Is the World Ocean Warming? Upper-Ocean Temperature Trends: 1950–2000

Harrison, D. E.; Carson, Mark

doi:10.1175/jpo3005.1

Cited by 56 publications

(42 citation statements)

References 16 publications

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“…It turns out that observed density shows increasing trends particularly in the western part of the tropical Pacific. This is consistent with observed temperature decreases in this region (Harrison and Carson, 2007). Hence density trends at 300 dbar differ between model and observations, but as they are primarily related to warming and with solubility changes contribution little to the total DO trends (Fig.…”

Section: Discussionsupporting

confidence: 86%

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

2012

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Abstract. Observations and model runs indicate trends in dissolved oxygen (DO) associated with current and ongoing global warming. However, a large-scale observation-tomodel comparison has been missing and is presented here. This study presents a first global compilation of DO measurements covering the last 50 yr. It shows declining upperocean DO levels in many regions, especially the tropical oceans, whereas areas with increasing trends are found in the subtropics and in some subpolar regions. For the Atlantic Ocean south of 20 • N, the DO history could even be extended back to about 70 yr, showing decreasing DO in the subtropical South Atlantic. The global mean DO trend between 50 • S and 50 • N at 300 dbar for the period 1960 to 2010 is −0.066 µmol kg −1 yr −1 . Results of a numerical biogeochemical Earth system model reveal that the magnitude of the observed change is consistent with CO 2 -induced climate change. However, the pattern correlation between simulated and observed patterns of past DO change is negative, indicating that the model does not correctly reproduce the processes responsible for observed regional oxygen changes in the past 50 yr. A negative pattern correlation is also obtained for model configurations with particularly low and particularly high diapycnal mixing, for a configuration that assumes a CO 2 -induced enhancement of the C : N ratios of exported organic matter and irrespective of whether climatological or realistic winds from reanalysis products are used to force the model. Depending on the model configuration the 300 dbar DO trend between 50 • S and 50 • N is −0.027 to −0.047 µmol kg −1 yr −1 for climatological wind forcing, with a much larger range of −0.083 to +0.027 µmol kg −1 yr −1 for different initializations of sensitivity runs with reanalysis wind forcing. Although numerical models reproduce the overall sign and, to some extent, magnitude of observed ocean deoxygenation, this degree of realism does not necessarily apply to simulated regional patterns and the representation of processes involved in their generation. Further analysis of the processes that can explain the discrepancies between observed and modeled DO trends is required to better understand the climate sensitivity of oceanic oxygen fields and predict potential DO changes in the future.

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Section: Discussionsupporting

confidence: 86%

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

2012

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“…and AchutaRao et al (2006) instead sampled models to mimic the Levitus et al (2001) calculation and found large discrepancies between global and hemispheric averages, including, in the former, sign reversals [somewhat in conflict with the results of Barnett et al (2001)]. Harrison and Carson (2007) discuss the great difficulties in inferring global upper ocean averages from the data after 1950 and call attention to the need for far better understanding of the accuracies of quoted subglobal averages.…”

Section: ) Lower Bounds On the Sampling Errorsmentioning

confidence: 88%

Decadal Trends in Sea Level Patterns: 1993–2004

2007

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Estimates of regional patterns of global sea level change are obtained from a 1°horizontal resolution general circulation model constrained by least squares to about 100 million ocean observations and many more meteorological estimates during the period 1993-2004. The data include not only altimetric variability, but most of the modern hydrography, Argo float profiles, sea surface temperature, and other observations. Spatial-mean trends in altimetric data are explicitly suppressed to isolate global average long-term changes required by the in situ data alone. On large scales, some regions display strong signals although few individual points have statistically significant trends. In the regional patterns, thermal, salinity, and mass redistribution contributions are all important, showing that regional sea level change is tied directly to the general circulation. Contributions below about 900 m are significant, but not dominant, and are expected to grow with time as the abyssal ocean shifts. Estimates made here produce a global mean of about 1.6 mm yr Ϫ1, or about 60% of the pure altimetric estimate, of which about 70% is from the addition of freshwater. Interannual global variations may be dominated by the freshwater changes rather than by heating changes. The widely quoted altimetric global average values may well be correct, but the accuracies being inferred in the literature are not testable by existing in situ observations. Useful estimation of the global averages is extremely difficult given the realities of space-time sampling and model approximations. Systematic errors are likely to dominate most estimates of global average change: published values and error bars should be used very cautiously.

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“…A number of recent studies (e.g., Harrison and Carson 2007;Cravatte et al 2009) describe limitations imposed by poor historical data records in temperature and salinity observations for the global and Pacific Oceans, respectively. However, these studies analyze the ocean in small spatial bins, increasing the chance of noise swamping a broad-scale trend signal.…”

Section: Significance Of Resolved Trendsmentioning

confidence: 99%

Fifty-Year Trends in Global Ocean Salinities and Their Relationship to Broad-Scale Warming

2010

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Using over 1.6 million profiles of salinity, potential temperature, and neutral density from historical archives and the international Argo Program, this study develops the three-dimensional field of multidecadal linear change for ocean-state properties. The period of analysis extends from 1950 to 2008, taking care to minimize the aliasing associated with the seasonal and major global El Niñ o-Southern Oscillation modes. Large, robust, and spatially coherent multidecadal linear trends in salinity to 2000-dbar depth are found. Salinity increases at the sea surface are found in evaporation-dominated regions and freshening in precipitationdominated regions, with the spatial pattern of change strongly resembling that of the mean salinity field, consistent with an amplification of the global hydrological cycle. Subsurface salinity changes on pressure surfaces are attributable to both isopycnal heave and real water-mass modification of the temperaturesalinity relationship. Subduction and circulation by the ocean's mean flow of surface salinity and temperature anomalies appear to account for most regional subsurface salinity changes on isopycnals. Broad-scale surface warming and the associated poleward migration of isopycnal outcrops drive a clear and repeating pattern of subsurface isopycnal salinity change in each independent ocean basin. Qualitatively, the observed global multidecadal salinity changes are thus consonant with both broad-scale surface warming and the amplification of the global hydrological cycle.

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Is the World Ocean Warming? Upper-Ocean Temperature Trends: 1950–2000

Cited by 56 publications

References 16 publications

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr

Decadal Trends in Sea Level Patterns: 1993–2004

Fifty-Year Trends in Global Ocean Salinities and Their Relationship to Broad-Scale Warming

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