Comments On “Human-induced Global Ocean Warming On Multidecadal Timescales” By Gleckler Et Al 2012

source of figure from Gleckler et al 2012

There is a new paper

P. J. Gleckler, B. D. Santer, C. M. Domingues, D. W. Pierce, T. P. Barnett, J. A. Church, K. E. Taylor, K. M. AchutaRao, T. P. Boyer, M. Ishii & P. M. Caldwell: 2012 Human-induced global ocean warming on multidecadal timescales. Nature Climate Change doi:10.1038/nclimate1553

which has been receiving media attention; e.g. see from the ABC Radio Australia

Research shows humans main cause of global warming.

Judy Curry has a post on June 12 2012 worth reading on this paper and other papers on this subject on her weblog in

Causes(?) of ocean warming

The news article contains the text [highlight added]

Scientists say this is the most comprehensive study to date on global ocean warming.

The research has been published in the journal Nature Climate Change.

The team looked at rising ocean temperatures over the past 50 years, and a dozen models projecting climate change patterns.

Australian based co-author, Dr John Church from Australia’s island state of Tasmania says there’s no way all of the world’s oceans could’ve warmed by one tenth of a degree Celsius without human impact.

He says nature only accounts for 10 per cent of the increase.

Dr Church says researchers from America, Australia, Japan and India examined a dozen different models used to project climate change, past studies have only looked at a couple at a time.

“And this has allowed the group to rule out that the changes are related to natural variability in the climate system,” he said.

Leading climate change and oceanography expert, Professor Nathan Bindoff says scientists are now certain man-made greenhouse gases are the primary cause.

“The evidence is unequivocal for global warming,” he said.

He says the new research balances the man-made impacts of warming greenhouse gases and cooling pollution in the troposphere, against natural changes in the ocean’s temperature and volcanic eruptions.

“This paper is  important because for the first time we can actually say that we’re virtually certain that the oceans have warmed, and that warming is caused not by natural processes but by rising greenhouse gases primarily,” he said

The Nature Climate Change article has the abstract

Large-scale increases in upper-ocean temperatures are evident in observational records. Several studies have used well-established detection and attribution methods to demonstrate that the observed basin-scale temperature changes are consistent with model responses to anthropogenic forcing and inconsistent with model-based estimates of natural variability. These studies relied on a single observational data set and employed results from only one or two models. Recent identification of systematic instrumental biases in expendable bathythermograph data has led to improved estimates of ocean temperature variability and trends and provide motivation to revisit earlier detection and attribution studies. We examine the causes of ocean warming using these improved observational estimates, together with results from a large multimodel archive of externally forced and unforced simulations. The time evolution of upper ocean temperature changes in the newer observational estimates is similar to that of the multimodel average of simulations that include the effects of volcanic eruptions. Our detection and attribution analysis systematically examines the sensitivity of results to a variety of model and data-processing choices. When global mean changes are included, we consistently obtain a positive identification (at the 1% significance level) of an anthropogenic fingerprint in observed upper-ocean temperature changes, thereby substantially strengthening existing detection and attribution evidence.

Their text includes the summary

“We have identified a human-induced fingerprint in observed estimates of upper-ocean warming on multidecadal timescales, confirming the results of previous D&A work2, 3, 4, 5. work. Our results are robust to the use of multiple bias-corrected observational data sets, to use of infilled or subsampled data, to model signal and noise uncertainties and to different technical choices in simulation drift removal and in the application of our D&A method. There is evidence from our variability comparisons that the models used here may underestimate observed decadal scale variability of basin-average upper-ocean temperatures. However, this variability underestimate would have to be smaller than observed by a factor of more than two to negate our positive identification of an anthropogenic fingerprint in the observed multidecadal warming of the upper 700 m of the oceans. Our analysis provides no evidence of a noise error of this magnitude.”

