Observed and simulated full-depth ocean heat-content changes for 1970–2005

Lijing Cheng,Kevin E Trenberth,Matthew D Palmer,Jiang Zhu,John P Abraham

doi:10.5194/os-12-925-2016

Abstract

Abstract. Greenhouse-gas emissions have created a planetary energy imbalance that is primarily manifested by increasing ocean heat content (OHC). Updated observational estimates of full-depth OHC change since 1970 are presented that account for recent advancements in reducing observation errors and biases. The full-depth OHC has increased by 0.74 [0.68, 0.80] × 1022 J yr−1 (0.46 Wm−2) and 1.22 [1.16–1.29] × 1022 J yr−1 (0.75 Wm−2) for 1970–2005 and 1992–2005, respectively, with a 5 to 95 % confidence interval of the median. The CMIP5 models show large spread in OHC changes, suggesting that some models are not state-of-the-art and require further improvements. However, the ensemble median has excellent agreement with our observational estimate: 0.68 [0.54–0.82] × 1022 J yr−1 (0.42 Wm−2) from 1970 to 2005 and 1.25 [1.10–1.41] × 1022 J yr−1 (0.77 Wm−2) from 1992 to 2005. These results increase confidence in both the observational and model estimates to quantify and study changes in Earth's energy imbalance over the historical period. We suggest that OHC be a fundamental metric for climate model validation and evaluation, especially for forced changes (decadal timescales).

Highlights

Since the beginning of the industrial revolution, increased emissions of long-lived greenhouse gases such as carbon dioxide have resulted in an accumulation of thermal energy in the climate system (Trenberth et al, 2014; von Schuckmann et al, 2016) via the associated net energy imbalance at Earth’s top-of-atmosphere (TOA)
We show that the difference of this lower and upper bound of the 700 m–bottom ocean heat content (OHC) change is equal to ∼ 13 % (∼ 10 %) of the full-depth OHC change during 1970–1991 (1970–2005), which indicates the maximum error induced www.ocean-sci.net/12/925/2016/
This study presents new estimates of observed OHC change since 1970 based on improved mapping methods and XBT bias corrections

Summary

Introduction

Since the beginning of the industrial revolution, increased emissions of long-lived greenhouse gases such as carbon dioxide have resulted in an accumulation of thermal energy in the climate system (Trenberth et al, 2014; von Schuckmann et al, 2016) via the associated net energy imbalance at Earth’s top-of-atmosphere (TOA). Numerous efforts have been made to detect the historical OHC change (for example, Levitus et al, 2005; Gouretski and Koltermann, 2007; Smith and Murphy, 2007; Domingues et al, 2008; Palmer and Haines, 2009; Ishii and Kimoto, 2009; Lyman et al, 2010; Levitus et al, 2012; Balmaseda et al, 2013; Cheng et al, 2015a) and attribute causes to its variation (Palmer et al, 2009; Gleckler et al, 2012). A major source of error in the historical in situ temperature data that underpin OHC estimates are time-varying systematic biases in expendable bathythermograph (XBT) temperature measurements (Gouretski and Koltermann, 2007; Lyman et al, 2010; Abraham et al, 2013). Numerous correction schemes have been proposed to remove the time-varying XBT biases (Cheng et al, 2015b), but these schemes vary

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