Climate change feedback in the context of "Cloud forcing"

Greenhouse gases (GHGs) are the gases in an atmosphere that trap heat, raising the surface temperature of astronomical bodies such as Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.27 [0.2–0.4] °C per decade over 2015–2024. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 53.6±5.2 Gt CO2e yr−1 over the last decade (2014–2023), as well as reductions in the strength of aerosol cooling.

The five most abundant greenhouse gases in Earth's atmosphere, listed in decreasing order of average global mole fraction, are: water vapor, carbon dioxide, methane, nitrous oxide, ozone. Other greenhouse gases of concern include chlorofluorocarbons (CFCs and HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons, SF
₆, and NF
₃. Water vapor causes about half of the greenhouse effect, acting in response to other gases as a climate change feedback.

Earth's climate system is a complex system with five interacting components: the atmosphere (air), the hydrosphere (water), the cryosphere (ice and permafrost), the lithosphere (earth's upper rocky layer) and the biosphere (living things). Climate is the statistical characterization of the climate system. It represents the average weather, typically over a period of 30 years, and is determined by a combination of processes, such as ocean currents and wind patterns. Circulation in the atmosphere and oceans transports heat from the tropical regions to regions that receive less energy from the Sun. Solar radiation is the main driving force for this circulation. The water cycle also moves energy throughout the climate system. In addition, certain chemical elements are constantly moving between the components of the climate system. Two examples for these biochemical cycles are the carbon and nitrogen cycles.

The climate system can change due to internal variability and external forcings. These external forcings can be natural, such as variations in solar intensity and volcanic eruptions, or caused by humans. Accumulation of greenhouse gases in the atmosphere, mainly being emitted by people burning fossil fuels, is causing climate change. Human activity also releases cooling aerosols, but their net effect is far less than that of greenhouse gases. Changes can be amplified by feedback processes in the different climate system components.

Radiative forcing (or climate forcing) is a concept used to quantify a change to the balance of energy flowing through a planetary atmosphere. Various factors contribute to this change in energy balance, such as concentrations of greenhouse gases and aerosols, and changes in surface albedo and solar irradiance. In more technical terms, it is defined as "the change in the net, downward minus upward, radiative flux (expressed in W/m) due to a change in an external driver of climate change." These external drivers are distinguished from feedbacks and variability that are internal to the climate system, and that further influence the direction and magnitude of imbalance. Radiative forcing on Earth is meaningfully evaluated at the tropopause and at the top of the stratosphere. It is quantified in units of watts per square meter, and often summarized as an average over the total surface area of the globe.

A planet in radiative equilibrium with its parent star and the rest of space can be characterized by net zero radiative forcing and by a planetary equilibrium temperature.

Cirrus (cloud classification symbol: Ci) is a genus of high cloud made of ice crystals. Cirrus clouds typically appear delicate and wispy with white strands. In the Earth's atmosphere, cirrus are usually formed when warm, dry air rises, causing water vapor deposition onto mineral dust and metallic particles at high altitudes. Globally, they form anywhere between 4,000 and 20,000 meters (13,000 and 66,000 feet) above sea level, with the higher elevations usually in the tropics and the lower elevations in more polar regions.

Cirrus clouds can form from the tops of thunderstorms and tropical cyclones and sometimes predict the arrival of rain or storms. Although they are a sign that rain and maybe storms are on the way, cirrus themselves drop no more than falling streaks of ice crystals. These crystals dissipate, melt, and evaporate as they fall through warmer and drier air and never reach the ground. The word cirrus comes from the Latin prefix cirro-, meaning "tendril" or "curl". Cirrus clouds warm the earth, potentially contributing to climate change. A warming earth will likely produce more cirrus clouds, potentially resulting in a self-reinforcing loop.

The scientific community has been investigating the causes of current climate change for decades. After thousands of studies, the scientific consensus is that it is "unequivocal that human influence has warmed the atmosphere, ocean and land since pre-industrial times." This consensus is supported by around 200 scientific organizations worldwide. The scientific principle underlying current climate change is the greenhouse effect, which provides that greenhouse gases pass sunlight that heats the earth, but trap some of the resulting heat that radiates from the planet's surface. Large amounts of greenhouse gases such as carbon dioxide and methane have been released into the atmosphere through burning of fossil fuels since the industrial revolution. Indirect emissions from land use change, emissions of other greenhouse gases such as nitrous oxide, and increased concentrations of water vapor in the atmosphere, also contribute to climate change.

The warming from the greenhouse effect has a logarithmic relationship with the concentration of greenhouse gases. This means that every additional fraction of CO₂ and the other greenhouse gases in the atmosphere has a slightly smaller warming effect than the fractions before it as the total concentration increases. However, only around half of CO₂ emissions continually reside in the atmosphere in the first place, as the other half is quickly absorbed by carbon sinks in the land and oceans. Further, the warming per unit of greenhouse gases is also affected by feedbacks, such as the changes in water vapor concentrations or Earth's albedo (reflectivity).

Ice–albedo feedback is a climate change feedback, where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Because ice is very reflective, it reflects far more solar energy back to space than open water or any other land cover. It occurs on Earth, and can also occur on exoplanets.

Since higher latitudes have the coolest temperatures, they are the most likely to have perennial snow cover, widespread glaciers and ice caps - up to and including the potential to form ice sheets. However, if warming occurs, then higher temperatures would decrease ice-covered area, and expose more open water or land. The albedo decreases, and so more solar energy is absorbed, leading to more warming and greater loss of the reflective parts of the cryosphere. Inversely, cooler temperatures increase ice cover, which increases albedo and results in greater cooling, which makes further ice formation more likely.