Comment To Andy Revkin On The Dot Earth Post “A-Sharp-Ocean-Chill-And-20th-Century-Climate”

Dot Earth has a post titled A Sharp Ocean Chill and 20th Century Climate

David W. J. Thompson, John M.Wallace, John J. Kennedy & Phil D. Jones, 2010: An abrupt drop in Northern Hemisphere sea surface temperature around 1970. Nature. doi:10.1038/nature09394

The abstract reads

“The twentieth-century trend in global-mean surface temperature was not monotonic: temperatures rose from the start of the century to the 1940s, fell slightly during the middle part of the century, and rose rapidly from the mid-1970s onwards. The warming– cooling–warming pattern of twentieth-century temperatures is typically interpreted as the superposition of long-term warming due to increasing greenhouse gases and either cooling due to a mid-twentieth century increase of sulphate aerosols in the troposphere, or changes in the climate of the world’s oceans that evolve over decades (oscillatory multidecadal variability). Loadings of sulphate aerosol in the troposphere are thought to have had a particularly important role in the differences in temperature trends between the Northern and Southern hemispheres during the decades following the Second World War2–4. Here we show that the hemispheric differences in temperature trends in the middle of the twentieth century stem largely from a rapid drop in Northern Hemisphere sea surface temperatures of about 0.3 C between about 1968 and 1972. The timescale of the drop is shorter than that associated with either tropospheric aerosol loadings or previous characterizations of oscillatory multidecadal variability. The drop is evident in all available historical sea surface temperature data sets, is not traceable to changes in the attendant metadata, and is not linked to any known biases in surface temperature measurements. The drop is not concentrated in any discrete region of the Northern Hemisphere oceans, but its amplitude is largest over the northern North Atlantic.”

In response to Andy’s alerting me to this post, I replied 

Hi Andy

 This is a very good Dot Earth post. The Thompson et al paper is an example of what we discussed in our paper

Rial, J., R.A. Pielke Sr., M. Beniston, M. Claussen, J. Canadell, P. Cox, H. Held, N. de Noblet-Ducoudre, R. Prinn, J. Reynolds, and J.D. Salas, 2004: Nonlinearities, feedbacks and critical thresholds within the Earth’s climate system. Climatic Change, 65, 11-38.
https://pielkeclimatesci.files.wordpress.com/2009/10/r-260.pdf.

As we wrote in the abstract

“The Earth’s climate system is highly nonlinear: inputs and outputs are not proportional, change is often episodic and abrupt, rather than slow and gradual, and multiple equilibria are the norm. While this is widely accepted, there is a relatively poor understanding of the different types of nonlinearities, how they manifest under various conditions, and whether they reflect a climate system driven by astronomical forcings, by internal feedbacks, or by a combination of both.”

We present examples of this nonlinear behavior across a variety of space and time scales in our paper.

Among our conclusions is that we recommend to

“[i]mprove our vision of the climate’s future through a better understanding of its history. Paleoclimate and hydroclimate records exhibit abrupt changes in the form of rapid warming events, the irregular oscillations of ENSO, catastrophic floods, sustained droughts, and many other nonlinear response characteristics. Extracting, identifying, categorizing, modeling and understanding these nonlinearities will greatly help our ability to understand the present and future state of the climate”

and

“Understand the global connectivity and variability of ocean-atmosphere coupled phenomena, such as the North Pacific Oscillation (NPO), the Pacific Decadal Oscillation (PDO), the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), and the El Niño/Southern Oscillation (ENSO).”

In the comments on Dot Earth, I note that there remains an impression that models can be used to explain the observations. However, models are only hypotheses which must be tested in terms of their skill at prediction. It is clear that the multi-decadal global models remain unable to skillfully simulate regional ocean/atmospheric features such as exemplified in the Thompson et al paper.

I also agree with the comments of Carl Wunsch that there is a limited selection of papers that are highlighted. We need a way to be more inclusive and your weblog is serving as an excellent venue for this purpose.

Best Regards

Roger Sr.

P.S. My comment above can be posted if you chose to.

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