[ UPDATE : REUTERS GETS THE KEY POINT THAT RICHARD BLACK APPEARS TO HAVE MISSED : http://www.reuters.com/article/idUS253216740320100923 : “Global Warming May Have Slowed in the 1970s Due to Suddenly Cooler Oceans…the article also suggests that the cooling coincided with an unexpected influx of freshwater, most likely from melting ice, that flowed from the Arctic Ocean into the North Atlantic.” ]
Global Warming May Have Slowed in the 1970s Due to Suddenly Cooler Oceans”Richard Black seems to have been told to raise the level of uncertainty over Climate Change Science :-
“23 September 2010 : Oceans divide over 1970s warming : By Richard Black : Environment correspondent, BBC News : The surfaces of the oceans went through a short period of rapid temperature change 40 years ago, scientists have found – but the cause is unknown. Top layers of Northern Hemisphere water cooled by about 0.3C; the south saw roughly the same degree of warming. Writing in the journal Nature, the team suggests that air pollution cannot be responsible for the changes, as has been suggested for mid-century cooling. They do not suggest a cause. It is not clear what could link all the oceans…”
Hang on a minute !
What does the Nature Letter actually say ?
I asked for a PDF from David W. J. Thompson, which he kindly provided :-
“…The resulting regression map reveals that the drop is reflected throughout much of the world’s ocean, but has its largest amplitude over the northern North Atlantic. The spatial concentration of the drop can also be seen in residual SST [sea surface temperatures] time series calculated for select Northern Hemisphere ocean areas; it is evident in area averages for the entire North Atlantic and North Pacific Oceans, but has its largest amplitude in data averaged over the northern North Atlantic, above 50 degrees N [North]. This region is marked by large exchanges of heat between the ocean and atmosphere that are considered capable of influencing hemispheric-mean temperature. The timing of the drop corresponds closely to a rapid freshening of the northern North Atlantic in the late 1960s/early 1970s (the ‘great salinity anomaly’)…”
“…The suddenness of the drop in Northern Hemisphere SSTs is reminiscent of ‘abrupt climate change’, such as has been inferred from the palaeoclimate record, but is inevitably obscured in analyses of twentieth century decadal variability based on low-pass filtered versions of the SST data…”
“…The timescale of the drop is important, because it is considerably shorter than that typically associated with either tropospheric aerosol forcing or oscillatory multidecadal SST variability. The horizontal structure of the drop is also of interest, because it indicates that the drop might reflect atmosphere–ocean interaction in the dynamically active northern North Atlantic…”
So, contrary to what Richard Black summarises, the authors are effectively suggesting a cause.
[ Citation : “An abrupt drop in Northern Hemisphere sea surface temperature around 1970”, Thompson D. W. J. et al. Letter in Nature. : doi:10.1038/nature09394 : Vol. 467, 23 September 2010 pp 444 – 447 ]