Sensibilidad climática
A medida que se obliga a integraciones más cortas, es una sensibilidad transitoria del clima, que se define como la respuesta de la temperatura promedio durante un período de veinte años centrado en CO2 duplicando en una simulación transitoria con CO2 aumentando en un 1% por año.
[3][4] A pesar de la sensibilidad climática, se utiliza generalmente en el contexto del forzamiento radiativo por CO2, que se considera como una propiedad general del sistema climático: el cambio en la temperatura del aire (ΔTs) después de un cambio en las unidades en el forzante radiativo (FR) y se expresa en unidades de °C/(W/m²).
También es posible estimar la sensibilidad del clima, a partir de observaciones, sin embargo, esto es difícil debido a las incertidumbres en las historias del forzante y de la temperatura.
[8] En 2001, el IPCC adoptó el valor revisado de 3,7 W/m², y la diferencia se atribuye al "ajuste de la temperatura estratosférica"[9] More recently an intercomparison of radiative transfer codes (Collins et al., 2006)[10] showed substantial discrepancies among climate models and between climate models and more exact radiation codes in the forcing attributed to doubled CO2 even in cloud-free sky; presumably the differences would be even greater if forcing were evaluated in the presence of clouds because of differences in the treatment of clouds in different models.
Undoubtedly the difference in forcing attributed to doubled CO2 in different climate models contributes to differences in apparent sensitivities of the models, although this effect is thought to be small relative to the intrinsic differences in sensitivities of the models themselves (Webb et al., 2006) (enlace roto disponible en Internet Archive; véase el historial, la primera versión y la última).. Rahmstorf (2008)[5] provides an informal example of how climate sensitivity might be estimated empirically, from which the following is modified.
the equilibrium increase in global mean temperature including the effects of feedbacks due to a sustained forcing by doubled CO2 (taken as 3.7 W/m²), as x °C.
If Earth were to experience an equilibrium temperature change of ΔT (°C) due to a sustained forcing of ΔF (W/m²), then one might say that x/(ΔT) = (3.7 W/m²)/(ΔF), i.e.
Taking planetary heat uptake rate as the rate of ocean heat uptake, estimado por el Cuarto Informe de Evaluación del IPCC (IPCC AR4) as 0.2 W/m², yields a value for x of 2,1 °C (All numbers are approximate and quite uncertain.)
"... examine the change in temperature and solar forcing between glaciación (Edad de hielo) e interglacial (no ice age) periods.
[12] La estimación estándar de la sensibilidad del clima – 3 °C, más o menos 1,5 °C – tiene su origen en un comité sobre el calentamiento global antropogénico, convocado en 1979 por la National Academy of Sciences and chaired by Jule Charney.
"According to Manabe, Charney chose 0.5 °C as a not-unreasonable margin of error, subtracted it from Manabe’s number, and added it to Hansen’s.
Since then, many vastly improved models have been developed by a number of climate research centers around the world.
Current state-of-the-art climate models span a range of 2.6–4.1 °C, most clustering around 3 °C.
Andronova and Schlesinger (2001) found that the climate sensitivity could lie between 1 and 10 °C, with a 54 percent likelihood that it lies outside the IPCC range.
Annan and Hargreaves (2006)[22] presented an estimate that resulted from combining prior estimates based on analyses of paleoclimate, responses to volcanic eruptions, and the temperature change in response to forcings over the twentieth century.
Forster and Gregory (2006)[23] presented a new independent estimate based on the slope of a plot of calculated greenhouse gas forcing minus top-of-atmosphere energy imbalance, as measured by satellite borne radiometers, versus global mean surface temperature.
