Climate sensitivity

Equilibrium climate sensitivity50% increase in atmospheric CO2are net positiveclimate changeclimate feedback effectsdoubling of atmosphericdoubling of atmospheric CO 2 concentrations occurequilibrium and transient climate sensitivitymore sensitive to forcingssensitivity
Climate sensitivity is the globally averaged temperature change in response to changes in radiative forcing, which can occur, for instance, due to increased levels of carbon dioxide (CO2).wikipedia
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Global warming

climate changeglobal climate changeanthropogenic climate change
In the context of global warming, different measures of climate sensitivity are used. A committee on anthropogenic global warming, convened in 1979 by the United States National Academy of Sciences and chaired by Jule Charney, estimated climate sensitivity to be 3 °C-change, give or take 1.5 °C-change.
Climate model projections summarized in the report indicated that during the 21st century the global surface temperature is likely to rise a further 0.3 to 1.7 C-change in a moderate scenario, or as much as 2.6 to 4.8 C-change in an extreme scenario, depending on the rate of future greenhouse gas emissions and on climate feedback effects.

Climate change feedback

climate feedbackfeedbackfeedbacks
A component of climate sensitivity is directly due to radiative forcing, for instance by, and a further contribution arises from climate feedback, both positive and negative.
Climate change feedback is important in the understanding of global warming because feedback processes may amplify or diminish the effect of each climate forcing, and so play an important part in determining the climate sensitivity and future climate state.

Transient climate response to cumulative carbon emissions

linear relationship between global temperature rise and cumulative carbon dioxide emissions
A related concept is the transient climate response to cumulative carbon emissions, which is the globally averaged surface temperature change per unit of emitted.
As a measure of atmospheric carbon change, the TCRE parameterizes climate sensitivity and carbon sensitivity to formulate a value that is the temperature change (°C) per trillion tonnes of carbon emitted (Tt C).

Proxy (climate)

proxyproxiesclimate proxy
Climate sensitivity is typically estimated in three ways; by using observations taken during the industrial age, by using temperature and other data from the Earth's past and by modelling the climate system in computers.
A 2014 study was able to use the carbon-13 isotope ratios to estimate the CO 2 amounts of the past 400 million years, the findings hint at a higher climate sensitivity to CO 2 concentrations.

Cloud feedback

cloudsfeedback
The uncertainty is due entirely to feedbacks in the system: the water vapor feedback, the ice-albedo feedback, the cloud feedback, and the lapse rate feedback.
Differences in planetary boundary layer cloud modeling schemes can lead to large differences in derived values of climate sensitivity.

Radiative forcing

climate forcingSolar Forcingclimate forcing agents
Climate sensitivity is the globally averaged temperature change in response to changes in radiative forcing, which can occur, for instance, due to increased levels of carbon dioxide (CO2).

Tipping points in the climate system

tipping pointrunaway climate changetipping points
Furthermore, the climate may become more sensitive if tipping points are crossed.
The IPCC reports that feedbacks to increased temperatures are net positive for the remainder of this century, with the impact of cloud cover the largest uncertainty.

Climate inertia

climate change that they prevent is itself delayedinertialag
Due to climate inertia, the climate sensitivity depends upon the timescale.
The observed transient climate sensitivity and the equilibrium climate sensitivity are proportional to the thermal inertia time scale.

James Hansen

James E. HansenJim HansenDr. James Hansen
Apart from the Manabe and Wetherald model, with a climate sensitivity of 2 °C-change, the only other available was from James E. Hansen, with 4 °C-change.
They did note that the agreement between the observations and the intermediate scenario was accidental because the climate sensitivity used was higher than current estimates.

IPCC Fourth Assessment Report

Fourth Assessment ReportAR4Fourth
Authors of the IPCC Fourth Assessment Report stated that confidence in estimates of equilibrium climate sensitivity had increased substantially since the Third Annual Report.
Climate sensitivity is defined as the amount of global average surface warming following a doubling of carbon dioxide concentrations.