This post is to comment on several aspects of that paper:

1. The paper ended their analysis in 2008 [see figure at the top of this post].  While this may not have changed their trend analysis, it is an important issue in that, unlike a temperature at a single level where there is a lag between heat imposed and the temperature response, their temperatures are globally and 0-700m averaged values.  Since this layer contains the large majority of the heat changes in the climate system, any time lag it has with respect to an imposed heating or cooling would be small.  This mass weighted temperature can be directly converted to Joules as Levitus et al did in their paper, which I posted on, for example, in

Comment On Ocean Heat Content “World Ocean Heat Content And Thermosteric Sea Level Change (0-2000), 1955-2010″ By Levitus Et Al 2012

Levitus et al 2012 wrote for the period 1955-2010 that

The heat content of the world ocean for the 0-2000 m layer increased by 24.0×1022 J corresponding to a rate of 0.39 Wm-2 (per unit area of the world ocean) and a volume mean warming of 0.09ºC. This warming rate corresponds to a rate of 0.27 Wm-2 per unit area of earth’s surface. The heat content of the world ocean for the 0-700 m layer increased by 16.7×1022 J corresponding to a rate of 0.27 Wm-2 (per unit area of the world ocean) and a volume mean warming of 0.18ºC. The world ocean accounts for approximately 90% of the warming of the earth system that has occurred since 1955.

In my post, as a result of their finding, I concluded in my post that

Thus either using the 1955 to 2010 time period, or the shorter time period from 1990 to 2010 in the Levitus et al 2012 paper, the diagnosed magnitudes of ocean warming and global warming are significantly less than claimed by Jim Hansen in 2005. This discrepancy is even larger if we use the NOAA’s Pacific Marine Environmental Laboratory data.

Gleckler et al 2012 neglect to comment on the radiative imbalance diagnosed from the Levitus et al 2012 paper. Even though both were published in 2012, Glecker and colleagues certainly must have had an opportunity to update their paper with the Levitus et al 2012 new paper.

2.  The Glecker et al 2012 paper seems to ignore some non-CO2 positive human-caused radiative forcings. This includes black carbon, for example, in which in the paper

Jacobson, M. Z. (2010), Short‐term effects of controlling fossil‐fuel soot, biofuel soot and gases, and methane on climate, Arctic ice, and air pollution health, J. Geophys. Res., 115, D14209, doi:10.1029/2009JD013795

that I posted on in

Soot and Climate Change – A New Article By Jacobson 2010

Jacobson et al 2010 concluded that

fossil‐fuel soot, solid‐biofuel soot and gases, and CH4  may be the second leading cause of warming after CO2

and that eliminating them would

reduce global surface air temperatures by a statistically significant 0.3–0.5 K, 0.4–0.7 K, and 0.2–0.4 K, respectively, averaged over 15 years.

This conclusion conflicts with the statement in the news article by Nathan Bindoff that

man-made greenhouse gases are the primary cause

of the warming in the oceans. There still would be a discernible human influence, but it is more than just from greenhouse gases, as Nathan Bindoff claims.

The report

National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties.Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington,D.C., 208 pp.

adds to the uncertainty in terms of what we know about positive (and negative) radiative forcings from aerosols. See Table 2-2 in that report where, with respect to aerosol indirect effects on clouds,  the “semidirect effect” and the  glaciation indirect effect” have uncertain positive forcing and the “thermodynamic effect” is of unknown magnitude.

Clearly, our understanding of the relative contributions of different human radiatice forcings is still uncertain.

3. The Glecker et al article also still may underestimate natural variations in upper ocean content, as Judy Curry documents in her weblog post Causes(?) of ocean warming. This has also been documented in the Ph.d. dissertation by Marcia Wyatt, reported recently on in the post

Marcia Wyatt’s University of Colorado at Boulder Ph.d Dissertation “A Multidecadal Climate Signal Propagating Across the Northern Hemisphere”

where her third paper (chapter in her dissertation) found that

A network of simulated climate indices, reconstructed from a data set generated by models of the third Coupled Intercomparison Project (CMIP3 (Meehl et al. 2007)), is analyzed. None of the sixty analyses performed on these networks succeeded in reproducing a propagating signal. While model results varied from one another in the climate footprints simulated, their results were far more similar to one another than they were to observations found in the instrumental and proxy networks, implying physical mechanisms relevant to signal propagation may be missing from this suite of general circulation models.

Such failure at modeling circulation features certainly would influence regional ocean heating patterns.

