At their “Die kalte Sonne” site, geologist Dr. Sebastian Lüning and chemist Prof. Fritz Vahrenholt write that Stefan Rahmstorf of the alarmist Potsdam Institute for Climate Impact research has had to watch another one of his alarmist claims go down in flames.
In March 2015 Stefan Rahmstorf (“stefan”) spread a hyped up alarm story at the IPCC-friendly climate blog Real Climate.
A cold anomaly in the Atlantic, off the east coast of Greenland, was alleged to be the proof that the Gulf Stream was gradually weakening – a consequence of man-made climate warming!
“stefan” wrote at Realclimate:
What’s going on in the North Atlantic?
The North Atlantic between Newfoundland and Ireland is practically the only region of the world that has defied global warming and even cooled. Last winter there even was the coldest on record – while globally it was the hottest on record. Our recent study (Rahmstorf et al. 2015) attributes this to a weakening of the Gulf Stream System, which is apparently unique in the last thousand years. […] It happens to be just that area for which climate models predict a cooling when the Gulf Stream System weakens (experts speak of the Atlantic meridional overturning circulation or AMOC, as part of the global thermohaline circulation). That this might happen as a result of global warming is discussed in the scientific community since the 1980s – since Wally Broecker’s classical Nature article “Unpleasant surprises in the greenhouse?” Meanwhile evidence is mounting that the long-feared circulation decline is already well underway.
Rahmstorf showed the following chart (“Linear temperature trend from 1900 to 2013″):
In his post the Postdam PIK scientist painted a climate horror scenario, suggesting that it was something far worse than anything ever previously anticipated.
Subsequently international colleagues took it upon themselves to validate the Rahmstorfian horror scenario. One year later we now have the results of the examination.
On June 29, 2016, Femke de Jong and Laura de Steur of the Dutch NIOZ Institute at the OSNAP project site announced the results in a press release: Rahmstorf and his model were totally off. The especially observed North Atlantic cold anomaly in the winter 2014/15 had nothing to do with a weakening Gulf Stream, rather it was much more the consequence of a powerful vertical mixing with cold low level water.
The press release states:
A new record in mixing of surface and deep ocean water in the Irminger Sea has important consequences for the Atlantic overturning circulation
Scientists Femke de Jong and Laura de Steur of the NIOZ Royal Netherlands Institute for Sea Research have shown that the recent temperature changes in the Irminger Sea between Iceland and Greenland can be explained through regional ocean-atmosphere interaction during the cold winter of 2014-2015. This rejects a hypothesis that posed that increased meltwater from Greenland weakened deep water formation and caused the cold blob. The article by de Jong and de Steur is accepted by Geophysical Research letters and has appeared online.
Deep water formation is an important process in the global ocean circulation. When high latitude winters are cold enough, the salty surface water of the North Atlantic cools enough to increase its density and mix with underlying deeper waters. This mixing is called deep convection. It forms the vertical link between the warm northward flow near the surface and the cold southward flow along the bottom, which is generally referred to as the Atlantic Meridional Overturning Circulation. The transport of warm water in the overturning circulation is partly responsible for the mild climate in northwestern Europe compared to similar latitudes in North America.
In climate model simulations the strength of convection south of Greenland is related to the strength of the overturning circulation. Some models predict that convection will weaken due to the input of freshwater released from the melting ice on Greenland. Because of the much lower density of freshwater compared to seawater it forms a barrier that isolates the deep ocean from the cold atmosphere. While the majority of the Earth warms as a result of climate change the region around southern Greenland would cool.
In temperature observations of the earth’s surface in 2015 a similar pattern seems to appear. The Earth warmed while the ocean southeast of Greenland cooled. This led to speculation that convection had already weakened as a result of increased melting of Greenland’s icecap. It would mean that the overturning circulation would be affected faster than expected.