Jule Gregory Charney

Jule CharneyJule G. CharneyCharney
A committee on anthropogenic global warming, convened in 1979 by the United States National Academy of Sciences and chaired by Jule Charney, estimated climate sensitivity to be 3 °C-change, give or take 1.5 °C-change.
This estimate of climate sensitivity has been essentially unchanged for over three decades, e.g., the IPCC Fourth Assessment Report (2007) says that "equilibrium climate sensitivity is likely to be in the range 2°C to 4.5°C, with a best estimate value of about 3°C. It is very unlikely to be less than 1.5°C. Values substantially higher than 4.5°C cannot be excluded, but agreement with observations is not as good for those values."

Earth's energy budget

radiation budgetEarth Radiation BudgetEarth's radiation balance
The equilibrium climate sensitivity (ECS) is the temperature increase that would result from sustained doubling of the concentration of carbon dioxide in Earth's atmosphere, after the Earth's energy budget and the climate system reach radiative equilibrium.
Climate sensitivity is the steady state change in the equilibrium temperature as a result of changes in the energy budget.

Polar amplification

Arctic amplificationamplified response of the Arcticamplified in polar regions
Estimates of transient climate response (TCR) calculated from models and observational data can be reconciled if it is taken into account that fewer temperature measurements are taken in the polar regions, which warm more quickly than average.
The individual processes contributing to polar warming are critical to understanding climate sensitivity.

IPCC Third Assessment Report

Third Assessment ReportThirdTAR
The 2001 IPCC TAR also retained this likely range.
The TAR estimate for the climate sensitivity is 1.5 to 4.5 °C; and the average surface temperature is projected to increase by 1.4 to 5.8 Celsius degrees over the period 1990 to 2100, and the sea level is projected to rise by 0.1 to 0.9 metres over the same period.

Ice–albedo feedback

ice-albedo feedbackalbedo changesfeedback loop
The uncertainty is due entirely to feedbacks in the system: the water vapor feedback, the ice-albedo feedback, the cloud feedback, and the lapse rate feedback.

Economics of climate change mitigation

business-as-usualbaselinediscount rate
Because the economics of climate change mitigation depend a lot on how quickly carbon neutrality needs to be achieved, climate sensitivity is very important economically: one study suggests that halving the uncertainty of the transient climate response could save trillions of dollars.
These estimates depend on future emissions, climate sensitivity relative to increase in greenhouse gas concentrations, and the seriousness of impacts over time.

Paleocene–Eocene Thermal Maximum

Paleocene-Eocene Thermal MaximumPETMPaleocene-Eocene transition
The Paleocene–Eocene Thermal Maximum provides a good opportunity to study the climate system when it is in a warm state.

Carbon dioxide

CO 2 CO2carbon dioxide (CO 2 )
Climate sensitivity is the globally averaged temperature change in response to changes in radiative forcing, which can occur, for instance, due to increased levels of carbon dioxide (CO2).

Celsius

°CCdegrees Celsius
When climate sensitivity is expressed for a doubling of CO 2, its units are degrees Celsius (°C).

Carbon dioxide in Earth's atmosphere

carbon dioxide emissionsatmospheric carbon dioxideCO2 emissions
The equilibrium climate sensitivity (ECS) is the temperature increase that would result from sustained doubling of the concentration of carbon dioxide in Earth's atmosphere, after the Earth's energy budget and the climate system reach radiative equilibrium.

Climate system

The equilibrium climate sensitivity (ECS) is the temperature increase that would result from sustained doubling of the concentration of carbon dioxide in Earth's atmosphere, after the Earth's energy budget and the climate system reach radiative equilibrium.

Radiative equilibrium

equilibriumradiative
The equilibrium climate sensitivity (ECS) is the temperature increase that would result from sustained doubling of the concentration of carbon dioxide in Earth's atmosphere, after the Earth's energy budget and the climate system reach radiative equilibrium.

Anthropocene

anthropogenicThe AnthropoceneAnthropocene Extinction
Climate sensitivity is typically estimated in three ways; by using observations taken during the industrial age, by using temperature and other data from the Earth's past and by modelling the climate system in computers.

Computer simulation

computer modelsimulationcomputer modeling
Climate sensitivity is typically estimated in three ways; by using observations taken during the industrial age, by using temperature and other data from the Earth's past and by modelling the climate system in computers.

General circulation model

global climate modelglobal climate modelsclimate model
For coupled atmosphere-ocean global climate models the climate sensitivity is an emergent property; rather than being a model parameter it is a result of a combination of model physics and parameters.