Changes in global net radiative imbalance 1985-2012.

Richard P Allan,Malcolm Roberts,Chunlei Liu,Pier‐Luigi Vidale,Doug Smith,Norman G Loeb,Matthew D Palmer

doi:10.1002/2014gl060962

Richard P Allan, Malcolm Roberts + Show 5 more

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https://doi.org/10.1002/2014gl060962

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Abstract

Combining satellite data, atmospheric reanalyses, and climate model simulations, variability in the net downward radiative flux imbalance at the top of Earth's atmosphere (N) is reconstructed and linked to recent climate change. Over the 1985–1999 period mean N (0.34 ± 0.67 Wm−2) is lower than for the 2000–2012 period (0.62 ± 0.43 Wm−2, uncertainties at 90% confidence level) despite the slower rate of surface temperature rise since 2000. While the precise magnitude of N remains uncertain, the reconstruction captures interannual variability which is dominated by the eruption of Mount Pinatubo in 1991 and the El Niño Southern Oscillation. Monthly deseasonalized interannual variability in N generated by an ensemble of nine climate model simulations using prescribed sea surface temperature and radiative forcings and from the satellite-based reconstruction is significantly correlated (r∼0.6) over the 1985–2012 period.

Highlights

The net imbalance (N) between absorbed shortwave radiation (ASR) and outgoing longwave radiation (OLR) at the top of Earth’s atmosphere is a fundamental climate variable; it represents a nexus between changes in radiative forcings and climate response but is influenced by unforced variability internal to the climate system [Hansen et al, 2011; Palmer et al, 2011; Otto et al, 2013]
Positive N indicates that energy is continuing to accumulate in the oceans, despite the apparent recent slower rates of global surface warming compared with the late twentieth century and with climate model simulations [Fyfe et al, 2013a; Watanabe et al, 2013]
ASR is calculated as the difference between incoming solar radiation from Solar Radiation and Climate Experiment and Clouds and the Earth’s Radiant Energy System (CERES) outgoing shortwave radiative flux; the OLR is adjusted such that N is consistent with observed ocean heat uptake measured by Argo data but making major assumptions about other minor energy sinks (N = 0.58 ± 0.43 W m−2 for July 2005 to June 2010 [Loeb et al, 2012])

Summary

Introduction

The net imbalance (N) between absorbed shortwave radiation (ASR) and outgoing longwave radiation (OLR) at the top of Earth’s atmosphere is a fundamental climate variable; it represents a nexus between changes in radiative forcings (which set the trajectory of climate change) and climate response (the magnitude of which is determined by feedbacks which may amplify or diminish climate responses) but is influenced by unforced variability internal to the climate system [Hansen et al, 2011; Palmer et al, 2011; Otto et al, 2013]. The slower recent observed rates of global surface warming have been attributed to a combination of factors as discussed by Trenberth and Fasullo [2013] These include cooling effects from natural radiative forcings [Solomon et al, 2011; Fyfe et al, 2013b; Kaufmann et al, 2011; Santer et al, 2014] and energy redistribution within the ocean due to unforced variability [Katsman and van Oldenborgh, 2011; Meehl et al, 2013; Kosaka and Xie, 2013; Watanabe et al, 2013; Balmaseda et al, 2013; England et al, 2014; Palmer and McNeall, 2014], important are sampling and measurement error of the surface temperature data [Kennedy, 2014; Cowtan and Way, 2013] and changes in stratospheric water vapor [Solomon et al, 2010; Garfinkel et al, 2013]; anthropogenic aerosol may play a minor role [Kaufmann et al, 2011; Murphy, 2013]. HadCRUT4 v4.1.1.0 CMIP5 modelsa CanESM2 CNRM-CM5 GISS-E2-R HadGEM2-ES INM-CM4 IPSL-CM5A-LR MIROC5 MRI-CGCM3 NorESM1-M

Data Sets

Methodology

Evaluating Changes in Radiative Fluxes

Findings

Discussion