Abstract
The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. There are also numerous processes that introduce strong, regionalized variations to the overall warming trend. However, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. Here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. This can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. This must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response.
Highlights
The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases
We show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer
In this work we have demonstrated that it is the variations in the effective heat capacity of the atmosphere, defined by the planetary boundary layer (PBL) depth, which can explain these differences in climate forcing efficacy
Summary
The Earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. In addition to the detection of the influence of enhanced GHGs on surface temperatures, there have been numerous studies assessing how clouds[8–12], precipitation[8,12,13] and soil moisture[8,12] may have introduced some of the observed temporal and regional variations to the overall warming trend that has been seen in the latter half of the twentieth century. In all these studies, the authors have adopted the commonly accepted linear regression model for establishing the relationship between a change in a given property and the temperature response[14]. The hypothesis we put forward here presumes that there is essentially a decoupling of the planetary boundary layer (PBL)
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