Instruments moored in the Irminger Sea, southeast of Greenland, shows that this is not (yet) the case. This mooring, deployed by the Royal Netherlands Institute for Sea Research (NIOZ) at 3 km depth in 2003, shows that convection strengthened in recent years. Record depths of convection were observed in the Irminger Sea in the winter of 2014-2015. This strong mixing was caused by an extremely cold and long winter. Two NIOZ scientists, Femke de Jong and Laura de Steur, have shown that the temperature evolution in the Irminger Sea (including the strong decrease in 2015) can be explained through regional interaction between the ocean and atmosphere. The manuscript that describes the convection and explains the temperature changes is accepted in Geophysical Research Letters. This coincides with a publication by a German group in Nature Geoscience this week, in which they use a model to show that it will take some time before freshwater from Greenland enters the deep water formation regions in large enough amount to weaken convection.
The measurements in the Irminger Sea were partly funded by the European North Atlantic CLIMate (NACLIM) project and are part of the international OSNAP (Overturning in the Subpolar North Atlantic Program). The goal of OSNAP is to quantify the overturning circulation and its heat transport at high latitudes and to establish a relation to convection and wind forcing. On the 26th of July a research expedition will return to the Irminger Sea to recover the NIOZ and other OSNAP moorings and do a hydrographic survey. This cruise can be followed on the OSNAP blog at www.o-snap.org. A short video documentary of last year’s cruise can be found on youtube (https://www.youtube.com/watch?v=a-lhCIQjE4c).
In the paper’s abstract in the Geophysical Research Letters, Femke de Jong and Laura de Steur leave little doubt that the Gulf Stream continues to flow reliably:
Strong winter cooling over the Irminger Sea in winter 2014–2015, exceptional deep convection, and the emergence of anomalously low SST
Deep convection is presumed to be vital for the North Atlantic Meridional Overturning Circulation, even though observational evidence for the link remains inconclusive. Modeling studies have suggested that convection will weaken as a result of enhanced freshwater input. The emergence of anomalously low sea surface temperature in the subpolar North Atlantic has led to speculation that this process is already at work. Here we show that strong atmospheric forcing in the winter of 2014–2015, associated with a high North Atlantic Oscillation (NAO) index, produced record mixed layer depths in the Irminger Sea. Local mixing removed the stratification of the upper 1400 m and ventilated the basin to middepths resembling a state similar to the mid-1990s when a positive NAO also prevailed. We show that the strong local atmospheric forcing is predominantly responsible for the negative sea surface temperature anomalies observed in the subpolar North Atlantic in 2015 and that there is no evidence of permanently weakened deep convection.”
This is yet another failure for Stefan Rahmstorf and his Potsdam climate alarmism factory.
It is refreshing to see that the international research community is increasingly resisting these dubious PIK creations. It is also time for the German press to report on these results for the sake of balance. The Washington Post showed how to do it on 30 June 2016:
The mysterious ‘cold blob’ in the North Atlantic Ocean is starting to give up its secrets
[…] Stefan Rahmstorf, an ocean physicist with the Potsdam Institute for Climate Impact Research and author of the study mentioned above, has writtenthat very cold temperatures in the subpolar North Atlantic Ocean in the winter of 2014-2015 “suggests the decline of the circulation has progressed even further now than we documented in the paper.” But in a new study in Geophysical Research Letters reporting on deep ocean measurements from this region, two researchers present an alternative interpretation. They say that they found “exceptional” levels of deep ocean convection, or mixing of surface waters with deep waters of a sort that helps drive the overturning circulation, during in the winter of 2014-2015 — the height of the cold “blob.” And they attribute that temperature phenomenon to natural climate variability, driven by local weather and winds. “We find that the observed temperature variability is explained without invoking a trend in the lateral heat transport that would be representative of an AMOC slowdown,” Femke de Jong and Laura de Steur of the Royal Netherlands Institute for Sea Research write in the paper. […]”
Read the entire article at the Washington Post.