Issues in Establishing Climate Sensitivity in Recent Studies

Numerous attempts have been made to constrain climate sensitivity with observations [1-10] (with [6] as LC09, [8] as SB11). While all of these attempts contain various caveats and sources of uncertainty, some efforts have been shown to contain major errors and are demonstrably incorrect. For example, multiple studies [11-13] separately addressed weaknesses in LC09 [6]. The work of Trenberth et al. [13], for instance, demonstrated a basic lack of robustness in the LC09 method that fundamentally undermined their results. Minor changes in that study's subjective assumptions yielded major changes in its main conclusions. Moreover, Trenberth et al. [13] criticized the interpretation of El Niño-Southern Oscillation (ENSO) as an analogue for exploring the forced response of the climate system. In addition, as many cloud variations on monthly time scales result from internal atmospheric variability, such as the Madden-Julian Oscillation, cloud variability is not a deterministic response to surface temperatures. Nevertheless, many of the problems in LC09 [6] have been perpetuated, and Dessler [10] has pointed out similar issues with two more recent such attempts [7,8]. Here we briefly summarize more generally some of the pitfalls and issues involved in developing observational constraints on climate feedbacks. The record of Earth's radiation budget from satellite measurements is short and discontinuous, and parts of it have problems [14,15] which complicate its use in climate sensitivity studies. The earlier Earth Radiation Budget Experiment (ERBE) era from about 1985 to 1989 used instrumentation and methods that have been improved in the Clouds and the Earth's Radiant Energy System (CERES) era after 2000 [16]. Accordingly, only a decade of accurate values is presently available with adequate stability to address the forced component of climate change. The estimated energy imbalance at the top-of-atmosphere (TOA) is estimated presently to be of order 1 W m −2 [17].