The paper by Grevemeyer, Herber and Essen (2000) is a worry; and one wonders how it survived peer-review.  This exercise in wishful-thinking begins:

 Observations of the Earth’s near-surface temperature show a global increase  since 1901, occurring from 1925-44 and 1978-1997.  Over these periods global  temperature rose by 0.37 and 0.32 K, respectively.  The temperature change over  the past decade is unlikely to be entirely due to internal climate variability and  has been attributed to changes in the concentration of greenhouse gases caused  by human activity.

I smell a mind-set here.  These authors relate microseisms recorded at the Hamburg seismological station to winter wave climate in the NE Atlantic; and they derive an index for the amplitude of secondary microseisms with periods of 6-8 seconds, plotted in the top graph of Figure 1, as a proxy for changes in the wave climate.  Implausibly, they provide near the end of the paper an explanation for their observations as follows:

 Recent simulations and analyses of the Earth’s temperature pattern exclude  purely natural forcing and attribute it largely to changes in the concentration of  greenhouse gases and aerosol loading due to human activity.  Therefore, it seems  reasonable to propose that greenhouse forcing affects the ocean’s wave climate  and hence coastal surf and storm surges along northern Europe’s coastlines,  which in turn produced the observed increase in microseisms.
As the only crumbs of evidentiary support of their conclusion, they include a short run of wave height measurements off Land’s End in the middle graph of Figure 1, and a longer run of near-surface temperatures for the Northern Hemisphere in the lower graph.

The source of their problem is obvious.  These authors can’t tell the difference between a step-change and a trend.  They have been mesmerised by the purported “linear trends” which they superimposed on the data in the three graphs of Figure 1.

Quite rightly, they drew a horizontal line representing the 1954-77 years, ie the years leading up to the prominent step in their wave-climate proxy record.  If they had left out their spurious superimposed trend, and drawn instead a second horizontal line through the years following the step in their record, all would have been well.

I have here reproduced their plot, after removing the line illustrating the “linear trend”, in Figure 2 (a).  The step in the record is unmistakable.  Doubtless, Grevemeyer et al would now recognise the similarly-timed step in temperature of the lower atmosphere, as measured by balloon-borne thermometers, shown in Figure 2 (b).

Once they had seen the obvious correlation in Figure 2, they would have twigged.  The step-change in global temperature of the lower atmosphere at 1976/77- with little trend, before or after, in the whole 43-year record - is an outcome of the most notable natural climatic event of the 20th century.  It has little or nothing to do with greenhouse.

This step-change in atmospheric temperature at 1976/77 stems from a sudden nonlinear transition between climatic regimes.  At this time:
* Globally-averaged temperatures in the lower atmosphere jumped 0.3 0C.
* Sea-surface temperature in the central equatorial Pacific jumped 0.6 0C.
* SST in the southern California Current during upwelling season increased 11/2 to 3 0C.  * Concurrently, the PDO index, an indicator of variation in the supply of cold, deep, water to the NE Pacific, made a step-change in the direction of reduced upwelling.
* The heat-content of the top 300 metres of the world’s oceans increased.
* This jump was most clear-cut in the Atlantic, where wave activity (in the NE Atlantic, as described herein) also strengthened.
* The ENSO index, relating to the eastern equatorial Pacific, made a pronounced step in the direction of its warmer (ie more-frequent El Niño) phase.
* Upwelling-season SST in the eastern equatorial Pacific made a step-like warming, which has not yet been reversed.
* SST in the subtropical South Pacific at Raratonga (21 0S) peaked in 1976, and cooled about 2 0C over the following decade.

The 1976/77 event relates to a major re-ordering of oceanic heat transportation, and coincides with a change in the rate-of-change of the length of day.  LOD variations imply the involvement of inertial factors, and inertial changes impede the continuity of oceanic circulation - particularly in the geometrically-complex North Atlantic Basin.

In Figure 3(a), I reproduce the lowermost graph in Figure 1, extended to include the whole of the 20th century.  As you can see, there are two periods of pronounced surface warming.  Although the correlation is more compelling for that in the second half of the century, both periods of warming are related to a reduction in the upwelling of cold, deep water in the eastern Pacific, as shown in Figure 3(b).

In seeking the most likely explanation for the changing NE Atlantic winter wave-climate, the abundant evidence in favour of the (now well-documented) global-scale and ocean-related nonlinearity at 1976/77 failed to get a mention, let alone serious consideration, by Grevemeyer et al.

Instead, in a desperate attempt to sing the greenhouse song, they drew a sloping straight line between the beginning and end of their run of data - the broken line shown on the top graph of Figure 1, and removed by me in Figure 2(a) - and called it a ‘trend’.  Everything that didn’t suit their preconception about greenhouse was ignored.

Can this be what we mean when we speak of the ‘scientific method’?

Grevemeyer, I., R. Herber and H.-H. Essen 2000, “Microseismological evidence for a  changing wave climate in the northeast Atlantic Ocean”, Nature v 408 pp 349-52.
Michaels, Patrick J. and Robert C. Balling Jr 2000, The Satanic Gases: clearing the air  about global warming, Cato Institute Washington DC, 234 p.
Stott, Lowell D. et al 2000, “Increased dissolved oxygen in Pacific intermediate waters  due to lower rates of carbon oxidation in sediments”, Nature v 407 pp 367-70.

You read it first here

© 2001  Bob Foster
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