My Perspective On The Nature Commentary By Kevin Trenberth

As readers of my weblog know, there are a set of posts giving e-mails among Kevin Trenberth, Josh Willis and I, and blog posts by Roy Spencer, on the issue of “missing heat” in the climate system. These posts can be viewed at

There is now a new contribution by Kevin on Nature (it is actually not new in one sense, since Kevin (and J. Fasullo) recently posted a commentary on the same subject at Science magazine. Nature soliciting the same person (no matter how qualified) to write a comment is not expanding our perspective on this issue (Roy Spencer, for example, would have been a good choice as he has a different viewpoint than Kevin expressed in his Science comment).

The Nature comment is

Kevin E. Trenberth, 2010: The ocean is warming, isn’t it? Nature 465, 304-304 (19 May 2010) doi:10.1038/465304a News and Views

The abstract reads

“A reappraisal of the messy data on upper-ocean heat content for 1993–2008 provides clear evidence for warming. But differences among various analyses and inconsistencies with other indicators merit attention.”

The Trenberth commentary is in response to the paper (which I posted on this past Friday; see)

John M. Lyman, Simon A. Good, Viktor V. Gouretski, Masayoshi Ishii, Gregory C. Johnson, Matthew D. Palmer, Doug M. Smith, Josh K. Willis, 2010: Robust warming of the global upper ocean. Nature 465, 334-337 (20 May 2010) doi:10.1038/nature09043 Letter

The abstract of the Lyman et al paper reads

A large (~1023 J) multi-decadal globally averaged warming signal in the upper 300 m of the world’s oceans was reported roughly a decade ago and is attributed to warming associated with anthropogenic greenhouse gases. The majority of the Earth’s total energy uptake during recent decades has occurred in the upper ocean, but the underlying uncertainties in ocean warming are unclear, limiting our ability to assess closure of sea-level budgets, the global radiation imbalance and climate models. For example, several teams have recently produced different multi-year estimates of the annually averaged global integral of upper-ocean heat content anomalies (hereafter OHCA curves) or, equivalently, the thermosteric sea-level rise. Patterns of interannual variability, in particular, differ among methods. Here we examine several sources of uncertainty that contribute to differences among OHCA curves from 1993 to 2008, focusing on the difficulties of correcting biases in expendable bathythermograph (XBT) data. XBT data constitute the majority of the in situ measurements of upper-ocean heat content from 1967 to 2002, and we find that the uncertainty due to choice of XBT bias correction dominates among-method variability in OHCA curves during our 1993–2008 study period. Accounting for multiple sources of uncertainty, a composite of several OHCA curves using different XBT bias corrections still yields a statistically significant linear warming trend for 1993–2008 of 0.64 W m-2 (calculated for the Earth’s entire surface area), with a 90-per-cent confidence interval of 0.53–0.75 W m-2.

Unfortunately, Kevin (nor the Lyman et al paper which includes Josh Willis as one of the co-authors) includes any of the discussion in the e-mails that I posted where there is no evidence of significant heat being accumulated in recent years at depths lower than 700m. However, Kevin does acknowledge a “slowdown since 2003” of heating.

Kevin’s statement

“Moreover, methods of analysis and interpolation of gaps in space and time should take account of the warming climate, and care is needed not to bias results towards background values”

however, is puzzling as it implies that heat has to be added to the analysis even if it is not directly measured! The background (i.e. measured values) are what should be used.

While it is unfortunate that he did not use the Nature commentary to include the perspective that Josh Willis provided to him in the e-mail exchanges and Roy Spencer provided in his blog posts, Kevin does agree with us that

“More robust indicators of a warming planet come from evidence of increasing ocean heat content and associated sea-level rise.”

and

“As the relevant analytical methods mature, ocean heat content is likely to become a key indicator of climate change.”

Both of these conclusions are what I proposed in my paper

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

where the abstract reads

“The assessment of heat storage and its changes over time should be a focus of international climate monitoring programs.”

with the conclusion reading

In conclusion, there are several major reasons that the assessment of the earth system’s heat budget is so valuable.

• The earth’s heat budget observations, within the limits of their representativeness and accuracy, provide an observational constraint on the radiative forcing imposed in retrospective climate modeling.

• A snapshot at any time documents the accumulated heat content and its change since the last assessment. Unlike temperature, at some specific level of the ocean, land, or the atmosphere, in which there is a time lag in its response to radiative forcing, there are no time lags associated with heat changes.

• Since the surface temperature is a two-dimensional global field, while heat content involves volume integrals, as shown by Eq. (1), the utilization of surface temperature as a monitor of the earth system climate change is not particularly useful in evaluating the heat storage changes to the earth system. The heat storage changes, rather than surface temperatures, should be used to determine what fraction of the radiative fluxes at the top of the atmosphere are in radiative equilibrium. Of course, since surface temperature has such an important impact on human activities, its accurate monitoring should remain a focus of climate research (Pielke et al. 2002a).”

There is also an interesting statement in the Lyman et al 2010 paper

“…sea surface temperatures have been roughly constant since 2000…”

which I will discuss further in an upcoming post since this means any global average surface temperature increase since 2000 must have occurred on land (yet, as we have seen (e.g. see), there is a warm bias in the land surface temperature trend assessments presented by NCDC, GISS and CRU).

My Perspective On The Nature Commentary By Kevin Trenberth

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