CCN

Cloud condensation nuclei

CFC

Chlorofluorocarbon

Climate feedback

An amplification or dampening of the climate response to a specific forcing due to changes in the atmosphere, oceans, land, or continental glaciers.

Climate forcing

An energy imbalance imposed on the climate system either externally or by human activities.

Climate model

A simplified mathematical representation of the Earth’s climate system.

Climate response

Change in the climate system resulting from a climate forcing.

Climate sensitivity parameter or climate feedback parameter (λ)

The equilibrium global mean temperature change (°C) for a 1 W m⁻² TOA radiative forcing. λ is typically in the range of 0.3-1.4°C m² W⁻¹ in the current generation of GCMs. Climate sensitivity has played a central role in interpretation of model outputs, in evaluation of future climate changes expected from various scenarios, and it is closely linked to attribution of currently observed climate changes. An ongoing challenge to models and to climate projections has been to better define this key parameter and to understand the differences in computed values between various models.

Climate system

The system consisting of the atmosphere, hydrosphere, lithosphere, and biosphere, determining the Earth’s climate as the result of mutual interactions and responses to external influences (forcing). Physical, chemical, and biological processes are involved in interactions among the components of the climate system. (AMS)

Coupled Model

A class of analytical or numerical time-dependent models in which at least two different subsystems of Earth’s climate system are allowed to interact. These subsystems may include the atmosphere, hydrosphere, cryosphere, and biosphere. This term is most commonly used for models of the evolution and interaction of Earth’s atmosphere and ocean. Coupled (two-way) interaction between different subsystems can be contrasted with the class of models in which the evolution of subsystem A is affected by the present state of subsystem B, but changes in A do not feed back on the evolution of B itself. (AMS)

CMDL

Climate Monitoring and Diagnostics Laboratory

Cryosphere

That portion of the Earth where natural materials (water, soil, etc.) occur in frozen form. Generally limited to the polar latitudes and higher elevations. (AMS)