by Judith Curry
The hiatus lives.
The recent paper by Karl et al., discussed at Has NOAA busted the pause in global warming?, presented a new surface temperature data set that does NOT support the notion of a ‘slowdown’ in global surface temperature increase. Karl et al. found a global trend 2000-2014 to be 0.116C/decade, with an ocean trend of 0.99C/decade. The paper received a HUGE amount of publicity.
A new paper published by Science is just what I have been waiting for, an integrative look at global ocean data in recent decades:
Recent hiatus caused by decadal shift in Indo-Pacific heating
Veronical Nieves, Josh Willis, William Patzert
Abstract. Recent modeling studies have proposed different scenarios to explain the slowdown in surface temperature in the most recent decade. Some of these studies seem to support the idea of internal variability and/or rearrangement of heat between the surface and the ocean interior. Others suggest that radiative forcing might also play a role. Our examination of observational data over the past two decades shows some significant differences compared to model results from reanalyses, and provides the most definitive explanation of how the heat was redistributed. We find that cooling in the top 100-meter layer of the Pacific Ocean was mainly compensated by warming in the 100- to 300-meter layer of the Indian and Pacific Oceans in the past decade since 2003.
The paper is published in Science [link].
The global average surface temperature has been rising since 2003 by +0.001°C/year. Although not zero, it is slower than the century time-scale warming of +0.0064 ± 0.0015°C/year since 1880 (2). The surface warming of the 00s is also substantially slower than the 90s, which warmed at a rate of +0.008°C/year.
JC comment: Referring to the Supplementary Information, I see that they used the NOAA OI SST data set, available since 1985. The methodology includes bias adjustment of satellite and ship observations (referenced to buoys) to compensate for platform differences and sensor biases (hooray – they adjust other biased data sets to the more robust buoys). While the trend of 0.01C/decade since 2003 is over a different period, this trend value is starkly different from Karl et al. trend from 2000-2014 of 0.099C/decade. I don’t know why I didn’t think of the OI SST dataset when discussing the Karl dataset, I used to use this dataset a lot. Is OI SST perfect? No, but I think the methodology makes a lot more sense for recent decades than the Karl et al methodology.
Our analysis indicates that during the most recent decade, cooling in the top 100 m layer of the Pacific Ocean is compensated by warming in the 100 to 300 m layer of the Western Pacific and Indian Oceans with the largest contribution in the tropics. The Southern Ocean plays a secondary role in warming the 100-300 m layer, but this warming is steady over both of the past decades. The Atlantic Ocean does show a switch from warming to cooling, but its area is so small that it cannot meaningfully con-tribute to the hiatus signal in surface temperature over the past decade.
Analysis of deep hydrographic data in comparison with satellite measurements of sea level change indicates a contribution of 0.76 mm/year of sea level rise due to thermal expansion within 700-2000 m. Assuming a thermal expansion coefficient of 1.3 × 10−4 °C−1 for that layer, this implies an average warming of 0.0045°C/year between the mid-90s and mid-00s and between 700 and 2000 m. The WOA pentadal estimate shows a heat content increase of 2.4 × 1021 J/year or about 0.0015°C/year (1993-2002 period, 700-2000 m layer). The latter is consistent with the 0.0013°C/year rate of warming for the 700-1500 m layer as measured by the Argo array in the 00s . Together, these findings suggest no significant increase in the rate of warming below 700 m since 2003.
JC comment: In plain words, there doesn’t seem to be any observational evidence that Trenberth’s ‘missing heat’ is hiding below 700 m.
Interestingly, reanalysis also do not seem to correctly reproduce the ocean warming rates and lie well outside the observation uncertainty at different depths and times. Both the hiatus and the net amount of heat absorbed by the ocean below 700 m are overestimated. Reanalyses are also inconsistent with ocean observations, in terms of the vertical and regional distribution of heating.
JC comment: Trenberth claimed to have found the ‘missing heat’ in the deep ocean from the ECMWF reanalyses [link]. Looks like this was an artifact of the analysis process.
The observational rate of heat content increase over the 0-1500 m depth range did not change significantly between the 90s (2.0 × 1021 J/year) and the 00s (3.4 × 1021 J/year or 2.53 × 1021 J/year according to the observational average or Argo, respectively). Thus, observational heat content estimates do not reveal any obvious hiatus. This suggests that since the early 90s there has been a steady rate of net ocean heat uptake, and the amount of radiative imbalance at the top of the atmosphere remained practically unchanged between the 90s and the 00s. This contradicts one recent study suggesting that the net ocean heat uptake was reduced during the 00s on the basis of changes in surface flux estimates.
JC comment: The last sentence in the paper is the only statement in the paper that I disagree with. Their analysis is not sufficient to close the global energy budget or to rule out a change in external forcing or cloudiness in contributing to the hiatus.
This paper is important in clarifying the vertical and horizontal distribution of subsurface temperature changes in the ocean. And I am particularly glad to be reminded of the OI SST data set, which may be the best SST data set to use for recent decades. The hiatus clearly lives, both in upper ocean heat content and surface temperatures from OI SST data set. The Karl et al. ocean data seems inconsistent with the upper ocean heat content measurements (not to mention the OI SST data set). I am also relieved to see a careful comparison of the ocean reanalyses (e.g. NCEP, ECMWF) with observations, highlighting the deficiencies of the NCEP and ECMWF ocean reanalyses relative to observations. Rather extravagant and overconfident claims have been made about the ocean reanalyses, which are unjustified based on the actual observations.
This paper lays out a challenge not only for ocean reanalysis, but for also improving model treatment of vertical heat transfer in the ocean.
Well, it will certainly be interesting to see what the media does with this paper, after declaring the hiatus an artifact several weeks ago. This new paper, published in the same journal as the Karl paper (Science), should have come to the attention of the same journalists as the Karl paper (although I did not see any press release associated with this paper). I received an advanced copy of the paper from someone in a skeptics organization – no queries from journalists or anything. It will be interesting to see how (or if) this paper plays out in the mainstream media.