Radiative forcing

[6] Carbon dioxide has the biggest impact on total forcing, while methane and chlorofluorocarbons (CFCs) play smaller roles as time goes on.

This happens continuously as sunlight hits the surface of Earth, clouds and aerosols form, the concentrations of atmospheric gases vary and seasons alter the groundcover.

Conversely, negative radiative forcing means that Earth loses more energy to space than it receives from the Sun, which produces cooling (global dimming).

RCE models began to account for more complex material flows within the energy balance, such as those from a water cycle, and thereby described observations better.

The RCE work distilled this into a forcing-feedback framework for change, and produced climate sensitivity results agreeing with those from GCMs.

This conceptual framework asserts that a homogeneous disturbance (effectively imposed onto the top-of-atmosphere energy balance) will be met by slower responses (correlated more or less with changes in a planet's surface temperature) to bring the system to a new equilibrium state.

ERF means that climate change drivers can be placed onto a more level playing field to enable comparison of their effects and a more consistent view of how global surface temperature responds to various types of human forcing.

[14] Radiative forcing and climate feedbacks can be used together to estimate a subsequent change in steady-state (often denoted "equilibrium") surface temperature (ΔTs) via the equation: where

[14] Earth's global radiation balance fluctuates as the planet rotates and orbits the Sun, and as global-scale thermal anomalies arise and dissipate within the terrestrial, oceanic and atmospheric systems (e.g.

This data record captures both the natural fluctuations and human influences on IRF; including changes in greenhouse gases, aerosols, land surface, etc.

For a well-mixed greenhouse gas, radiative transfer codes that examine each spectral line for atmospheric conditions can be used to calculate the forcing ΔF as a function of a change in its concentration.

For the purpose of some studies (e.g. climate sensitivity), C0 is taken as the concentration prior to substantial anthropogenic changes and has a value of 278 ppm as estimated for the year 1750.

[33] Various mechanism behind the logarithmic scaling has been proposed but the spectrum distribution of the carbon dioxide seems to be essential,[34] particularly a broadening in the relevant 15-μm band coming from a Fermi resonance present in the molecule.

[35][36][37] Somewhat different formulae apply for other trace greenhouse gases such as methane and N2O (square-root dependence) or CFCs (linear), with coefficients that may be found for example in the IPCC reports.

[40] Thus over long time scales, water vapor behaves as a system feedback that amplifies the radiative forcing driven by the growth of carbon dioxide and other trace gases.

Multiple satellite-based instruments including ERB, ACRIM 1-3, VIRGO, and TIM[44][45] have continuously measured TSI with improving accuracy and precision since 1978.

[50] TSI variations associated with sunspots contribute a small but non-zero net forcing in the context of decadal climate changes.

[46] Some research suggests they may have partly influenced climate shifts during the Little Ice Age, along with concurrent changes in volcanic activity and deforestation.

The radiative and climate forcings arising from changes in the Sun's insolation are expected to continue to be minor, notwithstanding some as-of-yet undiscovered solar physics.

[52][58] A fraction of incident solar radiation is reflected by clouds and aerosols, oceans and landforms, snow and ice, vegetation, and other natural and man-made surface features.

Global patterns in cloud formation and circulation are highly complex, with couplings to ocean heat flows, and with jet streams assisting their rapid transport.

Seasonal variations in planetary albedo can be understood as a set of system feedbacks that occur largely in response to the yearly cycling of Earth's relative tilt direction.

For example, human acts of deforestion typically raise Earth's reflectivity while introducing water storage and irrigation to arid lands may lower it.

Likewise considering feedbacks, ice loss in arctic regions decreases albedo while expanding desertification at low to middle latitudes increases it.

[60] Along with the hemispherical equivalence, some researchers interpret the remarkably small interannual differences as evidence that planetary albedo may currently be constrained by the action of complex system feedbacks.

Nevertheless, historical evidence also suggests that infrequent events such as major volcanic eruptions can significantly perturb the planetary albedo for several years or longer.

[6] The table includes the direct forcing contributions from carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O); chlorofluorocarbons (CFCs) 12 and 11;[failed verification] and fifteen other halogenated gases.

It might be observed that the total forcing for year 2016, 3.027 W m−2, together with the commonly accepted value of climate sensitivity parameter λ, 0.8 K /(W m−2), results in an increase in global temperature of 2.4 K, much greater than the observed increase, about 1.2 K.[67][failed verification] Part of this difference is due to lag in the global temperature achieving steady state with the forcing.

This index is a measure of the inter-annual changes in conditions that affect carbon dioxide emission and uptake, methane and nitrous oxide sources and sinks, the decline in the atmospheric abundance of ozone-depleting chemicals related to the Montreal Protocol.

An alternative table prepared for use in climate model intercomparisons conducted under the auspices of IPCC and including all forcings, not just those of greenhouse gases.