Among the climate model failings are those reported in my post

Kevin Trenberth Was Correct – “We Do Not Have Reliable Or Regional Predictions Of Climate”

These include

Fyfe, J. C., W. J. Merryfield, V. Kharin, G. J. Boer, W.-S. Lee, and K. von Salzen (2011), Skillful predictions of decadal trends in global mean surface temperature,  Geophys. Res. Lett.,38, L22801, doi:10.1029/2011GL049508

who concluded that

”….for longer term decadal hindcasts a linear trend correction may be required if the model does not reproduce long-term trends. For this reason, we correct for systematic long-term trend biases.”

and

Stephens, G. L., T. L’Ecuyer, R. Forbes, A. Gettlemen, J.‐C. Golaz, A. Bodas‐Salcedo, K. Suzuki, P. Gabriel, and J. Haynes (2010), Dreary state of precipitation in global models, J. Geophys. Res., 115, D24211, doi:10.1029/2010JD014532.

who wrote

“models produce precipitation approximately twice as often as that observed and make rainfall far too lightly…..The differences in the character of model precipitation are systemic and have a number of important implications for modeling the coupled Earth system …….little skill in precipitation [is] calculated at individual grid points, and thus applications involving downscaling of grid point precipitation to yet even finer‐scale resolution has little foundation and relevance to the real Earth system.”

See also

Sun, De-Zheng, Yongqiang Yu, Tao Zhang, 2009: Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations. J. Climate, 22, 1287–1304.

who wrote

“…….extended calculation using coupled runs confirms the earlier inference from the AMIP runs that underestimating the negative feedback from cloud albedo and overestimating the positive feedback from the greenhouse effect of water vapor over the tropical Pacific during ENSO is a prevalent problem of climate models.”

De-Zheng also wrote in an EOS article

Climate Dynamics: Why Does Climate Vary?

“….even without any external forcing from human activity, the state of the climate system varies substantially.

“….one thing this book emphasizes is that, at least for interannual and decadal time scales, the climate is capable of varying in a substantial way in the complete absence of any external forces.”

Thus, the real world natural variations in upper ocean heat content may not be captured by the set of models used by Glecker et al 2012, despite their claim to the contrary.  To their credit, they do examine observed ocean trends in their analysis, but as they also state there remain limitations in the data, which is particularly true prior to the full deployment of the Argo network.

4. The Glecker et al 2012 paper also persists in using trends rather than time slices to assess change. A snapshot of the upper ocean heat content today compared to a snapshot for another year, as long as the data is spatially and temporally dense enough, provides a quantitative measure of the ocean warming over that time period. This change in heat can then be used to diagnose the global average radiative imbalance as Levitus et al 2012 did, and as I proposed in the paper

Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer.  Meteor. Soc., 84, 331-335.

While the regionally mapped ocean heat data from 0 to 700m is not available in a ready format on-line to compare with the models, the sea surface temperature anomalies are. Below is SST anomalies for the week of June 11.

Glecker et al 2012 present upper ocean heat changes for different ocean basins: North Atlantic, South Atlantic, North Pacific, South Pacific, North Indian and South India. Since we can use time slices, if we had a figure such as above for the 0-700m layer [and I encourage its creation by one of our readers], we could then directly compare the current state of the ocean heat content with the model predictions.

To the extent that the SST anomalies agree with the upper ocean heat anomalies ( a very important caveat, since the SSTs do have time lags since this is not a mass weighted temperature), what we see (using an eyecrometer) is in terms of the average is a warm North Atlantic, a  cool South Atlantic,  a highly variable North Pacific,  a less variable South Pacific but still a mixed signal,  a similar mixed signal for the North and South Indian Ocean. The global average SST anomaly is +0.192 deg as reported on the excellent weblog post by Bob Tisdale

May 2012 Sea Surface Temperature (SST) Anomaly Update

The Glecker et al paper has about a warming of the upper ocean of about a tenth of a degree so the SST anomaly is close to that value. However, the regional heat content anomlies (to the extent we can compare SSTs with upper ocean temperatures) are not in as good an agreement. Moreover, as recently as 1995, the global average SST anomalies were around zero and lower than +0.1C in 2008 (see from Bob’s analysis).

My bottom line conclusion is that, while Glecker et al 2012 is an informative paper and makes a comparison with real world data, they understate the role of non-greenhouse gases and natural climate variations as an explanation at least part of the recent warming. This disagreement will only be resolved, unfortunately, as time passes and we see further the evolution of the heat changes in the upper ocean.

Also, the authors should quantitatively compare observed regional time slices of heating for the different ocean basins and compare with the models for 2012. They should also make a prediction as to what we should see in the coming years, so that validation can be an ongoing process.

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