NOTE: As is typical these days, and in keeping with co-author Phil Jones tradition of not giving up anything, the publicly funded scientific paper is not included with the news, and is hidden behind a paywall. All we can get is the press release and abstract and this silly picture of the researcher grinning like a banshee. Speculate away with impunity. I wonder why he has the ozone hole in Antarctica next to the HadCRUT temperature series?

Caption: David W.J. Thompson, professor of atmospheric science at Colorado State University, is the lead author of a Nature paper that shows sudden ocean cooling contributed to a global warming hiatus in the middle 20th century in the Northern Hemisphere. Credit: Colorado State University

FORT COLLINS – The hiatus of global warming in the Northern Hemisphere during the mid-20th century may have been due to an abrupt cooling event centered over the North Atlantic around 1970, rather than the cooling effects of tropospheric pollution, according to a new paper appearing today in Nature.

David W. J. Thompson, an atmospheric science professor at Colorado State University, is the lead author on the paper. Other authors are John M. Wallace at the University of Washington, and John J. Kennedy at the Met Office and Phil D. Jones of the University of East Anglia, both in the United Kingdom.

The international team of scientists discovered an unexpectedly abrupt cooling event that occurred between roughly 1968 and 1972 in Northern Hemisphere ocean temperatures. The research indicates that the cooling played a key role in the different rates of warming seen in the Northern and Southern Hemispheres in the middle 20th century.

“We knew that the Northern Hemisphere oceans cooled during the mid-20th century, but the sudden nature of that cooling surprised us,” Thompson said.

While the temperature drop was evident in data from all Northern Hemisphere oceans, it was most pronounced in the northern North Atlantic, a region of the world ocean thought to be climatically dynamic.

“Accounting for the effects of some forms of natural variability – such as El Nino and volcanic eruptions – helped us to identify the suddenness of the event,” Jones said.

The different rates of warming in the Northern and Southern Hemispheres in the middle 20th century are frequently attributed to the larger buildup of tropospheric aerosol pollution in the rapidly industrializing Northern Hemisphere. Aerosol pollution contributes to cooling of the Earth’s surface and thus can attenuate the warming due to increasing greenhouse gases.

But the new paper offers an alternative interpretation of the difference in mid-century temperature trends.

“The suddenness of the drop in Northern Hemisphere ocean temperatures relative to the Southern Hemisphere is difficult to reconcile with the relatively slow buildup of tropospheric aerosols,” Thompson said.

“We don’t know why the Northern Hemisphere ocean areas cooled so rapidly around 1970. But the cooling appears to be largest in a climatically important region of the ocean,” Wallace said.

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Global temperatures 1850-2010 [Nature News]

An abrupt drop in Northern Hemisphere sea surface temperature around 1970 David W. J. Thompson1, John M. Wallace2, John J. Kennedy3 & Phil D. Jones4 Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado 80523, USA Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195-1640, USA Met Office Hadley Centre, Met Office, Exeter EX1 3PB, UK Climatic Research Unit, University of East Anglia, Norwich NR4 7TJ, UK Correspondence to: David W. J. Thompson1 Email: davet@atmos.colostate.edu Top of page Abstract 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 onwards1. 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 troposphere2, 3, 4, or changes in the climate of the world’s oceans that evolve over decades (oscillatory multidecadal variability)2, 5. 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, 3, 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. ============================= hmmm, maybe this graph from ICECAP will help them: And this too: The historical variability of the Arctic Oscillation. 1969-1970 was darned cold. Also see this image from the Climate Prediction Center: ALSO: Quote from Phil Jones: Reuters Jones, at the centre of a furore over e-mails hacked from the University of East Anglia in late 2009, was reinstated this year after reviews cleared him of suspicions of exaggerating evidence in favour of global warming. Thursday’s paper is the first he has since published in Nature. “Maybe it will get them thinking,” he said, asked how climate sceptics would react to his involvement in a paper highlighting a cause of cooling, rather than warming. ——————- I wonder how good that Southern Hemisphere SST data is back in the 1960s, which is used here to demonstrate “robustness”. From Physicsworld.com

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