Sensitivity of Global Upper-Ocean Heat Content Estimates to Mapping Methods, XBT Bias Corrections, and Baseline Climatologies

Tim Boyer NOAA/National Centers for Environmental Information, Silver Spring, Maryland

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Catia M. Domingues Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
Antarctic Climate and Ecosystems Cooperative Research Institute, Hobart, Tasmania, Australia
Centre of Excellence for Climate System Science, Australian Research Council, Hobart, Tasmania, Australia

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Simon A. Good Met Office, Exeter, United Kingdom

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Gregory C. Johnson NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington

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John M. Lyman NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington
Joint Institute for Marine and Atmospheric Research, University of Hawai‘i at Mānoa, Honolulu, Hawaii

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Masayoshi Ishii Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan

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Viktor Gouretski Center for Earth System Research and Sustainability, CliSAP, Integrated Climate Data Center, University of Hamburg, Hamburg, Germany

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Josh K. Willis Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

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John Antonov University Corporation for Atmospheric Research, Boulder, Colorado

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Susan Wijffels Commonwealth Scientific and Industrial Research Organization, Hobart, Tasmania, Australia

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John A. Church Commonwealth Scientific and Industrial Research Organization, Hobart, Tasmania, Australia

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Rebecca Cowley Commonwealth Scientific and Industrial Research Organization, Hobart, Tasmania, Australia

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Nathaniel L. Bindoff Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
Antarctic Climate and Ecosystems Cooperative Research Institute, Hobart, Tasmania, Australia
Centre of Excellence for Climate System Science, Australian Research Council, Hobart, Tasmania, Australia
Commonwealth Scientific and Industrial Research Organization, Hobart, Tasmania, Australia

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Abstract

Ocean warming accounts for the majority of the earth’s recent energy imbalance. Historic ocean heat content (OHC) changes are important for understanding changing climate. Calculations of OHC anomalies (OHCA) from in situ measurements provide estimates of these changes. Uncertainties in OHCA estimates arise from calculating global fields from temporally and spatially irregular data (mapping method), instrument bias corrections, and the definitions of a baseline climatology from which anomalies are calculated. To investigate sensitivity of OHCA estimates for the upper 700 m to these different factors, the same quality-controlled dataset is used by seven groups and comparisons are made. Two time periods (1970–2008 and 1993–2008) are examined. Uncertainty due to the mapping method is 16.5 ZJ for 1970–2008 and 17.1 ZJ for 1993–2008 (1 ZJ = 1 × 1021 J). Uncertainty due to instrument bias correction varied from 8.0 to 17.9 ZJ for 1970–2008 and from 10.9 to 22.4 ZJ for 1993–2008, depending on mapping method. Uncertainty due to baseline mean varied from 3.5 to 14.5 ZJ for 1970–2008 and from 2.7 to 9.8 ZJ for 1993–2008, depending on mapping method and offsets. On average mapping method is the largest source of uncertainty. The linear trend varied from 1.3 to 5.0 ZJ yr−1 (0.08–0.31 W m−2) for 1970–2008 and from 1.5 to 9.4 ZJ yr−1 (0.09–0.58 W m−2) for 1993–2008, depending on method, instrument bias correction, and baseline mean. Despite these complications, a statistically robust upper-ocean warming was found in all cases for the full time period.

Pacific Marine Environmental Laboratory Contribution Number 4261 and Joint Institute for Marine and Atmospheric Research Contribution Number 16-393.

Corresponding author address: Tim Boyer, Ocean Climate Laboratory, National Centers for Environmental Information, 1315 East-West Highway, Silver Spring, MD 20910. E-mail: tim.boyer@noaa.gov

Abstract

Ocean warming accounts for the majority of the earth’s recent energy imbalance. Historic ocean heat content (OHC) changes are important for understanding changing climate. Calculations of OHC anomalies (OHCA) from in situ measurements provide estimates of these changes. Uncertainties in OHCA estimates arise from calculating global fields from temporally and spatially irregular data (mapping method), instrument bias corrections, and the definitions of a baseline climatology from which anomalies are calculated. To investigate sensitivity of OHCA estimates for the upper 700 m to these different factors, the same quality-controlled dataset is used by seven groups and comparisons are made. Two time periods (1970–2008 and 1993–2008) are examined. Uncertainty due to the mapping method is 16.5 ZJ for 1970–2008 and 17.1 ZJ for 1993–2008 (1 ZJ = 1 × 1021 J). Uncertainty due to instrument bias correction varied from 8.0 to 17.9 ZJ for 1970–2008 and from 10.9 to 22.4 ZJ for 1993–2008, depending on mapping method. Uncertainty due to baseline mean varied from 3.5 to 14.5 ZJ for 1970–2008 and from 2.7 to 9.8 ZJ for 1993–2008, depending on mapping method and offsets. On average mapping method is the largest source of uncertainty. The linear trend varied from 1.3 to 5.0 ZJ yr−1 (0.08–0.31 W m−2) for 1970–2008 and from 1.5 to 9.4 ZJ yr−1 (0.09–0.58 W m−2) for 1993–2008, depending on method, instrument bias correction, and baseline mean. Despite these complications, a statistically robust upper-ocean warming was found in all cases for the full time period.

Pacific Marine Environmental Laboratory Contribution Number 4261 and Joint Institute for Marine and Atmospheric Research Contribution Number 16-393.

Corresponding author address: Tim Boyer, Ocean Climate Laboratory, National Centers for Environmental Information, 1315 East-West Highway, Silver Spring, MD 20910. E-mail: tim.boyer@noaa.gov
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