-emit it, including downward toward Earth. This natural process warms the lower atmosphere and surface; increasing greenhouse gases strengthens it. Therefore, atmospheric absorption of longwave radiation is the physical basis.

Snow and ice have high albedo, so they reflect a large proportion of incoming solar energy. When warming melts them, darker ocean water or land is exposed. These surfaces have lower albedo and absorb more solar radiation, storing additional heat and causing further warming. This self-reinforcing sequence is called the ice-albedo positive feedback. The process is not caused by a cooler Sun, zero air pressure or increased nitrogen.

Nitrous oxide is a long-lived and powerful greenhouse gas. It absorbs outgoing infrared radiation and therefore increases radiative forcing and global warming. Important human sources include nitrogen fertiliser use, agricultural soils, manure management and some industrial processes. In addition, nitrous oxide contributes to stratospheric ozone destruction. Its main climate significance is not cloud formation, ocean drying or any change in Earth’s axis.

Combustion of coal, petroleum and natural gas converts stored carbon into carbon dioxide and also produces other gases and aerosols. The increased carbon dioxide concentration absorbs more outgoing infrared radiation, strengthening the greenhouse effect and disturbing Earth’s energy balance. The resulting warming can influence oceans, ice, rainfall and circulation patterns. Fossil-fuel burning does not create the stratospheric ozone layer or stop all rainfall.