Climate Sensitivity - Improving Estimates

Cloud aggregation and climate models
New modeling casts doubt on the suitability of running experiments with fixed sea surface temperatures to understand the effects of cloud aggregation on Earth’s climate.

WolkenImPazifik_2019-03-17 16-43-58png
One of the fundamental metrics in climate change research is equilibrium climate sensitivity: the amount that Earth’s long-term, near-surface temperatures will change in response to a doubling of atmospheric carbon dioxide concentrations. Previous research has shown that two spatially dependent processes—the variability of sea surface temperatures and the organization of initially scattered convection (known as convective aggregation)—largely control climate sensitivity by regulating feedbacks related to clouds and water vapor that can amplify or moderate Earth’s ability to radiate heat into space.

Definition of climate sensitivity:

Climate sensitivity is the equilibrium temperature change in response to changes of the radiative forcing. ... The climate sensitivity specifically due to CO2 is often expressed as the temperature change in °C associated with a doubling of the concentration of carbon dioxide in Earth's atmosphere.

For coupled atmosphere-ocean global climate models (e.g. CMIP5) the climate sensitivity is an emergent property: it is not a model parameter, but rather a result of a combination of model physics and parameters. By contrast, simpler energy-balance models may have climate sensitivity as an explicit parameter.
Delta T_slambda cdot RF
The terms represented in the equation relate radiative forcing (RF) to linear changes in global surface temperature change (ΔTs) via the climate sensitivity λ.(

Radiative Forcing:

Radiative forcing or climate forcing is the difference between insolation (sunlight) absorbed by the Earth and energy radiated back to space.[1] The influences that cause changes to the Earth’s climate system altering Earth’s radiative equilibrium, forcing temperatures to rise or fall, are called climate forcings.[2] Positive radiative forcing means Earth receives more incoming energy from sunlight than it radiates to space. This net gain of energy will cause warming. Conversely, negative radiative forcing means that Earth loses more energy to space than it receives from the sun, which produces cooling.
Typically, radiative forcing is quantified at the tropopause or at the top of the atmosphere (often accounting for rapid adjustments in temperature) in units of watts per square meter of the Earth's surface. Positive forcing (incoming energy exceeding outgoing energy) warms the system, while negative forcing (outgoing energy exceeding incoming energy) cools it. Causes of radiative forcing include changes in insolation and the concentrations of radiatively active gases, commonly known as greenhouse gases, and aerosols.